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Published: 17 March 2023

Assessing the relative impacts and economic costs of Japanese knotweed management methods

Sophie Hocking ORCID: orcid.org/0000-0002-7475-6156 1 ,
Trisha Toop ORCID: orcid.org/0000-0003-2910-1764 2 , 3 ,
Daniel Jones ORCID: orcid.org/0000-0002-3192-6450 1 , 4 ,
Ian Graham 5 &
Daniel Eastwood ORCID: orcid.org/0000-0002-7015-0739 1

Scientific Reports volume 13 , Article number: 3872 ( 2023 ) Cite this article

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Environmental impact

Sustainable land management encompasses a range of activity that balance land use requirements with wider conservation and ecosystem impact considerations. Perennial invasive alien plants (IAPs), such as Japanese knotweed, cause severe ecological and socio-economic impacts, and methods to control their spread also come at a cost. Synthetic herbicides are generally viewed as less sustainable and more ecologically damaging than alternative approaches. Here we used a comparative Life Cycle Assessment to evaluate the sustainability of herbicide-based management approaches and physical alternatives, using a large-scale Japanese knotweed field study as a model IAP system. Glyphosate-based methods elicited the lowest environmental impacts and economic costs during production. Geomembrane covering and integrated physiochemical methods were the costliest and imposed the greatest impacts. We discuss the costs and benefits of chemical and physical approaches for the sustainable management of invaded land and question how sustainable environmental stewardship is defined for the control of IAPs.

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Introduction.

As global focus on environmental sustainability rises, herbicides have been scrutinised due to their environmental, ecological and social impacts 1 , 2 . Herbicide application plays an important role in managing invasive alien plants (IAPs) 3 , which themselves impose negative impacts 4 , 5 , 6 . However, with increasing demand for sustainable solutions, alternative management methods are postulated to impose less damage 7 . The viability of biocontrol agents has been investigated 8 , 9 , the use of root exudates and other natural alternatives 2 and physical management methods such as mowing 10 , excavation 11 , covering (reviewed by Dusz et al. 12 ), and electrical treatment 13 are also gaining interest to ensure alignment with sustainable management goals.

Despite increasing focus on novel management solutions, evidence of the relative impacts of these different approaches is limited. Moreover, impact assessments often focus on implications following application; this represents just one stage in the life cycle of IAP management methods. Raw material extraction, production, formulation, packaging, storage, transport and use are intrinsic processes of any approach used for IAP control. If these stages are omitted from assessment, prioritisation of IAP treatment options may become skewed towards those that exhibit low impacts in the use and post-use phase, irrespective of their overall environmental risk. Regardless of motivation to constrain herbicide use, chemical methods are particularly important for some invasive plants 3 . Japanese knotweed ( Reynoutria japonica var. japonica ) is a well-known example of the difficulties associated with perennial IAP management. Complications in managing knotweed arise from its plasticity in environmental tolerance 14 , 15 , resilience to physical disturbance 16 , 17 , vegetative dispersal capabilities 18 , and extensive energy storage in rhizomes 19 . This IAP negatively impacts native ecosystems, reducing biodiversity and altering provision of ecosystem services 20 , 21 . The perceived threat of property damage resulting from knotweed infestation has also impacted mortgage lending and housing valuation 22 . Sustainable management is therefore imperative.

Numerous treatment methods have been proposed for Japanese knotweed 8 , 11 , 23 with varying degrees of success. Physical methods (including covering, cutting, burning, digging and encapsulation) are of particular interest as they are considered more efficient for development sites. However, these methods are labour intensive, expensive and some (particularly cutting) may exacerbate knotweed dispersal 24 . Biological control has also been researched extensively as an environmentally friendly option, albeit with limited evidence of success to-date 25 . Chemical approaches employing glyphosate are considered the most successful for knotweed management 23 , 24 . Nevertheless, there are negative social perceptions of herbicides due to concerns around impacts to biodiversity and human health. This increases the risk of deregulation, jeopardising effective knotweed management 26 and wider IAP control; particularly given that rates of biological invasion have not yet reached saturation 27 .

There is a trade-off between control efficacy and the impacts of management 28 ; both facets of our wider responsibility to mitigate negative anthropogenic effects on the environment. Understanding the consequences of this relies on long-term data collection at a relevant scale, a key gap in invasion science 29 . To avoid shifting burdens, management options must be informed by control efficacy and impacts to the environment and human health 28 , 30 . Impacts across the life cycles of treatment methods should be considered to determine the true sustainability of IAP management and identify priorities that align with national and global commitments to sustainability and natural resource management 31 .

Economic costs are also pertinent to the selection of IAP management strategies. The global annual cost of invasive species management is estimated to be US$26.8 billion 32 . Japanese knotweed has been calculated to cost £165,609,000 per year in the UK 4 . Current estimates of costs are primarily associated with knotweed management at development sites, road and rail networks, in private land or gardens, and in semi-natural habitats. Indirect costs associated with knotweed include legal advice and action, and property devaluation. Thus, the economic costs of knotweed impact a variety of sectors as well as the general public and local authorities. Comparing the cost of management methods can inform viability and prioritisation of methods to ensure effective resource use, particularly relevant when managing at scale.

Public perception is increasingly important for the reporting and implementation of sustainable invasive species management 33 . Value systems, bias, impacts of invasive species and economic interests are key factors influencing perception and therefore support of management approaches 34 , 35 . Recent research shows disparity between the views of nature experts, users and the general public when it comes to acceptance of invasive species management methods 36 , highlighting the importance of stakeholder engagement in sustainability reporting and robust scientific evaluation of management approaches. By considering the impacts and costs of products used in IAP management across whole life cycles, the sustainability of IAP management methods can be better informed, fostering meaningful alignment with sustainability goals. To determine the wider sustainability of IAP management methods, this study conducted a comparative Life Cycle Assessment (LCA) of Japanese knotweed treatment methods using a long-term, large-scale field trial (Jones et al. 23 ) as a case study. While the products used for invasive plant management have likely been subject to LCA during their formulation, this information is unavailable to the public and there is little comparison of such products in the context of long-term, field-relevant model systems that represent realistic environmental scenarios. This study therefore aims to contribute to this knowledge gap by assessing the environmental impacts of Japanese knotweed control strategies using LCA, and evaluating the relative economic costs to ensure meaningful alignment with sustainability objectives in weed management.

Goal of the life cycle assessment

The goal of this study is to assess and compare the impacts of seven Japanese knotweed management methods during the production phase. The management methods used in this study are based on a long-term study of Japanese knotweed management by Jones et al. 23 and involve chemical treatment using different timings and application rates of glyphosate, picloram and 2,4-D, integrateing physiochemical methods including digging and geomembrane covering. Full details are found in Table 1 . Environmental impacts were modelled and evaluated using the impact indicators provided in the ReCiPe impact assessment method at midpoint (18 categories) and endpoint (3 categories) level 37 (Supplementary Table S1 ). These indicators were used to provide a comprehensive picture on the relative impacts of each treatment. The economic costs to implement each method were also compared across treatments to collectively provide a basis for the evaluation of the implications and practicality of these methods for large-scale knotweed management.

Life cycle assessment scope

This study used a large-scale Japanese knotweed control field trial based in South Wales, UK, as a model system 23 . While the aim of Jones et al. 23 was to assess knotweed treatment efficacy, data was retained on the materials and products used and time consumption per treatment. This provides data to assess the impacts of knotweed management methods at a field-relevant scale. All treatments applied in Jones et al. 23 were used according to manufacturer’s guidelines and are therefore assumed to be representative of treatment methods widely used for invasive plant management in Europe and North America. Treatments were assessed using 225 m 2 field plots, with each treatment replicated in triplicate, allowing most treatments to be assessed over a total area of 675 m 2 , except the covering treatment, which consisted of a single plot (225 m 2 ). As this model system assessed treatment methods over multiple years, data was available to evaluate the long-term impacts of each management approach. Pulling, burning and digging of Japanese knotweed was not assessed in this study as these approaches were considered too costly, labour intensive and could also increase risk of knotweed dispersal 23 .

Treatments selected for LCA

Treatment groups selected for LCA were a sub-set of treatments tested by Jones et al. 23 and were chosen as representative of chemical, physiochemical and physical management methods based on efficacy and current industry recommendations (Table 1 ).

Description of treatment methods used in the LCA

Annual herbicide application data was converted to total herbicide use per hectare (ha) measured as (L ha −1 ) and active ingredient acid equivalent (AE) per hectare (kg AE ha −1 ) (Supplementary Table S2 ). The constituents of each treatment, authorised application rates and actual application rates used by Jones et al. are summarised in Supplementary Table S2 .

Herbicide use for treatment P 2.69, F+SL, S + G 3.60, F, A (Early spring Picloram (Tordon 22 k®) foliar and soil spray and Autumn Glyphosate (Glyfos ProActive®) foliar spray) could not be measured from 2015 onwards as the use of picloram (the active ingredient in Tordon 22 K®) was restricted in the EU. Therefore, the actual amount of herbicide used was assessed, as well as projected values of total herbicide used if the use of picloram had not been restricted. Since the application rate for Tordon 22 K® would have remained approximately consistent each year, projected values were obtained by multiplying the amount of herbicide used in year 2 by 3; total application rate therefore included recorded application rates for years 1 and 2 and projected application rates for years 3 to 5. This approach was also applied to treatment D + P 2.69, F+Sl, S + G 3.60,F, A (picloram and glyphosate application).

Chemical knotweed treatment information

As detailed in Jones et al. 23 , herbicides were applied with dye and adjuvant (Topfilm; 1.2 L ha −1 ) using a knapsack sprayer fitted with a 0.75–1.5 m telescopic lance and flat fan nozzle. Prior to initial soil application of picloram (P 2.69, F+SL , S + G 3.60, F, A ), aboveground Japanese knotweed stem and leaf litter was cleared to facilitate uniform soil coverage and enable herbicide transport to emerging shoots and the rhizome. For stem injection application (G 65.00, ST, A ), in autumn during initial treatment, individual stems were injected with undiluted glyphosate (3–5 ml injection volume; equivalent to 65.00 kg AE ha −1 ). Adjuvant was not included for stem injection. In subsequent years, foliar spray application of glyphosate (3.60 kg AE ha −1 ) was undertaken in autumn.

Integrated physical and chemical methods

For cutting and foliar spray application of glyphosate in autumn (D S + G 3.60, F, A ), Japanese knotweed was cut in the summer using a Stihl FS-450 Professional 2.1 kW clearing saw. Foliar spray application of glyphosate (3.60 kg AE ha −1 ) was performed in autumn, and repeated in subsequent years. Excavation (D S + G 3.60, F, A and D + P 2.69, F+Sl, S + G 3.60, F, A ) was conducted in spring using a JCB 3CX backhoe loader to a depth of 2.5 m, with rhizome material sorted and concentrated at the soil surface by the operator. This was followed by soil spray application of picloram (Tordon; 2.69 kg AE ha −1 ) in spring for P 2.69, F+SL, S + G 3.60,F, A . Both treatments D S + G 3.60, F, A and D + P 2.69, F+Sl, S + G 3.60,F, A received foliar spray application of glyphosate (3.60 kg AE ha −1 ) in autumn. Excavation was only performed in the first year of treatment, though soil and foliar spray application of herbicides continued in following years.

Physical knotweed management

Covering (Mem Cov ) was the only physical management method tested by Jones et al. 23 . Knotweed litter was flattened and left in-situ prior to the emergence of new growth. High-density polyethylene (HDPE) geomembrane (Visqueen® 300 µm 1200 gauge) was placed over the treatment area in early spring and kept in position for the duration of the experiment. Knotweed growth beneath the membrane was flattened and visible emergence round the covering was hand pulled and left under the membrane.

System boundaries and functional unit

This LCA covers the production stage of seven Japanese knotweed treatment methods (Table 1 ; Fig. 1 ). The system boundary includes active ingredient manufacturing with material and energy inputs, production of inert ingredients and mixing, blending and dilution of herbicide active ingredient with inert ingredient to create herbicide products. Production and transport of co-formulates (i.e., tallow amine) and packaging of herbicides are also included within the system boundaries. Herbicide application equipment (e.g. knapsack sprayers) were omitted from this study as they were common to all chemical treatment methods and it was not considered to directly contribute to impacts in knotweed management as they are re-usable. Spray additives (e.g. Topfilm®) were also omitted from this LCA as there is insufficient data relating to their production.

General system boundaries for this comparative LCA. Composition of each treatment is detailed in Table 2 .

The functional unit in this study is the application of 1 ha of Japanese knotweed control treatments over a 5-year period. This functional unit was chosen as it reflects established knowledge of practical treatment of aboveground knotweed growth at a field-relevant spatial scale 23 .

Data inputs

Material inputs for each treatment method (converted to kg ha −1 ) were calculated from long-term records maintained as part of on-going Japanese knotweed control field trials (Table 2 ). Tallow amine ethoxylate is a co-formulant commonly used in glyphosate-based formulations that is present as 9% w/w in Glyfos ProActive®. The ratio of glyphosate to tallow amine was calculated to be 4.58:1 from the product labels of herbicides used in Jones et al. 23 . This was used to calculate the amount of tallow amine used per treatment group (Eq. ( 1 ))

Petrol and diesel inputs were related to the use of machinery for digging and cutting vegetation in physiochemical treatments (Table 2 ).

Data from Life Cycle Inventory (LCI) databases Agri-footprint (Blonk Sustainability, Netherlands) and EcoInvent 3 (Ecoinvent, Switzerland) were used for upstream production processes (Supplementary Table S3 ). These databases can be used to model environmental impacts based on robust, quantitative data. Compatibility and consistent methodological approaches were checked across the databases before use to ensure the validity of the results produced. Specific materials and processes used in SimaPro are shown in Supplementary Table S3 .

LCA impact assessment (LCIA)

The impacts of each treatment method were compared using the ReCiPe 2016 Midpoint and Endpoint LCIA method 37 in SimaPro 9.0.0.48 PhD (Pré Sustainability, Netherlands). The hierarchist (H) impact assessment method was used at both midpoint (problem-oriented, 18 impact categories) and endpoint (damage-oriented, 3 impact categories) assessment levels. The hierarchist approach is based on scientific consensus of appropriate timescales and plausibility of impact mechanisms 37 ; the timescale adopted in evaluating impacts using this approach is 100 years. Sensitivity analysis was conducted to determine whether impact assessment method influenced the results. Values of impacts calculated for the eight knotweed management approaches assessed across three common impact categories calculated by ReCiPe 2016, ILCD 2011 midpoint + V1.10 and EF 3 were found to be non-normally distributed and were compared using a one-sided Kruskal–Wallis test to determine significant differences. Statistics and graphical presentation were conducted in R 3.4.3 38 using the package ggplot2 39 .

Economic evaluation

The economic evaluation focuses on the costs of implementing Japanese knotweed treatments. Costs were assessed under the functional unit of the LCA (i.e., they are evaluated as £ ha −1 5 yrs), though production costs were not calculated due to the number of materials used in herbicide production. The economic evaluation included material costs, time spent per treatment, fuel costs for implementing treatments and labour costs. Inflation and higher fuel costs (e.g. travel to site) were excluded as these costs commonly affect all treatments and therefore are not expected to influence interpretation of relative costs across treatment methods.

Economic evaluation of the treatment methods included prices of packaged products (GBP£) collected from Agrigem Ltd (Supplementary Table S4 ). The price of Monsanto Amenity Glyphosate was used in lieu of Glyfos Proactive® as this product was withdrawn from UK use in 2018. The mean price of Icade® and Synero® was used as a proxy for Tordon 22 K which was deregulated in 2015, as these products most closely resemble Tordon 22 K. The price of Visqueen HDPE geomembrane was obtained from the Visqueen website. Fuel costs are omitted here as it is included in costs of machine operation. Data for time consumption (hours) per treatment was collated from field records and converted to time (hrs) ha −1 per year (Table 3 ).

The time spent on physical components of Japanese knotweed treatments was also recorded and collated (Table 4 ).

Time consumption data was used to calculate labour costs based on representative salaries for weed control practitioners, confirmed by specialist amenity weed management contractor Complete Weed Control Ltd. For excavation, costs of machine hire and labour are combined and based on a 10-h working day (information obtained from Marlay Project Management Ltd; Supplementary Table S5 ).

Material costs, time spent per treatment and labour costs were calculated per ha per treatment to align with the functional unit. Although this study spans 5 years (per the functional unit), inflationary costs and cost fluctuations are not included.

Integration of LCA with economic evaluation

The economic costs of endpoint environmental impacts calculated by LCA can be monetised using conversion factors. As environmental impacts inherently incur economic costs, the total costs per treatment were calculated, to better inform the economic impacts of Japanese knotweed treatment methods. This could contribute to informing costs that can be mitigated during the development of plant protection products and approaches. There are three endpoint impact categories: human health (disability-adjusted life years, DALYs), ecosystems (lost species-year) and resource use (US dollars). The conversion factors used in this study follow Ögmundarson et al. 40 where the conversion factor for human health is 100,000 USD/DALY, and 65,000 USD/species.yr for impacts to ecosystems.

Costs of environmental impacts are calculated using the following Eq. ( 2 ) 41 :

where ${ED}_{i}$ is the environmental impact assessment results and ${m}_{i}$ is the conversion factor for the i th damage category of the LCIA 41 . Once converted from impacts to costs (USD), this was converted to GBP for consistency. The total costs per treatment were then calculated using Eq. ( 3 ) 41 :

where ${F}_{c}$ is the total cost per treatment, ${C}_{LCA}$ is the cost of environmental impacts and ${C}_{e}$ is the economic cost of implementing each treatment.

LCA midpoint and endpoint results

Evaluating impacts of knotweed management approaches at midpoint level.

Treatments involving physical methods (D + P 2.69, F+Sl, S + G 3.60,F, A , D + P 2.69, F+Sl, S + G 3.60,F, A(projected) and Mem Cov ) showed the highest impacts in 11 out of 18 impact categories compared to chemical methods (namely, stem injection, G 65.00, St, A ) which made the highest contribution to six categories (Supplementary Table S6 , Fig. 2 ). High Density Polyethylene (HDPE) Geomembrane covering of Japanese knotweed (Mem Cov ) showed the greatest contribution to six out of 18 impact categories (Supplementary Table S6 , Fig. 2 ). Stem injection and geomembrane covering showed the highest contribution to marine ecotoxicity, indicating that the amount of product used in each treatment is an important factor influencing production impacts.

Relative contribution (%) of Japanese knotweed treatment methods to midpoint impact categories using the ReCiPe assessment method. See Table 1 for description of treatments.

Stem injection (G 65.00, St, A ) contributed the most to freshwater ecotoxicity, freshwater eutrophication, land use, marine eutrophication, mineral resource scarcity and water consumption (Supplementary Table S6 , Fig. 2 ). Geomembrane covering (Mem Cov ) exhibited the greatest impacts to human carcinogenic and non-carcinogenic toxicity, ozone formation affecting human health and terrestrial ecosystems and terrestrial ecotoxicity (Supplementary Table S6 , Fig. 2 ).

Excavation integrated with spraying (D + P 2.69, F+Sl, S + G 3.60,F, A and D + P 2.69, F+Sl, S + G 3.60,F, A(projected) ) contributed the greatest to fine particulate matter emissions, fossil resource scarcity, global warming, ionizing radiation, stratospheric ozone depletion and terrestrial acidification (Supplementary Table S6 ; Fig. 2 ). Digging and turning of knotweed integrated with glyphosate spray (D S + G 3.60, F, A ) was frequently the next greatest contributor to these categories.

No treatment involving foliar herbicide application alone made the greatest contribution to any category (Supplementary Table S6 ; Fig. 2 ). Glyphosate foliar spray (G 3.60, F, A and G 2.16, F, S+A ) had the lowest impacts across 10 impact categories (Supplementary Table S6 , Fig. 2 ). The impacts of bi-annual glyphosate foliar spray (G 2.16, F, S+A ) were 1.1 × greater than single annual glyphosate application (G 3.60, F, A ) (Supplementary Table S6 ).

Integrated picloram and glyphosate application (P 2.69, F+Sl, S + G 3.60, F, A and P 2.69, F+Sl, S + G 3.60, F, A(projected) ) exhibited consistently higher impacts than glyphosate application alone (G 3.60, F, A and G 2.16, F, S+A ) (Supplementary Table S6 , Fig. 2 ). Integrated 2,4-D and glyphosate foliar application (D 2.80 + G 2.16; F, S+A ) exhibited greater impacts to global warming, ionizing radiation, and terrestrial acidification than glyphosate and picloram application (P 2.69, F+Sl, S + G 3.60, F, A and P 2.69, F+Sl, S + G 3.60, F, A(projected) ) and glyphosate application alone. This suggests 2,4-D production has greater impacts to these categories than other herbicides. However, D 2.80 + G 2.16; F, S+A had the lowest impacts to freshwater ecotoxicity and eutrophication, human carcinogenic and non-carcinogenic toxicity, marine ecotoxicity, mineral resource scarcity, terrestrial ecotoxicity and water consumption (Supplementary Table S6 , Fig. 2 ).

Evaluating use of impact assessment method: results of sensitivity analysis

The results for climate change, ozone depletion and freshwater eutrophication were consistent across impact assessment methods (Fig. 3 ). Impacts to marine eutrophication were significantly lower for ReCiPe (H = 19.4, df = 2, p < 0.005), and calculations for water use were significantly greater using the EF 3 assessment method (H = 25.8, df = 2, p < 0.005) (Fig. 3 ). This suggests impacts to marine eutrophication and water use may be underestimated using the ReCiPe method.

Sensitivity analysis of common impact categories (n = 3) across ReCiPe, ILCD and EF 3.0 impact assessment methods for the eight knotweed management approaches assessed in this LCA. In the box plots the center line = median; box limits = upper and lower quartiles; whiskers = 1.5 × interquartile range; points = outliers.

Evaluating endpoint impacts of knotweed management

Excavation followed by picloram and glyphosate foliar spray (D + P 2.69, F+Sl, S + G 3.60, F, A(projected) and (D + P 2.69, F+Sl, S + G 3.60, F, A ) revealed the greatest impacts in most endpoint categories (Supplementary Table S7 , Fig. 4 ). Glyphosate stem injection (G 65.00, St, A ) and projected physiochemical methods (D + P2.69, F+Sl, S + G 3.60,F, A(proj) ) exhibited the two greatest impacts to ecosystems. Geomembrane covering (Mem Cov ) incurred the greatest economic impact (Supplementary Table S7 , Fig. 4 ). Glyphosate foliar spray treatments (G 3.60, F, A and G 2.16, F, S+A ) had the lowest impacts to most endpoint categories. Chemical treatments involving picloram (P 2.69, F+Sl, S + G 3.60, F, A ) had greater impacts to resource use than glyphosate stem injection, highlighting differences in the production of these herbicides.

Relative impacts and economic cost of Japanese knotweed treatment methods at endpoint level. See Table 1 for description of treatments.

Economic evaluation of knotweed management approaches

Geomembrane covering (Mem Cov ) incurred the greatest total costs (costs to implement treatment and cost of environmental impacts), followed by physiochemical methods (D + P 2.69, F+Sl, S + G 3.60,F, A(projected ; D + P 2.69, F+Sl, S + G 3.60,F, A , and D S + G 3.60, F, A ,), and treatment involving picloram (P 2.69, F+Sl, S + G 3.60, F, A(projected) ; P 2.69, F+Sl, S + G 3.60, F, A ) (Supplementary Table S7 , Fig. 4 ). Glyphosate treatments incurred the lowest costs (G 3.60, F, A ,; G 2.16, F, S+A ; D 2.80 + G 2.16; F, S+A and G 65.00, St, A ; Supplementary Table S7 , Fig. 4 ). Costs to implement treatment methods (including material and labour) accounted for 95.5% ± 2.8 of costs per treatment, mainly made up by labour costs due to the time taken to implement each treatment.

Comparison of time consumption across treatment methods

Geomembrane covering (Mem Cov ) had the greatest time consumption (2,666.7 h ha −1 ; Fig. 5 ) due to the time taken to install geomembrane and repeated hand-pulling of emergent Japanese knotweed emerging around the membrane. Due to the need for vegetation clearance, treatments involving picloram and glyphosate spray (P 2.69, F+Sl, S + G 3.60, F, A and P 2.69, F+Sl, S + G 3.60, F, A(projected) ) exhibited the second-highest time consumption (378.8 and 452.9 h ha −1 , respectively; Fig. 5 ).

Time taken to implement each treatment (collated from records of study system 23 ). See Table 1 for description of treatments.

The aim of this study was to compare the sustainability of Japanese knotweed treatment approaches at a field-relevant scale using empirical data from a large-scale, long-term project. This information is intended to inform management decisions and contribute to our understanding of the relative impacts of physical and chemical management methods.

The relative contribution to impact categories under the ReCiPe hierarchist method and economic costs of implementing these treatments were used to determine the most economically and environmentally viable options. The modelled impacts are based on the hierarchist approach to LCIA which uses a timescale of 100 years 30 . We found the simplest methods elicited the most favourable environmental outcomes. Foliar spray glyphosate application produced the lowest relative impacts, economic costs and time consumption as it is the most effective treatment against Japanese knotweed 23 , 42 . By aligning knotweed management with plant biology and ecophysiology, effective control can be achieved with relatively low doses of glyphosate 23 . Differences between foliar spray (G 3.60, F, A & G 2.16, F, S+A ) and stem injection (G 65.00, St, A ) arise from the larger application rate and concentration of glyphosate used in stem injection 43 , 44 , illustrating that environmental impacts increase with herbicide application rate. Foliar spray methods offer fewer negative impacts as the glyphosate is diluted into a spray mix applied at relatively low concentrations. As Japanese knotweed incurs some of the highest costs of all invasive species in the UK 4 , 45 , primarily owing to management, the results of this study may inform cost-effective management.

Differences in the impacts of integrated foliar application of 2,4-D and glyphosate (D 2.80 + G 2.16; F, S+A ) compared to glyphosate alone highlight discrepancies in emissions resulting from 2,4-D and glyphosate production. Integrated picloram soil and glyphosate foliar application (P 2.69, F+Sl, S + G 3.60, F, A and P 2.69, F+Sl, S + G 3.60, F, A(projected) ) had greater midpoint and endpoint impacts than glyphosate and lower impacts than physiochemical methods (D S + G 3.60, F, A & D + P 2.69, F+Sl, S + G 3.60,F, A ; Figs. 2 and 4 ), emphasising the simplest control methods elicited the lowest impacts. In terms of control success, picloram produces mixed results in knotweed management 46 and is less effective than glyphosate alone 23 .

Physical and integrated physiochemical methods exhibited the greatest negative environmental impacts in this study (Figs. 2 and 4 ). The impacts of High-Density Polyethylene (HDPE) geomembrane covering of Japanese knotweed (Mem Cov ) arise from crude oil extraction, distillation, cracking and extrusion processes involved in plastic manufacture which are resource and energy intensive and produce substantial emissions 47 , 48 , 49 . This is evident from the LCA results for Mem Cov (Supplementary Table S6 ). Geomembrane covering also had the greatest total economic costs (Fig. 4 ), owing to the costs and time consumption associated with implementing this treatment (Fig. 5 ). This is highlighted by Rask et al. 50 who found less effective physical methods require more intense treatment to achieve levels of control equivalent to herbicide application. In this model study, covering was an ineffective management strategy against Japanese knotweed at field scale 23 .

The impacts of integrated physiochemical Japanese knotweed management (D S + G 3.60, F, A and D + P 2.69, F+Sl, S + G 3.60,F, A ) arise from the use of diesel for excavation. Modelled impacts of knotweed excavation to ozone depletion resulting from crude oil extraction and distillation (associated with diesel production) and fuel combustion is consistent with literature on the impacts of soil remediation techniques 51 . Physiochemical methods also caused the greatest endpoint impacts (Fig. 4 ), however, time consumption was consistent with foliar spray methods (Fig. 5 ). While these treatments were less effective than glyphosate application alone 23 , excavation is often used where timescales may not allow for extended treatment by annual herbicide application and the cost of excavation is offset by the costs incurred through project delay (e.g. high value land development sites) 24 , 46 . Physical disruption by rhizome tillage may deplete plant energy reserves and accelerate control of aboveground growth 23 . However, the costs, labour requirements and need for disposal of controlled waste linked to this method are disadvantageous 24 , 46 . This approach may also pose a biosecurity risk through accidental dispersal of knotweed rhizome fragments.

The relative impacts of excavation versus herbicide application should be considered in relation to site-specific management objectives and available resources. Objectives prioritising biodiversity conservation, effective knotweed management and environmental sustainability may favour targeted, long-term approach. In this case, herbicides are an effective management tool 52 , though careful consideration of post-application impacts and wider ecological context is needed. Where the costs of management outweigh the impacts of Japanese knotweed, a do-nothing approach may be more sensible than employing alternative physical methods, which are less effective and elicit greater production impacts.

Post-application impacts of Japanese knotweed management methods

The relative impacts of invasive plant management methods post-treatment are currently unknown. Research on the environmental fate of herbicides mainly focuses on agricultural settings as the primary consumer of herbicides. The presence of pesticide residues in agricultural soils is now the norm 53 ; glyphosate residues have been detected in the wider environment 54 , 55 , food products 56 and human populations 57 , 58 , 59 . A recent meta-analysis has found that cumulative exposure to glyphosate-based herbicides is associated with increased risk of non-Hodgkin lymphoma 60 ; however, a prospective cohort study found that glyphosate was not statistically significantly associated with cancer at any site 61 . Other toxic effects reviewed by Mesnage et al. 62 have also been found, though the European Food Safety Authority (EFSA) concluded evidence for its classification as “probable carcinogenic” was limited 63 , 64 .

Exposure to glyphosate is proposed to negatively affect hormone activity, cell and organ functioning in birds, fish and mammals exposed to high doses and chronic cumulative low doses 65 , 66 , 67 and imposes selection pressure towards herbicide-tolerance in plants 65 . However, the ecological interactions of herbicide residues are complex 68 . Impacts to microbial communities are limited 69 as microbes readily degrade residues 70 . Co-formulants in herbicide products also impose risks to human and ecological health 62 , 71 . This has been further confirmed by Straw et al. 72 who concluded co-formulants in Roundup® were the cause of bee mortality, rather than the active ingredient. Conversely, Weidenmüller et al. 73 recently found that sub-lethal exposure to glyphosate alone can reduce thermoregulation in bumblebees during periods of stress. While these studies provide valuable information on the hazards of exposure, studies under field conditions using field-relevant glyphosate concentrations would broaden our understanding.

Physical approaches to IAP management may be considered less damaging than herbicides but are associated with fossil fuel use (at large scales where hand-pulling or cutting is not feasible), contributing to a key driver of carbon emissions. Records of emissions associated with transport, disposal or encapsulation of knotweed-infested soil are limited, all of which exacerbate the impacts of physical management approaches. Conversely, herbicides may reduce the environmental impacts of agricultural weed control by minimising carbon dioxide (CO 2 ) emissions associated with fuel use for physical or mechanical weed management 74 . With global commitment to reducing emissions in line with the Paris Agreement 75 , evaluation of the wider impacts of plant protection products is needed. This can provide further insight on the relative importance of environmental impacts arising from production versus use and end-of life life-cycle stages.

Costs versus benefits in IAP management

The mismatch between production and post-application impacts of Japanese knotweed management methods emphasises that more investigation and dialogue around the relative costs and benefits of IAP management is needed. The widespread prevalence of herbicide residues is irrefutable and evidence of risk of exposure to these compounds is growing, leading to calls for stricter herbicide regulation 2 . However, without careful comparison of chemical versus physical methods across entire lifecycles, our ability to make informed decisions around IAP management remains limited. We do note cradle-to-grave assessment of environmental impacts in this study was limited by a paucity of data on field-relevant environmental release pathways of products used for IAP management. Future effort to gather this information would be welcomed.

While wider sustainability is a vital goal for IAP management methods, the methods we employ must also be effective. For select invasive plants, including Japanese knotweed, chemical treatment is a mainstay 3 , 23 , though no method currently results in complete eradication. Unlike the global use of herbicides for agriculture, invasive plant management is rooted in nature conservation and sustainability 3 and operates at smaller scales. The need for herbicides versus alternative (often untested) weed management products must therefore be informed by appropriate context and wider goals. Social perceptions of IAP management methods are an important part of this 33 but should also be informed by empirical evidence at appropriate scale, considering the social impacts of knotweed infestation and subsequent management. From a socio-economic perspective, this study indicates that employing the most effective and sustainable approach for knotweed management is also the most cost-effective approach. Moreover, at a time where social and ethical responsibility for the environment is increasing, considering the bigger picture of IAP management methods can help prioritise these approaches. The results of this study may be used to initiate dialogue around the relative impacts and sustainability of IAP management methods and how this compares to public perceptions.

Whether the long-term impacts of plant invasions outweigh the effects and opinions of management also needs consideration to inform value- and goal-driven decisions at a strategic scale 28 . If the costs of management outweigh the benefits, efficacy, economic viability and impacts across entire lifecycles must be considered when selecting alternative treatments or appropriate mitigation methods. Integrating the impacts of invasive plants with Life Cycle Assessment of management scenarios to compare treatment with a ‘do nothing’ approach is recommended to address this. Stakeholder engagement in this matter is therefore vital if we aim to align with sustainability goals.

Conclusions

This study assessed the environmental and economic impacts of eight management approaches for Japanese knotweed. Glyphosate foliar spray methods found to be the most effective against Japanese knotweed by Jones et al. 23 elicited the fewest environmental and economic impacts, illustrating methods that ultimately reduced input gave better outcomes. Parsimony should therefore be an important consideration when making management decisions. Geomembrane covering imposed the greatest impacts during production and largest economic costs, followed by integrated physiochemical (excavation and herbicide application) methods. While post-treatment impacts of knotweed management methods are a current knowledge gap, evidence of the wider implications of herbicide formulations and the products and processes used in physical management methods is growing 53 , 57 , 62 , 76 . These results therefore underscore the need for careful (and comprehensive) consideration of risks and benefits associated with invasive plant management processes when devising invasive plant management strategies at scale 28 .

Data availability

The data generated and analysed in this study are available from the corresponding authors on reasonable request.

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Acknowledgements

This article was derived from a Knowledge Economy Skills Scholarships (KESS II) Ph.D. studentship part-funded by the Welsh Government’s European Social Fund (ESF) convergence programme, and partnered with Complete Weed Control LTD.

This work was part-funded by the European Social Fund (ESF) through the European Union’s Convergence programme administered by the Welsh Government with Swansea University and Complete Weed Control Ltd.

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S.H. conceptualised and conducted the project and prepared the first draft and revisions of the manuscript. D.J. conceptualised and provided data for this study. T.T. conducted the study, provided technical support and advised on project. I.G. provided advice and validated economic cost data. D.E. conceptualised and supervised the project. All authors contributed to manuscript preparation and review.

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Hocking, S., Toop, T., Jones, D. et al. Assessing the relative impacts and economic costs of Japanese knotweed management methods. Sci Rep 13 , 3872 (2023). https://doi.org/10.1038/s41598-023-30366-9

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New Approaches on Japanese Knotweed ( Fallopia japonica ) Bioactive Compounds and Their Potential of Pharmacological and Beekeeping Activities: Challenges and Future Directions

Affiliations.

1 Faculty of Animal Science and Biotechnology, University of Animal Sciences and Veterinary Medicine Cluj-Napoca, 400372 Cluj-Napoca, Romania.
2 Faculty of Geography, Babeş-Bolyai University, 400084 Cluj-Napoca, Romania.
3 Faculty of Geodesy, Technical University of Civil Engineering Bucharest, 020396 Bucharest, Romania.
4 Faculty of Horticulture, University of Animal Sciences and Veterinary Medicine Cluj-Napoca, 400372 Cluj-Napoca, Romania.
5 Faculty of Veterinary Medicine, University of Animal Sciences and Veterinary Medicine Cluj-Napoca, 400372 Cluj-Napoca, Romania.
6 Department of Agricultural Sciences, University of Naples "Federico II", Via Università, Portici, 100-80055 Naples, Italy.
PMID: 34961091
PMCID: PMC8705504
DOI: 10.3390/plants10122621

Known especially for its negative ecological impact, Fallopia japonica (Japanese knotweed) is now considered one of the most invasive species. Nevertheless, its chemical composition has shown, beyond doubt, some high biological active compounds that can be a source of valuable pharmacological potential for the enhancement of human health. In this direction, resveratrol, emodin or polydatin, to name a few, have been extensively studied to demonstrate the beneficial effects on animals and humans. Thus, by taking into consideration the recent advances in the study of Japanese knotweed and its phytochemical constituents, the aim of this article is to provide an overview on the high therapeutic potential, underlining its antioxidant, antimicrobial, anti-inflammatory and anticancer effects, among the most important ones. Moreover, we describe some future directions for reducing the negative impact of Fallopia japonica by using the plant for its beekeeping properties in providing a distinct honey type that incorporates most of its bioactive compounds, with the same health-promoting properties.

Keywords: Fallopia japonica; Japanese knotweed; antimicrobial activity; antioxidant effect; bioactive compounds; honey; invasive species; phytopharmaceuticals.

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Japanese knotweed is no more of a threat to buildings than other plants – new study

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Japanese knotweed, a widespread invasive non-native species in the UK, is seldom out of the news and can strike fear into the hearts of anyone who finds it growing on their property, house owner or developer alike. It is a tall, herbaceous and fast-growing plant that reduces biodiversity and can increase the risk of flooding.

Japanese knotweed – Fallopia japonica – is associated with a significant economic burden in the UK. Recently, a court in Wales ruled that homeowners were entitled to claim damages from Network Rail because rhizomes (the plant’s underground shoots) had extended below their properties. Japanese knotweed is subject to various legislation and mortgage lenders often require that an insurance-backed management plan for the plant is in place when it is present on or near a property before agreeing to a mortgage. The presence of the species can also result in a reduction of a property’s value.

Japanese knotweed’s often quoted abilities to grow through concrete, damage buildings and extend destructive rhizomes seven metres from the above ground portion of the plant are among the most feared features of the plant. But it is exactly these supposed abilities that our new research challenges.

I teamed up with lead author Mark Fennell and co-author Max Wade, both members of the environment and ground engineering team at global services firm AECOM, to present the most comprehensive study to date assessing the ability of Japanese knotweed to cause damage to built structures compared to other plants. What we found is at odds with what is currently accepted and may help to alleviate fears that the plant can grow through concrete or cause major structural damage to buildings.

There are three primary ways plants can damage buildings: indirect damage though subsidence or heave; direct damage though collapse and impact; and direct damage through the accumulated pressure of plant growth. We assessed the evidence that Japanese knotweed can cause each of these types of damage and how the possibility of Japanese knotweed causing damage in these ways compares to other plants.

A detailed survey of the literature revealed that indirect damage caused by plants is only possible on shrinkable clay soils, a type of soil that is not particularly common in the UK . Even where the most shrinkable soils are found, the biology and size of Japanese knotweed makes it less likely to facilitate this type of damage than large trees. This means that the risk of Japanese knotweed causing damage by modifying soil water content is extremely remote and only relevant in areas with exactly the right type of soil.

Seven-metre rule

Our next step was to conduct a survey of members of the Property Care Association and Royal Institution of Chartered Surveyors who have been involved in property surveys and treating or removing Japanese knotweed in the UK. Respondents were asked to report whether they had observed damage to buildings occurring with Japanese knotweed.

Only between 2% and 6% of respondents reported any co-occurrence of Japanese knotweed and structural damage to buildings. Our paper also concluded that where Japanese knotweed is associated with damage, it is likely that the plants will have exacerbated existing damage, rather than being the initial cause of the damage.

Further to this, we asked respondents to report the lateral extension of underground shoots in cases where they had undertaken full excavations of Japanese knotweed. This allowed us to test the “seven-metre rule” commonly used to denote whether Japanese knotweed is likely to pose a threat to buildings.

We found that smaller stands of Japanese knotweed (less than four square metres in area) generally had rhizomes no longer than two metres and not beyond four, while 75% of larger stands had rhizomes extending no further than 2.5 metres. We received only one report of rhizomes over four metres in length. This shows that the fear of Japanese knotweed commonly having seven-metre rhizomes is unfounded and the use of the seven-metre rule is not robust for determining the likely lateral extent of these underground shoots.

We then assessed 68 abandoned properties on three streets in northern England with a significant Japanese knotweed infestation, to determine whether these houses had damage caused by the presence of the plant. Many properties had Japanese knotweed present or nearby but we found no evidence to suggest that the dilapidation of the properties was caused by the plant. In fact, the other plants – particularly some woody trees – were visually associated with more damage. This area represented a near worst case scenario for houses that had been left to the mercy of Japanese knotweed and still we found no evidence for the plant causing damage.

Overall, our study found no support for the commonly suggested ideas that Japanese knotweed routinely damages buildings and that its influence extends seven metres from plants above ground. Nor did we find evidence that it poses a major risk to built structures.

Japanese knotweed remains a serious threat to Britain’s biodiversity, ecosystems and the amenity value of land, but these very real threats should not be confused with what our research shows to be myth more than fact. Japanese knotweed is no more of a risk to solidly built homes and buildings than many plants and less so than many woody species, particularly some large trees.

Read more: We've found the best way to control Japanese knotweed

Our research highlights that the key to tackling invasive species lies in developing a detailed understanding of their biology and further highlights the ongoing need for new research and knowledge to help us to understand and, hopefully, address the emerging challenges presented by invasive non-native species.

Invasive species
Japanese knotweed

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Optimising physiochemical control of invasive Japanese knotweed

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Daniel Jones ORCID: orcid.org/0000-0002-3192-6450 1 , 2 ,
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Mike S. Fowler ORCID: orcid.org/0000-0003-1544-0407 1 ,
Rhyan Law-Cooper 1 , 2 ,
Ian Graham 3 ,
Alan Abel 4 ,
F. Alayne Street-Perrott ORCID: orcid.org/0000-0003-1149-9110 5 &
Daniel Eastwood ORCID: orcid.org/0000-0002-7015-0739 1

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Japanese knotweed, Fallopia japonica var. japonica , causes significant disruption to natural and managed habitats, and provides a model for the control of invasive rhizome-forming species. The socioeconomic impacts of the management of, or failure to manage, Japanese knotweed are enormous, annually costing hundreds of millions of pounds sterling (GBP£) in the UK alone. Our study describes the most extensive field-based assessment of F. japonica control treatments undertaken, testing the largest number of physical and/or chemical control treatments (19 in total) in replicated 225 m 2 plots over 3 years. Treatments focused on phenology, resource allocation and rhizome source–sink relationships to reduce the ecological impacts of controlling F. japonica . While no treatment completely eradicated F. japonica, a multiple-stage glyphosate-based treatment approach provided greatest control. Increasing herbicide dose did not improve knotweed control, but treatments that maximised glyphosate coverage, e.g., spraying versus stem injection, and exploited phenological changes in rhizome source–sink relationships caused the greatest reduction of basal cover and stem density after 3 years. When designing management strategies, effective control of F. japonica may be achieved by biannual (summer and autumn) foliar glyphosate applications at 2.16 kg AE ha −1 , or by annual application of glyphosate in autumn using stem injection at 65.00 kg AE ha −1 or foliar spray at 3.60 kg AE ha −1 . Addition of other herbicides or physical treatment methods does not improve control. This work demonstrates that considering phenology, resource allocation and rhizome source–sink relationships is critical for the control of invasive, rhizome forming species.

Assessing the relative impacts and economic costs of Japanese knotweed management methods

Controlling perennial pepperweed (lepidium latifolium) in a brackish tidal marsh.

Developing effective management solutions for controlling stinking passionflower (Passiflora foetida) and promoting the recovery of native biodiversity in Northern Australia

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Introduction

Japanese knotweed ( Fallopia japonica var. japonica ; referred to as F. japonica hereon) is one of a number of herbaceous, rhizomatous, non-climbing perennial Fallopia spp., collectively referred to as Japanese knotweed sensu lato ( s.l. ) taxa (Bailey and Conolly 2000 ). Japanese knotweed s.l. are significant Invasive Alien Plants (IAPs) across economically developed countries (Bailey 2013 ; Lavoie 2017 ). Spread is primarily through asexual (clonal) dispersal, encouraged by both anthropogenic and natural disturbance processes (e.g. disturbance by floods), accelerated by suboptimal control methods and disposal of soil contaminated with knotweed rhizome (Dawson and Holland 1999 ; Bailey et al. 2009 ).

F . japonica is a fast-growing competitor (C-strategist; Grime 2001 ) that exhibits highly plastic growth responses to environmental conditions (Beerling et al. 1994 ). It forms rhizomes (perennating woody storage organs), that commonly accumulate late in the preceding growing season, year after year (Callaghan et al. 1981 ). The extensive rhizome network of F. japonica is concentrated in the first metre of the soil profile and may extend vertically to a depth of 4.5 and 20 m laterally from the main stand of aboveground growth (Beerling et al. 1994 ). Above and belowground (dry) biomass values reported in northern Europe (Czech Republic, Germany and UK) range from 0.75–2.53 to 1.19–3.01 kg m −2 , respectively (Callaghan et al. 1981 ; Adler 1993 ; Brock 1995 ; Strašil and Kára 2010 ). Domination of plant communities by dense, monospecific F. japonica stands results from a rapid early season development from shoot clump and rhizome buds that allow pre-emptive occupation of space and resource capture (Grime 2001 ; Lavoie 2017 ). Dominance of non-native plant communities is maintained through the growing season via escape from herbivory i.e. the Enemy Release Hypothesis (ERH; Maurel et al. 2013 ) and direct and/or indirect allelopathy through the soil biota i.e. the mutualism facilitation hypothesis (Parepa et al. 2013 ; Parepa and Bossdorf 2016 ), while resource sharing through clonal rhizome integration may also aid competition and spread (You et al. 2014 ). Such invasions displace native flora, reducing floral assemblages and modify ecosystem functioning, e.g. soil nutrient cycling (Lavoie 2017 ). Socioeconomic impacts include high F. japonica control costs that amount to £165.6 million per annum in the UK alone (Williams et al. 2010 ).

We propose that F. japonica control treatments must account for the linkage between above and belowground tissues to inform the correct timing, concentration and intensity, e.g. rhizome dormancy maybe induced by aboveground herbicide application (Nkurunziza and Streibig 2001 ). The delivery of adequate herbicide into belowground tissues and/or depletion of rhizome reserves are hampered by substantial above and belowground biomass and a deep rhizome system that exhibits a strong seasonal change in source–sink strength.

Management of F. japonica in Europe and North America is predominantly chemical, based on a range of active ingredients promoted (Delbart et al. 2012 ; Clements et al. 2016 ). The principal active ingredient employed is glyphosate, an aromatic amino acid (AAA) synthesis inhibitor, though synthetic auxins and acetolactate synthase (ALS) inhibitors are also widely used (Online Resource 1, Table S1.1). Beyond this, there are a wide range of herbicide application methods recommended for knotweed control, few of which have been tested quantitatively or at an appropriate scale, despite widespread application (Table S1.2).

We therefore tested the three main approaches applied to F. japonica physiochemical control: physical (e.g. covering), chemical (e.g. application of herbicide) and integrated (e.g. cutting before herbicide spraying; Table S1.3; Child and Wade 2000 ). Our study combined F. japonica physiology (i.e. resource allocation and rhizome source–sink strength) with physical or chemical control method target (i.e. resource depletion, uptake, movement and metabolism) to develop a novel, four-stage mechanistic model to test treatment efficacy (Fig. 1 ). Briefly, stage 1; early season, pre knotweed emergence disruption of new aboveground growth and depletion of rhizome reserves. Stage 2, spring treatment against metabolism and growth, reducing resource acquisition. Stage 3, summer treatment at maximum height and leaf expansion, targeting the transition point where the rhizome becomes a reserve. Stage 4, late season coupling of aboveground resource translocation to the rhizome with herbicide application, maximising translocation to belowground tissues.

Four stage mechanistic model of phenological changes in F. japonica growth, resource allocation and rhizome source–sink strength during the growing season. LAI leaf area index. Note linkage of above and belowground growth processes with changes in source–sink strength and that rhizome tissue sink strength increases through the growing season from June, reaching a peak in August–November during flowering and senescence. To maximise physiochemical control outcomes, physical and herbicide control treatment application should account for seasonal changes in rhizome source–sink strength. The precise timing of stages 1–4 are dependent upon local conditions and phenology may vary, impacting upon control (e.g. clones growing at higher altitude will exhibit delayed phenology, relative to lowland clones)

The primary objective of this study was to employ an evidence-based experimental approach to provide a robust, appropriately scaled field assessment of management strategies using F. japonica as a model for rhizome-forming IAPs. We tested 19 currently employed control strategies for effectiveness with the aims of optimising F. japonica control and informing field-scale management of other IAPs. Limited spatial and temporal scales (less than 2 years) of field trials conducted to date have restricted the interpretation of control outcomes and interpretation of the mechanisms underpinning effective control (Child 1999 ; Skibo 2007 ; Delbart et al. 2012 ). Here we report on the most extensive and comprehensive (in terms of control treatments tested), multi-year field trials of F. japonica control, explicitly considering whether targeting the rhizome source–sink switch can provide more effective and sustainable F. japonica control, by reducing pesticide application to minimise ecological impact and maximise habitat recovery (Kettenring and Adams 2011 ).

Field trial site selection

Three sites in south Wales (UK) were selected (Fig. 2 ), with comparable geological and hydrological conditions (Online Resource 2). For the present study, control methods were applied from 2012 to 2014 at sites 1 (Lower Swansea Valley Woods) and 2 (Swansea Vale Nature Reserve) and from 2013 to 2015 at site 3 (Taffs Well).

Map of the study area. a Location of field trial sites in south Wales, UK. Field trial sites are assigned: LS Lower Swansea Valley Woods, SV Swansea Vale Nature Reserve, TW Taffs Well

Experimental design

Fifty-eight 225 m 2 treatment and control plots were established across all three sites (Online Resource 3) and each plot was surrounded by a 1 m buffer zone. Physical, chemical and/or integrated treatments were applied to the whole of each treatment plot. Each treatment group (TG) was replicated in triplicate (with the exception of the covering treatment) and all sites contained one control plot. No dummy treatments were applied to the control plots as no facilities were available to clean the knapsack sprayer tank at field trial site 1 which may have resulted in application of dilute quantities of herbicide, influencing control plot response. Intra- and inter-site assignment of TGs was semi-randomised, as certain herbicide products could not legally be used near watercourses (e.g. picloram; Online Resource 2).

Annual plot assessment was undertaken in spring or autumn before control treatment application and was based on six randomly assigned 4 m 2 monitoring patches within each field trial plot; pre-treatment assessment commenced in 2012. Data captured included: aboveground F. japonica stem density, 4 m 2 ; F. japonica basal percentage cover (%) and whole plant maximum light utilisation efficiency of PSII ( F v / F m ). F v / F m was measured using a chlorophyll fluorescence system (Handy Plant Efficiency Analyser (PEA), Hansatech Instruments, King’s Lynn, UK; light intensity 3000 μmol m −1 s −2 ; dark adaption time calibrated). Mean whole plant F v / F m was derived from leaf measurements taken at 25, 50 and 75% of total plant height (to reflect leaf age); six representative plants were measured within each treatment and control plot.

The above three responses to physical and chemical treatment were assessed to provide a complete picture of F. japonica response, accounting for absolute basal cover reduction, deformed regrowth, potential photosynthetic capacity and whole plant photosynthetic efficiency and physiological state. Importantly, basal cover measurements were made at ground level and recorded deformed regrowth, providing a good indicator of recovery from physiochemical treatments (particularly herbicide). Stem density is a stable measurement throughout the growing period and provides indication of declining aboveground investment by the plant. F v / F m determines photosynthetic and carbon fixation efficiency, while also providing an indication of whole plant stress status (Maxwell and Johnson 2000 ; Dayan and Zaccaro 2012 ).

Herbicide product selection and control treatment timing

Herbicide product selection and application timing of the 19 treatments (Table 1 ) was based upon biological understanding of F. japonica source–sink relationships (Fig. 1 ) and existing, untested control treatments reported in the literature (Online Resource 1). The novel inclusion of a PPO inhibitor (HRAC Group E; WSSA Group 14) within the experimental design is the first time that the efficacy of this herbicide group has been reported for F. japonica control in the scientific literature (Online Resource 4, Table S4.1 provides herbicide product physical properties, fields of use, legal designations and UK inclusion date; Table S4.2 provides herbicide product and spray adjuvant manufacturers and suppliers).

Details of control treatments

Herbicide control treatments, soil and foliar spray application (tgs a1 to a13, site 3).

Herbicide product(s) were applied at a fixed rate (L or g ha −1 ), with consistent application of active ingredient(s) per unit area using a Cooper Pegler CP3 (20 L) Classic knapsack sprayer, fitted with a 0.75–1.5 m telescopic lance and Cooper Pegler blue flat fan nozzle (AN 1.8). All soil and foliar spray application herbicide products were applied with dye and adjuvant (Topfilm; 1.2 L ha −1 ) to ensure even coverage and maximise herbicide active ingredient absorption. Herbicide products containing aminopyralid (Synero, synthetic auxin) were applied with antifoaming agent (Foam Fighter). Weather forecast information was consulted to ensure that no rain was forecast for a minimum of 8 h post-application. Prior to initial soil spray herbicide application of picloram and flazasulfuron (TGs a8 and a12), aboveground F. japonica material from previous years, including dead stems and litter was cleared to ensure even coverage of the substratum and facilitate herbicide delivery to the rhizome and emerging shoots.

Cut and fill application (TG b1, site 3)

In autumn (stage 4) of the first year of treatment, individual stems were cut at the second node above ground level, with variable rate application of 50% v/v glyphosate solution per stem (5–10 ml dose/stem; equivalent to 87.12 kg AE ha −1 ), using a Cooper Pegler CP3 knapsack sprayer, standard lance and green anvil nozzle (AN 1.2—anvil removed). Adjuvant (1.2 L ha −1 ) was included in the tank mix to maximise active ingredient absorption. Cut stems were left in situ to prevent dispersal of F. japonica propagules. In subsequent years, foliar spray application of glyphosate at full label rate (FR; 3.60 kg AE ha −1 ) was undertaken in autumn.

Stem injection application (TG c1, site 3)

In autumn (stage 4) of the first year of treatment, each individual stem was injected at the second node above ground level, with variable rate application of undiluted glyphosate per stem (3–5 ml injection volume; equivalent to 65.00 kg AE ha −1 ), using a Nomix Enviro Stem Master injection system. Adjuvant was not included in the injection system to minimise the likelihood of blockage. In subsequent years, foliar spray application of glyphosate at FR (3.60 kg AE ha −1 ) was undertaken in autumn.

Integrated physiochemical control treatments

Cutting and foliar spray application of glyphosate in autumn (tg d1, site 3).

F . japonica was cut in mid growing season (summer; stage 3) to promote stand access and maximise re-growth. Cutting was performed using a Stihl FS-450 Professional 2.1 kW clearing saw and foliar spray application of glyphosate at FR (3.60 kg AE ha −1 ) was undertaken in autumn (stage 4). In subsequent years, foliar spray application of glyphosate at FR (3.60 kg AE ha −1 ) was undertaken in autumn.

Excavation (TGs d2 and d3, site 1)

Excavation was undertaken in spring (stage 1) using a JCB 3CX backhoe loader (94 cm bucket, 0.3 m 3 capacity) to a depth of 2.5 m, with rhizome material roughly sorted and concentrated at the soil surface by the heavy equipment operator. For TG d3, this was immediately followed by soil spray application of picloram at FR (Tordon; 2.69 kg AE ha −1 ) in spring and for both TGs d2 and d3, foliar spray application of glyphosate at FR (3.60 kg AE ha −1 ) was undertaken in autumn (stage 4). In subsequent years, excavation was not performed, though soil and foliar spray application of herbicides was maintained.

Physical control treatments

Covering combined with hand pulling (tg d4, site 2).

Prior to covering in early spring (stage 1), aboveground F. japonica material from previous years was flattened and left in situ. High-density polyethylene (HDPE) geomembrane (Viqueen ® 300 μm 1200 gauge) was extended over the treatment area and weighted to remain in position for the duration of the experiment. Subsequent F. japonica growth beneath the membrane was flattened, while visible growth emerging around the covering was hand pulled and left in situ underneath the membrane, to prevent dispersal of F. japonica propagules. Covering was the only physical control treatment trialled, as other physical control treatments (pulling, digging and burning) were considered too costly, labour intensive and increased the risk of F. japonica spread.

Data analysis

F. japonica basal cover (%; 4 m 2 ) data was arcsine transformed prior to analysis (Sokal and Rohlf 1981 ). We used Akaike information criteria (AIC) to select the best performing model from the following four candidate models, applied to each response variable ( y ) for independent comparison across time ( t ) at each site ( i ):

where days after treatment (DAT) is a continuous variable indicating the days after the first treatment was applied and treatment group (TG) is a categorical variable indicating the treatment group applied (including the control). The DAT t *TG i term indicates the interaction term between time and treatment.

Inference was based on the parameters estimated from the best performing candidate model(s) at each site (Burnham and Anderson 2002 ). We used general linear (ANCOVA design) models to analyse arcsine transformed % basal cover and F v / F m response data and compared Poisson and Negative Binomial generalised linear models (GLMs) for the stem density response data, considering AIC and goodness-of-fit statistics (comparing residual model deviance with degrees of freedom using a χ 2 -test) for the GLMs. In all cases, the Negative Binomial GLM was a more appropriate model, with the Poisson GLMs consistently being overdispersed, showing a significant difference between residual deviance and d.f. ( p < 0.001). Therefore, only results based on the negative binomial GLMs are presented here.

Within-site comparison of the ‘best’ predicted treatments at each site with other treatments and respective site controls were made based upon prior knowledge of biological and treatment processes. At site 1, TG d3 (spring dig; spring picloram FR; autumn glyphosate FR) was compared with TG d2 and the control; at site 2 TG d4 (covering) was compared with the control and at site 3 TG a3 (summer and autumn glyphosate half full label rate (HR) foliar spray) was compared with all other TGs and the untreated control.

All data were analysed using R v3.2.5 (The R Development Core Team 2012 ). The ‘MASS’ package (Venables and Ripley 2002 ) was required for negative binomial GLMs.

Basal cover control response

There was no significant change over time or difference between the three sites in % basal cover (arcsine transformed) for the untreated control plots ( F 3,81 = 1.54, p = 0.21).

The full model (Eq. 4 ) predicting the effects of time (DAT) and treatment groups (TG) (including their interaction) on basal cover was selected as the best model at all sites, explaining up to 70% of the variation in the data (Table 2 , Online Resource 5, Table S5.1). Basal cover decreased across all TGs, except the untreated controls at sites 1 and 3, which showed no change over time (Tables 2 , S5.2–5.4; see Table S5.5 for measured initial and final mean % basal cover values for each TG at each field trial site). There were also significant differences among TGs with some treatments reducing basal cover more than others (Fig. 3 a, Tables S5.2–5.4).

Response of F. japonica a % basal cover (R 2 = 0.61), b stem density and c light utilisation efficiency ( F v / F m , R 2 = 0.23) to 16 different treatments over time at site 3 (Taffs Well). Lines show model predicted values for the effects of each different treatment group over time. Solid black lines show values from control plots (no treatment applied). Red lines show results from the best overall performing treatment group a3 (summer and autumn foliar spray application at 2.16 kg AE ha −1 per application; 4.32 kg AE ha −1 annually). Grey lines show all other treatment groups. Dashed lines indicate 95% confidence intervals (CIs) for control and a3 treatment groups. Linear model predicted values for arcsine transformed % basal cover were back transformed for presentation in ( a ), negative binomial GLM values were used in ( b ) and untransformed linear model values used in ( c ). Coefficient estimates for all treatments are given in Supplementary Tables (Online Resource 5)

At site 1 (R 2 = 0.70), spring dig, spring picloram full rate (FR), autumn glyphosate FR foliar spray (TG d3) showed a faster decrease in cover over time than spring dig, autumn glyphosate FR foliar spray (TG d2), with both treatment groups performing significantly better than the untreated control (Table S5.2). At site 2 (R 2 = 0.27) the untreated control showed a significant increase in basal cover over time, while covering (d4) showed no significant change over time (Table S5.3).

At site 3 (TW, R 2 = 0.61), summer and autumn glyphosate half rate (HR) foliar spray (TG a3) showed a faster decrease in basal cover over time than all other treatment groups except autumn glyphosate FR foliar spray (TG a1) and autumn glyphosate stem injection (TG c1, Fig. 3 a, Table S5.4); no significant difference in basal cover decrease over time was observed between autumn glyphosate FR foliar spray (TG a1) and autumn glyphosate stem injection (TG c1).

Stem density control response

Full models examining change in stem density over time under different treatments (and their interaction) were the best models for all sites (Tables 3 , S5.6–S5.9; see Table S5.10 for measured initial and final mean stem density values for each TG at each field trial site). At site 1, spring dig, spring picloram FR, autumn glyphosate FR foliar spray (TG d3) stem density decreased faster over time than spring dig, autumn glyphosate FR foliar spray (TG d2) or the untreated control (Table S5.7). There was no change in stem density over time at site 2 under covering (TG d4) compared to the untreated control (Table S5.8).

Stem density did not change over time for the untreated control at site 3, but declined in all other treatments (Fig. 3 b, Table S5.9). Summer and autumn glyphosate HR foliar spray (TG a3) showed significantly faster declines in stem density than any of the other treatments (Fig. 3 b). Autumn glyphosate stem injection (c1) outperformed all remaining treatments except picloram-based treatments (TGs a8 and a11); however, these treatments did not perform as well as TG a3 (Table S5.9).

Light utilisation efficiency control response

Full models examining change in light utilisation efficiency over time under different treatments (and their interaction) were the best models for all sites (Tables 4 , S5.11–S5.14; see Table S5.15 for measured initial and final mean F v / F m values for each TG at each field trial site). At site 1, only spring dig, spring picloram FR, autumn glyphosate FR (TG d3) showed a significant decline in F v / F m readings over time (Table S5.12). There were no differences in the effects of different treatment groups over time on F v / F m values at site 2 (Table S5.13). At site 3, only four TGs caused a significant reduction in F v / F m readings over time: summer and autumn glyphosate HR foliar spray (TG a3), spring 2,4-D amine FR, autumn glyphosate FR (TG a4), summer glyphosate HR, autumn glyphosate HR and 2,4-D amine FR (TG a5) and spring glyphosate and 2,4-D amine HR, autumn glyphosate and 2,4-D amine HR (TG a7). Untreated control and a8 were both associated with an increase in F v / F m readings over time (Fig. 3 b, Table S5.14).

Cross-site comparisons

Given the lack of significant differences over time or sites for untreated control basal cover ( F 3,81 = 1.54, p = 0.21), we tentatively highlight the following cross-site results for preliminary comparison (Tables S5.2–S5.4). At site 2, the estimate of spring dig, spring picloram FR, autumn glyphosate FR (TG d3) was comparable to summer and autumn glyphosate HR foliar spray at site 3 (TG a3) (Fig. S5.1, Tables S5.2 and S5.4). However, while the change in basal cover under the covering treatment at site 2 (TG d4) performed significantly better than the untreated control at site 2, which saw an increase in basal coverage (Table S5.3), covering did not lead to a significant reduction in basal cover over time and therefore performed more poorly than the physiochemical treatments employed at other sites (Fig. S5.1). Given the differences in untreated control stem density and F v / F m values across the sites (Fig. S5.2), we do not make any further cross-site comparisons here.

Our study represents the largest field-based assessment of F. japonica control treatments to date, employing experimental designs at appropriate spatial and temporal scales needed for field-appropriate control of invasive, perennial, rhizome-forming species, such as F. japonica . Limited information can lead to excessive herbicide use, and costly, labour intensive and unsuccessful management strategies (Kettenring and Adams 2011 ). We show that later season (summer/stage 3 onwards, Fig. 1 ) glyphosate application provides the best control and that consideration of the above and belowground source–sink relationship increases the potential treatment window from June to October.

Through assessment of 58 treatment plots (225 m 2 ) and 348 sampling plots (4 m 2 ), this study aimed to account for extensive lateral extension of the rhizome from the aboveground stands and provide appropriate scale for the parameters measured. Sampling over 3 years following herbicide treatment ensured data was available for the recovery of vegetation, often lacking in other studies, which may overestimate the negative impact of treatments (Kettenring and Adams 2011 ). Due to difficulties in obtaining accessible field sites of sufficient scale (Kabat et al. 2006 ), previous studies have been affected by small treatment plots (Skibo 2007 ), geographically discrete, individual stands (Delbart et al. 2012 ) and split-plot designs (Child 1999 ). In our study, annual assessment of all treatment, control and sampling plots over 3 years (pre and post-treatment) delivered a robust and scale-appropriate dataset to support our conclusions.

Physical, chemical and integrated control treatment application was married with biological understanding of F. japonica . In spring (stages 1 and 2, Fig. 1 ), all control methods applied were intended to maximise resource depletion, through tillage (excavation), resource restriction (light; covering, PPO and ALS inhibitors) and/or disruption of above (synthetic auxins and ALS inhibitors) and belowground growth (picloram, synthetic auxin). Later season glyphosate application (stages 3 and 4, Fig. 1 ) aimed to maximise herbicide transit by coupling to the mass flow of photosynthates through the phloem to the rhizome (Price et al. 2002 ).

Greatest control of aboveground F. japonica growth, defined by reduced basal cover and stem density (Fig. 3 a, b), was obtained using glyphosate alone, where application timing was coupled to photosynthate flow to the rhizome (Fig. 1 ). It is notable that stem injection required 15.07 times more glyphosate per unit area than either spray treatment and was more labour intensive to apply. In plants, glyphosate (N-(phosphonomethyl)glycine) inhibits 5-enolpyruvylshikimimate-3-phosphate synthase (EPSPS) disrupting the synthesis of aromatic amino acids (e.g. tryptophan), secondary products, plant growth substances, carbon metabolism, mineral nutrition, oxidative processes and plant–microbe-interactions (Gomes et al. 2014 ). Specifically, inhibition of tryptophan synthesis in the shikimate pathway, results in suppression of indole-3-acetic acid (IAA) biosynthesis (Jiang et al. 2013 ). Upon foliar application, glyphosate penetrates rapidly through the plant cuticle prior to slow symplastic uptake. Glyphosate then moves to metabolically active sink tissues with high expression of EPSPS, i.e. F. japonica rhizome meristems (active shoot clump and rhizome buds), while aboveground tissues display limited herbicide injury. Although there is a linear relationship between glyphosate dose and tissue concentration (Feng et al. 2003 ), the distribution across leaf, stem and root tissues in F. japonica is independent of dose and is determined by sink strength (Buschmann 1997 ). This contrasts with smaller, annual dicotyledonous plants that respond in a dose-dependent manner at the whole plant level (Gomes et al. 2014 ). Mature F. japonica leaves provide a strong source of glyphosate and its relatively slow mode of action means that translocation to active rhizome sink tissues can be achieved (Cerdeira and Duke 2006 ).

Glyphosate accumulation in rhizome meristems causes extensive localised cell and tissue death via blocking of IAA biosynthesis (Gomes et al. 2014 ). Regrowth tissue showed limited chronic stress in numerous treatment plots ( F v / F m ) when compared to untreated control plants, including autumn full rate foliar spray (TG a1) (Fig. 3 c, Table S6.12) suggesting that while active meristems are poisoned effectively, regrowth occurs from healthy (previously dormant) buds of low sink strength, to which lateral rhizome translocation of herbicide is limited. Sub-lethal effects of insufficient glyphosate accumulation include aboveground tissue survival within the season of herbicide application and deformed regrowth due to retention of glyphosate in (previously) active meristems in subsequent years, due to insufficient glyphosate accumulation and/or retention (Fig. 3 ; Feng et al. 2003 ; Cerdeira and Duke 2006 ).

Significantly reduced stem density and F v / F m measurements recorded with summer and autumn glyphosate foliar spray application (TG a3) compared with autumn full rate foliar spray (TG a1, Fig. 3 b, c) suggests translocation and poisoning of active buds from June onwards (summer/stage 3) onwards, prior to mass transit of photosynthate in autumn (stage 4). Reduced TG a3 F v / F m measurements by the end of the field trials may demonstrate a chronic stress response resulting from disruption of mid-season rhizome expansion that limits its storage (source) capacity in subsequent years. Further research should aim to determine whether excess resource translocated in summer (stage 3) might support rhizome growth, while mass transit at stage 4 is used to store acquired resources to support growth in the following season. Interestingly, combining glyphosate and 2,4-D amine (TGs a4, 5 and 7) in summer and autumn also significantly reduced F v / F m measurements compared with the untreated control, yet effective control of aboveground F. japonica growth was not recorded (Fig. 3 ).

The application of synthetic auxins 2,4-D amine, picloram, aminopyralid and fluroxypyr (TGs a4 to 10, d3), ALS inhibitor flazasulfuron (TGs a11 and 12), and PPO inhibitor flumioxazine (TG a13) did not significantly reduce long-term basal cover or stem density compared with two foliar glyphosate treatments (TG a3, Fig. 3 ). This poses a potential challenge for the future management of Japanese knotweed s.l. taxa: while F. japonica is a single female clone throughout much of the invasive range, other invasive hybrid knotweeds (particularly Fallopia × bohemica ) possess greater genetic diversity (Bailey 2013 ). Consequently, reliance upon a single herbicide (glyphosate) may lead to resistance development in these hybrid populations. Accordingly, further research should be performed to find alternative effective herbicides to slow or avoid glyphosate resistance development in these species.

Integration of excavation with picloram and glyphosate (TG d3) showed a greater reduction in basal cover than without excavation (TG a8, Fig. 3 ). This was presumably through picloram suppression of active and dormant rhizome buds brought to the surface during excavation. However, TG d3 performance was comparable with summer and autumn glyphosate HR foliar spray (TG a3), despite d3’s greater labour and equipment requirements and cost. Additionally, picloram was deregulated without replacement within the EU in 2015, prohibiting use over a significant part of the invasive range. Reduction in stem density caused by pre-emergence (stage 1) and mid-season (stage 2) herbicide application allows better access to stands and has the appearance of immediate F. japonica control. However, basal cover remains high, indicating regrowth and recovery of aboveground growth without further treatment (i.e. late season glyphosate). Therefore, stage 1 and 2 treatments may not achieve sufficient resource depletion due to significant reserves held in the above and belowground F. japonica biomass.

Geomembrane covering (TG d4) was the least effective control treatment in reducing the response parameters (Online Resource 6). Integrating physical control methods with glyphosate treatments did not improve F. japonica control compared with glyphosate alone, i.e., summer cutting and autumn glyphosate application (TG d1), spring excavation and autumn glyphosate (TG d2) and autumn cut and fill (TG b1). Summer cutting has been recommended to enhance stand access (Gover 2005 ) and deplete rhizome energy reserves (Child and Wade 2000 ). However, telescopic lance spray equipment should provide access to all but the most inaccessible F. japonica stands and cutting-induced rhizome depletion has not been demonstrated empirically under field conditions. Longer-term analysis may demonstrate that excavation allows poisoning of a greater number of rhizome buds and biomass which was not detected in this 3 year study. Stem density reduction caused by autumn cut and fill treatment (TG b1) did not differ from the glyphosate spray treatments (TGs a1 and a3), despite using 20.37 times more glyphosate per unit area (87.12 kg AE ha −1 ). Cut and fill application is restricted to stems largely located around the rhizome crowns with a diameter that can accept the equipment nozzle; therefore, overall coverage of active buds with glyphosate is low. While localised poisoning of crown buds occurs, regrowth away from the crown is unaffected, indicating that lateral translocation of glyphosate is limited (Bromilow and Chamberlain 2000 ) which is compounded by the removal of the aboveground biomass that drives herbicide translocation. As such, the effect on growth is not proportional to herbicide dose—there is no evidence for a classical dose–response relationship (Streibig 2013 ).

Approximately 75% of active ingredients used as plant protection products (PPPs) in Europe before 1993 have been withdrawn from the market following the introduction of the Pesticide Authorisation Directive (PAD) 91/414/EEC in response to public concern and medical evidence demonstrating the harmful effects of pesticides on human and wildlife health (Hillocks 2012 , 2013 ). In turn, less toxic or less persistent molecules have been produced (Hillocks 2013 ) and the herbicide production industry has withdrawn support for older molecules, as sales do not support the costs involved in further (mandated) testing and re-registration. Withdrawal of certain herbicides, such as glyphosate, without suitable replacement would compromise the ability of the amenity sector to control rhizome-forming IAPs to the detriment of the wider native biodiversity and ecosystem services.

Conclusions: management of rhizome-forming IAPs

Knowledge of herbicide mode of action, appropriate dose, application timing and coverage are the most important factors for successful F. japonica control and this is relevant to other rhizome-forming IAPs such as Gunnera spp. (Gioria and Osborne 2013 ) and agricultural weed species such as Convolvulus arvensis (Tautges et al. 2016 ). Importantly, the addition of the transitional phenological source–sink stage (summer/stage 3, Fig. 1 ) may increase the logistically challenging narrow autumn treatment application timeframe and further optimisation could focus on glyphosate application and its effect on rhizome biology. Though no control treatment delivered complete eradication of F. japonica within 3 years of the first treatment application, glyphosate applied at an appropriate dose, phenological stage (Fig. 1 ) and level of coverage (using foliar spray and stem injection application) was found to be the most effective control treatment. An immediate recommendation for stakeholders is to discontinue the use of other widely used herbicides for control of F. japonica (particularly synthetic auxins) and unnecessary physical control methods (cut and fill, summer cutting and excavation) that add equipment and labour costs and increase environmental impacts, without improving control compared to spraying alone. While we recommend glyphosate use, it is acknowledged that there is a need to identify further herbicides or control approaches to reduce the potential risk of invasive hybrid knotweed populations developing resistance to the single effective herbicide. Rhizome-forming invasive species incur long-term ecological and socioeconomic costs, while few effective management tools are available, as shown by this study. Crucially, this experiment warns of further deregulation of herbicides, such as glyphosate and picloram, without equivalent replacement will lead to the application of greater quantities of ineffective herbicide products and reduce the viability and sustainability of F. japonica control.

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Acknowledgements

We are grateful to T. Rich and J. Bailey for their advice and support, particularly in the early stages of this project. We address special thanks to G. Bowes, J. Newman, A. Skibo, and A. Gover for their extensive advice and support throughout this project. We also thank S. Hathway and D. Montagnani for supplying sites and detailed site reports, respectively and C. Hipkin and B. Osborne for helpful discussions. Finally, we would like to thank the two anonymous reviewers for their suggestions and constructive comments, which helped us to improve the manuscript. This work is part-funded by the European Social Fund (ESF) through the European Union’s Convergence programme administered by the Welsh Government with Swansea University and Complete Weed Control Ltd.

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Jones, D., Bruce, G., Fowler, M.S. et al. Optimising physiochemical control of invasive Japanese knotweed. Biol Invasions 20 , 2091–2105 (2018). https://doi.org/10.1007/s10530-018-1684-5

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Research could provide new way of controlling invasive Japanese knotweed

12 Aug 2021

Japanese knotweed is pictured growing among many plants. There is a large leaf and small, white flowers with more foliage visible in the background.

Japanese knotweed. Image: Dr Mark Fennell/AECOM

Infestations of Japanese knotweed can be problematic but new research may provide a solution.

A new strategy for addressing a pesky plant has potentially been developed by researchers from NUI Galway in collaboration with infrastructure consulting firm Aecom and the University of Leeds.

Japanese knotweed is an invasive plant found in many areas of Ireland, Europe and the US, particularly in urban settings. The knotweed can reach as tall as three metres and can dominate over other plants, posing a risk to biodiversity in infested areas.

But the new research, published in PeerJ , demonstrated that fully drying out the plant in a lab made it possible to return the weed to soil without risk of regrowth. It also found that without any attached nodes, the plant’s rhizomes – which send out roots and shoots from its nodes – were incapable of regrowth.

Samples of the plant were taken from three sites in Yorkshire and Lancashire in the north of England. Two of the sites had received an application of herbicide prior to the sampling, while the third site was previously untouched.

“Japanese knotweed is one of the most invasive plant species in the world and has major negative impact on ecology and biodiversity,” said senior author of the study, Dr Karen Bacon of NUI Galway.

“The findings of this study that showed virtually no difference between the regrowth of treated and untreated Japanese knotweed samples suggest that herbicide treatment, which is often the most suitable approach to tackle the species, is not always being done effectively.”

Herbicide is a common approach to dealing with these growths but is limited by the plant’s ability to regenerate from small, surviving fragments. The plant needs unaffected rhizomes to regrow, but it was previously unclear how much material was needed for successful regeneration.

‘Our key finding, that drying out the plant effectively kills it, should provide reassurance to landowners that the plant is not as indestructible as is often stated’ – DR MARK FENNELL

The research found at least one node was necessary for successful regrowth of rhizomes and the smallest fragment weight to regenerate and survive the experiment was 0.5g. A sample this small would likely only produce a comparably small plant, which would take years to grow and spread. Nevertheless, it demonstrated the plant’s tenacity and ability to survive.

After an experiment monitoring the growth of the different plant samples, some of the fragments were left in the lab for 38 days until all of their moisture had evaporated. They were then replanted and given the same conditions as in the growth portion of the experiment.

The researchers found the plants stayed as they were with no regeneration or regrowth. Researchers said this means the strategy could prove a valuable tool in the arsenal against small and medium Japanese knotweed infestations. As well as killing the plant, it would provide a new option for dealing with the organic material, the removal of which often proves costly.

Dr Mark Fennell, associate director at AECOM and co-author of the study, said: “Our latest research sought to add to existing knowledge about how to manage and remove Japanese knotweed. Our key finding, that drying out the plant effectively kills it, should provide reassurance to landowners that the plant is not as indestructible as is often stated.

“While this invasive species remains a problem plant that can have a negative impact on biodiversity, our research provides a better understanding of the plant, paving the way for the development of more efficient and cost-effective ways of dealing with it. We hope our research helps to challenge some of the popular stigma that surrounds Japanese knotweed.”

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New Japanese knotweed standard comes into effect

As the latest RICS guidance on Japanese knotweed becomes operative, its technical author reflects on key considerations for property valuers and surveyors

Philip Santo FRICS

21 March 2022

RICS standards and guidance

Residential

Residential valuation

Japanese knotweed summer growth, showing the distinctive appearance with smooth, almost lime green spade-shaped leaves, growing alternately along a zigzag, purple-mottled stem © Philip Santo

On 23 March, the new RICS Japanese knotweed and residential property professional standard comes into effect. By complete coincidence, that date is exactly ten years since its predecessor, the information paper Japanese knotweed and residential property , was launched.

That paper introduced the first formal process for assessing Japanese knotweed risk with the so-called seven-metre rule, which has become a touchstone across the whole residential property market. Before that, there had been no agreed way of assessing the risk posed by the plant; subsequently it provided a straightforward route through to mortgage finance for most affected sales.

Standard focuses on impact not distance

Increasingly, however, experience confirmed early suspicions that seven metres was an overcautious measure of the distance that might be affected by the growth of Japanese knotweed. Also, valuers and surveyors never encountered properties where the plant had actually caused damage to substantial structures, even when growing in close proximity.

Although Japanese knotweed is undoubtedly capable of causing damage to garden walls and lightweight structures such as conservatories, this prompted the question: if it was not damaging residential buildings, what risk was the assessment process attempting to mitigate?

Eventually, academic research confirmed these reservations and reported three metres as being a more appropriate distance to use for the likely spread of an infestation beyond visible evidence. In 2019, the House of Commons Science and Technology Committee, describing the seven-metre rule as a 'blunt instrument', called on RICS and residential lenders to introduce a more nuanced and evidence-based assessment process.

The new standard directly addresses these concerns by introducing an assessment process that replaces the crude distance-based measure by reflecting the actual impact of an infestation at a property. The assessment process is still easy for valuers and surveyors to apply when Japanese knotweed is seen during site inspections, and it gives a straightforward categorisation of infestations.

This retains simplicity – which is essential for the residential property market – so the actions needed to make an affected property mortgageable will still be clear to all parties. The guidance has stimulated great interest since its publication, including in the media , and to date has had more than 2,000 unique downloads from the RICS website.

'The assessment process is still easy for valuers and surveyors to apply when Japanese knotweed is seen during site inspections'

Categories created for response

So what does the guidance mean for the residential practitioner? Whenever Japanese knotweed is seen within the boundaries of a property, it should be categorised at one of three levels.

Management Category A: Action means that Japanese knotweed is present and is causing visible material damage to a significant structure. This is likely to affect value because repair and remediation costs will be incurred.

Management Category B: Action means there is no material damage to structures, but that Japanese knotweed is likely to prevent use of or restrict access to amenity space. This may still affect value, but that will be related more directly to the cost of remediation because no structural repairs will be needed.

Management Category C: Manage means that Japanese knotweed is present, but it is not causing damage or affecting amenity. Consequently, the impact on value will be much lower because the structures and amenity of the property have not been adversely affected, and any remediation costs will be at the discretion of the owner.

When an assessment is Management Category A or B, most lenders are expected to impose retentions on mortgage advances pending receipt of a remediation specialist's report – hence the word 'Action' in the category title. By contrast, when the assessment is Management Category C: Manage, the expectation is that no retention will be imposed because the infestation has not directly affected structures or amenity at the property.

When infestations are seen off site, the previous assessment process required categorisation if they were within seven metres of the boundary. Responding to the latest research, this distance has now been reduced to three metres and falls under Management Category D: Report .

Lenders are not expected to make a mortgage retention for such cases because the property owner or mortgage applicant has no control over adjoining land. Infestations more than three metres beyond the boundary are not categorised or reported to lenders, although a record should be made in site notes.

The requirements of property owners are obviously different from those of lenders and, when reporting to clients for purposes other than lending, surveyors and valuers will still use one of the same four categories whenever Japanese knotweed is seen.

In all cases, however, there will be a recommendation for the client to obtain advice from a remediation specialist. When an infestation is seen more than three metres beyond the boundary, the detail of any reporting will depend on the type of inspection and report being provided, and the nature of the infestation.

Advice on specific remedial action is not required. As with many other potentially significant issues affecting property value or ownership, the objective for the surveyor or valuer is to identify and report the matter to the client, but then for an appropriate specialist to provide advice on what action to take. In this, there are clear parallels with problems such as dry rot, defective services or structural failure.

Again, as is the case for other property defects, the guidance acknowledges that there are many legitimate reasons why an infestation of Japanese knotweed might not be seen during a competently conducted inspection. Nevertheless, if Japanese knotweed is clearly visible on site during the normal course of an inspection then it is reasonable to expect, all other things being equal, that it should be identified and reported to the client.

There were initially some queries about whether these changes might increase potential liabilities. However, the guidance clarifies that the requirements for inspections are no greater than – but likewise no less than – those outlined in the RICS Valuation – Global Standards 2017: UK national supplement , UK VPGA 11 Valuation for residential mortgage purposes, or in RICS' Home survey standard for private surveys.

In particular, the guidance stresses that the change in the assessment process to a three-metre distance beyond a boundary does not imply any greater inspection requirement than under the previous seven-metre distance.

Recognising that its readership will be far wider than RICS members, the guidance explains the difference between mortgage valuations and surveys, and points out that valuations and pre-purchase surveys by members should not be regarded as equivalent to, or substitutes for, an inspection by a specialist remediation company.

PCA offers supporting guidance

In addition to this RICS professional standard, residential practitioners are strongly advised to download the parallel publication by the Property Care Association (PCA): Japanese knotweed – Guidance for professional valuers and surveyors . The PCA guidance is specifically designed to support the new RICS standard and gives property valuers and surveyors advice on all aspects of knotweed surveys, including identification, indicative costing for remedial treatment and remediation options.

Philip Santo FRICS is director of Philip Santo & Co and technical author of the professional standard Contact Philip: Email | LinkedIn

Related competencies include : Inspection, Valuation, Valuation reporting and research

The RICS Member CPD Support Pack includes access to a free webinar on the new guidance – log in to the RICS online academy to access further information

Japanese knotweed and residential property guidance note

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Japanese knotweed ( Fallopia japonica ): an analysis of capacity to cause structural damage (compared to other plants) and typical rhizome extension

Mark fennell.

1 AECOM, Cambridge, UK

Karen L. Bacon

2 School of Geography, University of Leeds, Leeds, UK

Associated Data

The following information was supplied regarding data availability:

The raw data are provided in the Supplemental Files .

Fallopia japonica (Japanese knotweed) is a well-known invasive alien species in the UK and elsewhere in Europe and North America. The plant is known to have a negative impact on local biodiversity, flood risk and ecosystem services; but in the UK it is also considered to pose a significant risk to the structural integrity of buildings that are within seven m of the above ground portions of the plant. This has led to the presence of the plant on residential properties regularly being used to refuse mortgage applications. Despite the significant socioeconomic impacts of such automatic mortgage option restriction, little research has been conducted to investigate this issue. The ‘seven-m rule’ is derived from widely adopted government guidance in the UK. This study considered if there is evidence to support this phenomenon in the literature, reports the findings of a survey of invasive species control contractors and property surveyors to determine if field observations support these assertions, and reports a case study of 68 properties, located on three streets in northern England where F. japonica was recorded. Additionally, given the importance of proximity, the seven-m rule is also tested based on data collected during the excavation based removal of F. japonica from 81 sites. No support was found to suggest that F. japonica causes significant damage to built structures, even when it is growing in close proximity to them and certainly no more damage than other plant species that are not subject to such stringent lending policies. It was found that the seven-m rule is not a statistically robust tool for estimating likely rhizome extension. F. japonica rhizome rarely extends more than four m from above ground plants and is typically found within two m for small stands and 2.5 m for large stands. Based on these findings, the practice of automatically restricting mortgage options for home buyers when F. japonica is present, is not commensurate with the risk.

Introduction

Japanese knotweed ( Fallopia japonica ) is a tall, herbaceous, perennial plant with woody rhizomes when mature. F. japonica is now recognised as one of the most problematic weeds in the UK and Ireland ( Environment Agency, 2013 ; Property Care Association (PCA), 2018 ). It is also recognised as one of the worst invasive alien species (IAS) at a European scale ( Nentwig et al., 2017 ) and globally ( Lowe et al., 2000 ), being particularly invasive in parts of North America, Europe, Australia and New Zealand ( Centre for Agriculture and Bioscience International (CABI), 2018a ). On a global scale its reputation as a problematic IAS primarily stems from its vigorous growth and impacts on riparian habitats ( Child & Wade, 2000 ) coupled with difficulty of eradication ( Bailey, 2013 ; Jones et al., 2018 ). Verified impacts include the creation of dense monodominant stands ( Gillies, Clements & Grenz, 2016 ; Michigan Department of Natural Resources (MDNR), 2012 ); reductions in ecosystem services in riparian zones, for example by impeding access ( Environment Agency, 2013 ; Gerber et al., 2008 ; Kidd, 2000 ; Urgenson, 2006 ); negative effects on native plant and invertebrate assemblages in riparian habitats ( Gerber et al., 2008 ); reductions in species richness ( Aguilera et al., 2010 ; Hejda, Pyšek & Jarošík, 2009 ; Urgenson, 2006 ) and abundance of native understory herbs, shrubs and juvenile trees in riparian woodlands ( Urgenson, 2006 ); modifications to nutrient cycles ( Urgenson, 2006 ); and impacts on flood defence through impeding water flow and facilitation of riverbank erosion ( Booy, Wade & Roy, 2015 ; Environment Agency, 2013 ; Kidd, 2000 ).

The plant is associated with significant economic impacts in the UK, particularly in the development sector, due in large part to soil containing the species being classified as controlled waste, which can result in significant waste management costs ( Williams et al., 2010 ; Pearce, 2015 ). Economic impacts have been estimated at £166,000,000 per year ( Williams et al., 2010 ) in the UK; however, the validity of this, frequently misquoted, figure is strongly debated ( Pearce, 2015 ).

Fallopia japonica was introduced to Europe from Japan in the mid-19th century by the Bavarian Phillip von Siebold, a renowned importer of exotic plants at this time ( Bailey, 2013 ). In 1850, von Siebold sent a package to Kew Gardens in London, which included a female (male sterile) F. japonica plant ( Bailey, 2013 ). Once established in Kew Gardens it was distributed throughout the UK, being planted in Victorian parks and gardens ( Bailey, 2013 ). Despite rumblings from Victorian gardeners as far back as 1898, for example William Robinson ( Bailey & Conolly, 2000 ), about the plant’s invasiveness, it was available for sale in UK nurseries up until at least 1990 ( Philip, 1990 ). It was first recorded outside cultivation in South Wales in 1886 ( Storrie, 1886 ) and is currently recorded in most hectads within the UK and Ireland ( Botanical Society of Britain and Ireland (BSBI), 2018 ; Fig. 1A ).

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(A) Records from the Botanical Society of Britain and Ireland live database based on presence/absence data in each hectad. Almost all hectads report fewer than 100 records. Map was produced using records collected mainly by members of the Botanical Society of Britain and Ireland (BSBI) (2018) . (B) British Geological Society map showing areas at risk of shrink-swell action. Reproduced with the permission of the British Geological Survey © UKRI. All rights reserved ( British Geological Survey (BGS), 2018 ).

By the late 1970s, the invasive nature of F. japonica was becoming widely recognised ( Bailey, 2013 ) in the UK (also see ‘Study species: Fallopia japonica ’ below). Within the popular press and through various online sources, F. japonica is increasingly sensationalised and is credited on a regular basis with an ability to ‘grow through concrete’ and ‘destroy building foundations’ ( Ellery, 2016 ; Sweeny, 2017 ; Willey, 2018 ). Accordingly, in the 21st century, property surveyors and lenders started taking an increasingly risk-averse approach to the species ( Royal Institution of Chartered Surveyors (RICS), 2012 ). Ultimately, this has led to the presence of F. japonica on or near a residential property preventing its sale ( Royal Institution of Chartered Surveyors (RICS), 2012 ; Pearce, 2015 ). Frequently, financial institutions will automatically restrict mortgage options where F. japonica is within the boundary of the property or within seven m of a habitable space, conservatory or garage. This ‘seven-m rule’ is derived from widely adopted government guidance, which states that F. japonica rhizome may extend seven m laterally from a parent plant ( Environment Agency, 2013 ).

Where F. japonica is preventing a property sale, this issue can typically be resolved if evidence can be provided to a lender that an appropriate treatment programme, effective against F. japonica , is in place ( Royal Institution of Chartered Surveyors (RICS), 2012 ). Such control programmes can be expensive; between £2,000 and £5,000 in total for a typical three-bedroom semi-detached house (at December 2011; Royal Institution of Chartered Surveyors (RICS), 2012 ). Additionally, the stigma associated with the species can result in diminution of property value ( Santo, 2017 ) even following control action. The cumulative impact of the above is that home owners can lose all, or a significant portion, of their property’s value. This automatic restriction of mortgage options where F. japonica is present on or near a property has led to significant hardship and associated, often reported, emotional stress ( Dunn, 2015 ; The Telegraph, 2015 ). The claimed ability of F. japonica to cause significant structural damage is widely acknowledged within the professional weed control sector in the UK as not being representative of the vast majority of casual field observations and that, due to current public perception, impacts on the market value of a property are out of proportion to the cost of remediation ( Santo, 2017 ).

In order to understand if the lender response to F. japonica presence, described above, is proportionate, the impacts typically associated with F. japonica must be compared to those of other plants. The potential for plants, in general, to cause issues in the built environment is well understood. Accordingly, in the UK, developers follow guidance ( NHBC, 2017 ) when building near trees. The automatic restriction, however, of mortgage options due to the mere presence of a plant species is a new phenomenon. Although this is currently a UK phenomenon, recent reports have emerged of F. japonica presence impacting property sales in the Republic of Ireland (C. O’Flynn, 2018, personal correspondence), suggesting that this issue has the potential to spread, and sensationalist articles have begun to appear in North American tabloids ( The Calgary Eyeopener, 2015 ).

Plants are known to cause damage to built structures primarily by three mechanisms: (i) indirect damage, via subsidence or heave, caused by plant-mediated modifications to soil water content ( Biddle, 2001 ; O’Callaghan & Kelly, 2005 ), (ii) direct damage due to physical impact, typically associated with falling trees ( O’Callaghan & Kelly, 2005 ) and (iii) direct damage caused by physical pressure exerted through growth ( Biddle, 1998 , 2001 ).

There are many causes of subsidence, with plants only contributing to a proportion of the total and only then on shrinkable clay soils. Plant-mediated subsidence in such soils occurs when plants remove water from the soil through a process called transpiration and, as a result of this removal of water, the soil shrinks. This is particularly common during the summer months and/or periods of drought. The soil swells again once water is returned via rainfall. If foundations are not sufficiently deep or strong to withstand such stress, this process can lead to structural damage over time, typically characterised by vertical cracks up through the brickwork. Swelling of soil can also occur when mature trees, that were helping regulate soil moisture content, are removed ( NHBC, 2017 ).

While the mechanisms behind impact-based direct damage are relatively straight forward, a range of factors—biological, chemical and physical—become relevant with respect to direct damage caused by physical pressure. Plants acquire the energy they need to grow through photosynthesis, which converts light energy, carbon dioxide and water into chemical energy that can later be released to fuel the plant’s activities. Driven by the energy produced by photosynthesis, plant roots and rhizomes grow through the soil seeking water and nutrients. Ultimately, using the products of both photosynthesis and the materials collected by roots/rhizomes, plants grow (increase in biomass) and reproduce. These growing underground plant structures follow the path of least resistance through the soil along water and/or chemical gradients, typically from areas of low water or nutrient concentration to areas of higher water or nutrient concentration ( Rellán-Álvarez, Lobet & Dinneny, 2016 ). When solid structures (natural or anthropogenic) are encountered by extending plant tissue, highly sensitive receptors on the outer surface on the plant detect the change in pressure, resulting in the release of plant growth regulators and chemical signals that stimulate differential growth rates within plant tissues, ultimately causing the plant to grow away from the solid structure and find the path of least resistance ( Takeda et al., 2008 ) where possible. However, where a plant becomes trapped between two structures and growth away from or around the structure is no longer possible, the risk of damage increases. The greatest risk of direct damage occurs close to the main trunk, stem or crown; this is due to incremental growth of such structures over time and secondary thickening of the roots/rhizomes, which are thickest in close proximity to such structures.

The impacts of F. japonica on residential property sale and value are ultimately predicated on the species’ ability to cause significant structural damage, but this proposition has never been scientifically tested. This paper, therefore, proposes a methodology for conducting such assessments and implements the proposed methodology using a case study of 68 residential properties in the north of England, with the aim of determining the capacity of F. japonica to cause structural damage relative to other common plants in the UK. The paper also includes an assessment of published records of F. japonica ’s ability to cause structural damage; an assessment of how plants cause structural damage in the context of F. japonica ’s biology; and an assessment of the findings of two surveys conducted on members of the Royal Institution of Chartered Surveyors (RICS) and the Property Care Association’s (PCA) Invasive Weed Control Group (IWCG). Additionally, given the importance of proximity, the seven-m rule is tested, based on an assessment of a survey carried out on members of the PCA’s IWCG, with the aim of determining typical rhizome extension distance relative to above ground F. japonica plants.

Materials and Methods

Study species: fallopia japonica.

Fallopia japonica is a tall, vigorous, clump-forming, herbaceous perennial, which grows up to two to three m in height ( Fig. 2A ) and often forms dense thickets. The stems are robust, bamboo-like, slightly fleshy and hollow, with a diameter of up to four cm. Tall-brown to bronze canes remain over winter and persist for approximately 3 years. Leaves are 10–15 cm long, lush, light green and shield-shaped with a flattened base ( Fig. 2B ). Growth over successive years builds up a sturdy dense crown at the base of canes ( Fig. 2C ). New growth primarily emerges from crowns at the start of the growth season, but also directly from rhizomes. Rhizomes are initially white, extremely fleshy and fragile while extending ( Fig. 2D ), but mature into yellow/orange sturdier woody structures ( Fig. 2D ). The majority of rhizome is found in the upper 50 cm of soil, but it can penetrate down to three m and, depending on soil type and site features, spread up to 10 m from parent plants is possible under very rare circumstances ( Booy, Wade & Roy, 2015 ). Only female (male sterile) plants are known to be present in the UK, which form drooping grape-like clusters of flowers with distinct stigmas. Seeds are shiny, triangular, dark brown, three to four-mm long, two-mm wide and sterile in the UK. See Booy, Wade & Roy (2015) for additional information on the biology of the species. F. japonica can regenerate from rhizome fragments weighing as little as 0.7 g ( Brock & Wade, 1992 ), providing a node is present, and from stem sections, where suitable conditions are present (very moist, well-lit soils with high nutrient availability). The species is dispersed effectively in transported soil and by water ( Environment Agency, 2013 ; Booy, Wade & Roy, 2015 ). F. japonica is tolerant of a wide range of habitat and soil types, but is most frequently found in disturbed urban habitats, particularly brownfield sites, railway verges and the banks of waterways, where it thrives in damp soils.

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(A) F. Japonica growing within the case study area. (B) Specimen of F. japonica leaves, stem and inflorescence. (C) F. Japonica crown, associated with the plant from panel A. (D) Specimen of F. japonica mature rhizome with immature rhizomes emerging. Photos by M. Fennell.

Fallopia japonica is closely related to two other members of the Fallopia genus, F. sachalinensis and Fallopia x bohemica , which have similar invasive ranges and have similar impacts. Of note, in some parts of its invasive range, Fallopia x bohemica spreads via the production of large numbers of wind-dispersed viable seeds that germinate at rates approaching 100% in some populations ( Gillies, Clements & Grenz, 2016 ). However, spread by this means does not currently occur in the UK.

Literature assessment

In order to contextualise impacts associated with F. japonica within the larger subject of the capacity of plants that cause structural damage, this study assessed various guidance documents and papers published on the topic of plants causing damage and the relationship between various plant traits and capacity to cause damage. The primary points of interest from these documents are highlighted in ‘Plants and structural damage’. Additionally, a focused literature search on Web of Science was conducted on 27th June 2017 to identify academic papers that provide reference to or evidence of F. japonica -mediated damage to structures. The search terms used for the Web of Science search were ‘ F. japonica ’ and ‘ Polygonum cuspidatum ’, an old name for the same species, and within the returned publications ‘damage’. The abstracts were reviewed to determine what type of damage was referred to within the paper.

Fallopia japonica impact survey

A survey of F. japonica management contractors (PCA) and property surveyors (RICS) was conducted to collect evidence either for or against the assertion that F. japonica is a major cause of structural damage to properties. Survey forms were sent out to contractors and surveyors to determine, based on their last field observation of F. japonica , the presence, if any, of damage linked to the presence of the plant across a range of built structure types (see Table 1 for included questions; see Supplemental Information S1 for individual responses). In total, 51 PCA members and 71 RICS surveyors provided records relating to 122 properties ( Table 1 ). Each respondent was also asked how far the closest evident aboveground F. japonica plant was from the residential building on the site that they had visited. This was cross-referenced against reports of damage ( Table 2 ). Yes/No responses are presented as raw numbers and converted to percentage values and differences between PCA and RICS respondents were considered. Statistical analyses were undertaken in PAST version 3.15 ( Hammer, Harper & Ryan, 2001 ).

Question	Contractor responses ( = 51)		Surveyor responses ( = 71)
Question	Yes	No	Yes	No
Q1: Was there evidence of defects or structural damage to the residential building caused by the Japanese knotweed?	2% (1)	98% (50)	6% (4)	94% (67)
Q2: Was there evidence of defects or structural damage to retaining garden walls, sheds, garages, greenhouses or lightly built garden structures caused by the Japanese knotweed?	35% (18)	65% (33)	23% (16)	77% (55)
Q3: Was there evidence of defects or structural damage to drains, sewers and other subterranean services caused by the Japanese knotweed?	16% (8)	64% (43)	3% (2)	97% (66)
Q4: Was there evidence of loss of amenity to the garden or grounds resulting from the presence of Japanese knotweed?	51% (26)	49% (21)	18% (13)	82% (55)

Results are presented as percentages for easier comparison between contractor and surveyor respondents and rounded to the nearest whole number. The actual number of responses are included in brackets. n = sample size. Three surveyors did not answer the third and fourth questions making n = 68 for those responses (see Supplemental Information S1 for more details).

Distance from residential property in m	Number reported by contractors ( = 46). Reports of damage in brackets	Number reported by surveyors ( = 65). Reports of damage in brackets
0–1.0	10 (1)	9 (3)
1.1–2	8 (0)	3 (0)
2.1–3	4 (0)	7 (0)
3.1–4	2 (0)	6 (1)
4.1–5	3 (0)	5 (0)
5.1–6	3 (0)	1 (0)
6.1–7	3 (0)	4 (0)
7.1–8	2 (0)	3 (0)
8.1–9	2 (0)	1 (0)
9.1–10	2 (0)	8 (0)
10.1–11	No record	1 (0)
11.1–20	4 (0)	9 (0)
20.1–30	2 (0)	4 (0)
30.1–40	No record	No record
40.1–50	No record	3 (0)
50.1 or greater	1 (0)	1 (0)

Fallopia japonica rhizome extent survey

The survey of PCA contractors also asked respondents to provide details, based on the last five F. japonica excavation-based remediation works that they had conducted, on the above ground area of F. japonica and to provide the horizontal (i.e. distance from visible above ground plants) and vertical (i.e. distance from soil surface) extent of rhizomes encountered. In total, 26 contractors provided records of 81 excavations with sufficient detail (e.g. clear rhizome extent linked to an identified individual stand) to be included in the assessment. Eight records were removed due to reporting multiple stands, partial excavation or disturbed sites where it was not possible to accurately determine the rhizome extent from an individual stand (see Supplemental Information S1 ). Subsequently, stands were sub-classified into either ‘small’ or ‘large’ categories. The small category included any plants that covered a soil area of four m 2 or less, aimed at encompassing the typical size of stands found in small residential gardens. Stands covering an area greater than this were placed into the large category. This allowed for an examination of the relationship between above-ground area and rhizome extension, as well as an analysis of typical rhizome extension. Data were tested for normality (Anderson–Darling test) and differences between stand categories (large or small) were tested using the Mann–Whitney U test for non-normally distributed data. Data analyses were conducted using PAST version 3.15 ( Hammer, Harper & Ryan, 2001 ).

A survey was conducted on 68 residential properties located on three streets in northern England. The houses on all three streets were built prior to 1900 ( Consumer Data Research Centre (CDRC), 2018 ). All properties have been abandoned for at least 10 years and were in a state of disrepair, with most having cracked patios and crumbling brickwork (particularly on boundary walls). F. japonica was previously known to be present on properties located on all three streets. An assessment was carried out in September 2017 to determine any constraints that the species might pose to restoration and re-development (see Supplementary Information S2 for details). These sites represented a close to ‘worst case’ scenario in terms of susceptibility to damage from unchecked plant growth. With this in mind, a survey was conducted to determine presence and associated damage for F. japonica , trees, woody shrubs and woody climbers. All damage was compared against a baseline of existing damage that was present due to neglect, weathering and wear and tear over the lifetime of the properties, regardless of plant presence. Where plants were associated with damage to a structure, the damage was quantified based on the scale presented in Table 3 (see also Supplemental Information S2 ). Figure 3 presents examples of the rating scale that was applied.

Rating	Rating description
0	Not associated with damage (e.g. just growing in soil or present beneath the soil)
1	Correlation with existing damage (e.g. emerging from a crack in paving or a gap in brickwork, but with no detectable variation away from baseline damage)
2	Minor exacerbation of existing damage (e.g. a detectable increase in crack width away from baseline damage)
3	Moderate exacerbation of existing damage (e.g. a detectable addition to damage away from baseline damage, i.e. new cracks forming around an initial crack)
4	Major exacerbation (damage beyond cracking, e.g. a damaged wall becoming undermined)
5	Causing minor damage (e.g. creating a crack)
6	Causing medium damage (e.g. creating a crack which has spread to form additional cracks)
7	Causing major damage (damage beyond cracking, e.g. a previous undamaged wall becoming undermined, or concrete hard standing being significantly lifted and cracked, or a roof being smashed in due to collapse)

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(A) Example of non-plant-based wear and tear to hard standing. (B) Rating ‘0’— B. davidii growing in a raised landscaping area, having no discernible impact on undamaged adjacent built structures. (C) Rating ‘1’— F. japonica emerging from existing cracks in paving at the base of a wall, causing no discernible impact away from baseline damage. (D) Rating ‘2’— F. japonica emerging from existing gaps in worn paving, while the gap has not been widened some mortar has been pushed aside. (E) Rating ‘3’— B. davidii growing out of a crack in worn concrete hardstanding, with additional cracks forming in the area. F. japonica visible in the background emerging from similar cracks in the hardstanding, also exacerbating existing damage but to a lesser extent. (F) Rating ‘3’— B. davidii growing out of cracks in worn brickwork, with additional cracks forming in the area. (G) Rating ‘4’— B. davidii growing out of cracks in worn brickwork. It has found its way between two structures and is facilitating the dilapidation of the wall and pushing out brickwork. (H) Rating ‘6’— B. davidii growing behind a small retaining wall and pushing some brickwork over. (I) The remains of a tree stump, which have destabilised the base of what remains of a dilapidated wall. Photos by M. Fennell.

By chance, a large number of Buddleja davidii (buddleia) plants were present at the case study sites. As such, this species was included in the assessment separately from other woody plants. B. davidii is a non-native woody shrub that is known to be invasive in the UK and elsewhere ( Centre for Agriculture and Bioscience International (CABI), 2018b ). Damage associated with the following species or plant groups are discussed in this case study: F. japonica , B. davidii , ‘trees’ (other woody, independently standing mature plants) and ‘woody climbers’ (woody plants that are not independently standing, e.g. attached to walls). In addition to presence, for F. japonica , mature (with crowns) and immature (without crowns) plants were assessed. Similarly, for B. davidii , mature (woody) and immature (not woody) plants were considered.

Plants and structural damage

The literature assessment revealed that indirect damage, typically characterised by subsidence caused by modifications to soil moisture content, was by far the most relevant mechanism identified by which plants caused major damage to built structures ( Biddle, 2001 ; O’Callaghan & Kelly, 2005 ) and high water-use tree species were the most likely plant type to cause this type of damage ( NHBC, 2017 ).

Such impacts are only a potential problem on shrinkable clay soils ( Biddle, 2001 ; O’Callaghan & Kelly, 2005 ). Clay soils are found in less than 50% of the UK and not all clay soils will be equally shrinkable. The degree to which a clay soil is shrinkable depends on its mineral composition. All clay minerals are built from combinations of two types of molecular sheet, (i) a sheet with repeating units of silicon surrounded by four oxygen atoms in a tetrahedron and (ii) a sheet with an aluminium or magnesium atom surrounded by six oxygen or six hydroxyl molecules in an octahedron. How these sheets are arranged determines how ridged the clay soil is. For example, soils composed of alternating sheets, one tetrahedron followed by one octahedron, and so on, and held together by a pair of hydrogen ions are quite ridged. However, when an aluminium octahedral sheet is between two silicon tetrahedral sheets and held together by weak oxygen bonds a clay called montmorillonite is formed, which is a relatively weak clay susceptible to shrinkage ( Chapman, 2012 ). Surveys by the Botanical Society of Britain and Ireland ( Fig. 1A ) show that F. japonica has been found in most areas of Britain but only a small fraction of this area is identified by the British Geological Society as having moderate to high risk of swell-shrinkage ( Fig. 1B ), with most shrinkable clays being found in the south east of England. Additionally, it is likely that the area at actual risk of plant-mediated shrinkage is lower again because not all of this area necessarily has the correct mineral combination required to be at high risk for facilitation of subsidence.

The second most relevant mechanism by which plants cause damage, was identified as direct damage due to physical impact, typically characterised by trees falling and striking buildings and power lines ( O’Callaghan & Kelly, 2005 ) and is only relevant to large plants such as trees.

Finally, plants can also cause direct damage to buildings and structures by pressure exerted through growth; however, this is comparatively rare in terms of meaningful damage; it is also well understood ( Biddle, 1998 , 2001 ). While growth at the base of plants, or of roots near the surface, exerts relatively small forces, paving slabs or low boundary walls can be lifted or pushed aside. Heavy loaded or stronger structures are more likely to withstand these forces without damage, as plants preferentially distort around such obstruction before damage occurs ( British Standard, 2012 ). Certain combinations of variables can increase the potential for damage, for example water leaking from damaged drains, sewers or water mains can encourage localised root growth, as plants typically grow towards areas of higher water availability, which can lead to roots/rhizomes entering a drain or sewer through the defect and proliferating, causing blockage and an enlarging of the initial defect. The risks associated with direct pressure based damage are (i) primarily associated with trees, (ii) vary for different types of structures and (iii) diminish rapidly with distance. Minimum recommended planting distances for young trees or new planting, to avoid direct damage to a structure from future tree growth, are described in British Standard (2012) and range from (i) no minimum distance required for planting trees near buildings, heavily loaded structures, services greater than one m deep, and masonry boundary walls, where the tree will have a stem diameter below 0.3 m (at 1.5 m above ground level) at maturity to (ii) three-m distance required for planting trees near paths and drives with flexible surfaces, paving slabs, and services less than one m deep, where the tree will have a stem diameter above 0.6 m (at 1.5 m above ground level) at maturity ( British Standard, 2012 ).

These three mechanisms described above are evaluated against the biology and growth characteristics of F. japonica in ‘Indirect damage: in the context of F. japonica ’ and ‘Direct damage: in the context of F. japonica ’.

Based on the literature assessment, there is essentially no evidence to support the claim that F. japonica causes damage in excess of the norm for many plants. While evidence was found to support the claim that trees can cause major damage, no such evidence could be found for F. japonica . Of particular interest were records of insurance claims related to trees being involved in subsidence issues: 12,800 such records, between 2002 and 2005, were identified by Mercer, Reeves & O’Callaghan (2011) , 1,030 of which met their criteria for records having sufficient detail to assess and as being important from a subsidence risk perspective. The top five genera implicated in subsidence-related insurance claims were Oak ( Quercus ), Ash ( Fraxinus ), Cyprus ( Cupressus ), Maple ( Acer ), and Willow ( Salix ). At maturity, these trees frequently reach 24, 23, 20, 18 and 24 m, respectively. No evidence of any insurance claims was identified for F. japonica with respect to structural damage. While many recent papers include in their description of F. japonica that the species can cause notable damage to built structures ( Mclean, 2010 ; Djeddour & Shaw, 2010 ), this claim is never supported by evidence.

Based on the search terms ‘ F. japonica ’ and ‘ P. cuspidatum ’, the Web of Science search returned 778 journal papers published between 1937 and 2016. When the term ‘damage’ is included the number of papers dropped to 46. Five were removed for being irrelevant. Of the remaining 41 papers, 15 focused on biocontrol, 20 on general biology/genetics, two on ecological damage and two on other interactions. None of the abstracts suggested that the papers would focus on structural damage but some did refer to it as a ‘known problem’. This highlights the limited academic engagement with the problem—it appears to be accepted without supporting evidence that F. japonica causes clear and problematic structural damage.

Survey results

Survey results (reported damage).

In total, 51 contractors and 71 surveyors responded to the survey. Details of the responses are provided in Tables 1 and and2. 2 . The results of the two property damage surveys (PCA and RICS) showed clearly that reports for defects or structural damage to residential properties, where F. japonica is present, were extremely rare (between 2% and 6%). As the survey data are interpreted as a worst case situation, it is likely that more detailed surveys would reduce this number, if specifically designed to discriminate between causation, exacerbation and correlation. This statement is relevant to all types of damage reported. Reports of damage to lighter structures such as sheds or paths were more apparent, with 35% (PCA) and 23% (RICS) of respondents noticing such damage. Reports of damage to drains or subterranean services were low, 16% (PCA) and 3% (RICS). The only question to obtain a ‘yes’ above 50% was for Question 4 from the PCA contractor surveys where 51% noticed evidence for loss of amenity. However, only 18% of surveyors considered that the F. japonica observed was likely to impact garden amenity ( Table 1 ). There was also a clear difference between the responses of surveyors and contractors for Question 3 ( Table 1 ), with contractors reporting more damage than surveyors. It should be noted that PCA contractor members are more likely to be called out where problematic stands of F. japonica are present, which could account for the differences observed between groups. It could also be explained by differences between the two groups with respect to training, perception or bias. Investigating this was beyond the scope of the current study.

Each respondent was also asked how far the closest evident aboveground F. japonica plant was from the residential building on the site that they had visited ( Table 2 ). This was cross-referenced ( Table 2 ) against reports of damage, as per Question 1 ( Table 1 ). One contractor (PCA) reported damage caused by F. japonica ( Table 1 ); in this case the closest reported plant to the property was one m ( Table 2 ). Four surveyors (RICS) reported damage caused by F. japonica ( Table 1 ). Two stated that the nearest plants were zero m from the property, one stated one m from the property and one stated four m from the property ( Table 2 ). It is worth noting that the report at four m was for a property built prior to 1900. No other responses suggested that F. japonica had caused damage to the residential property. Among contractors reporting no damage to the residential property, 25 reported F. japonica growing within four m of the residential property and a further nine reported F. japonica growing within seven m of the residential property. Among surveyors, 21 reported F. japonica within four m of the residential property and a further ten reported F. japonica within seven m of the residential property and none of these reports were linked to damage to the property. See Table 2 for more detail.

Survey results (reported rhizome extension)

There was a statistically significant difference (Mann–Whitney U ; p < 0.05) in the horizontal extent of F. japonica rhizomes between small and large stands, with larger stands found to have further reaching rhizomes ( Fig. 4 ). None of the small stands included in the assessment had rhizomes extending further than four m, and the majority (75%) had rhizomes extending two m or less. The average rhizome extension reported for small stands was 1.4 m. Only one plant in the large category had rhizome extension greater than five m (identified as a statistical outlier); all other records were below four m and the majority (75%) had rhizome extensions of 2.5 m or less.

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The box represents the lower 25 percentile, the median value and the upper 25% percentile and the whiskers represent the range of the data. The circle represents an outlier value (greater than two standard deviations away from the median value). Mann–Whitney U : U = 412; p < 0.05 ( p = 0.01802). N = 21 (small) and 60 (large).

There was also a statistically significant difference (Mann–Whitney U ; p < 0.001) between the large and small stands for vertical rhizome extent, with larger stands found to have deeper reaching rhizomes ( Fig. 5 ). No records with vertical rhizome extent in excess of 3.5 m were recorded. The small stands had rhizomes with a mean 1.02 m depth and a maximum of two m, whereas the maximum vertical extent recorded for the large stands was 3.2 m and the mean was 1.64 m.

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The box represents the lower 25 percentile, the median value and the upper 25% percentile and the whiskers represent the range of the data. The circle represents an outlier value (greater than two standard deviations away from the median value). Mann–Whitney U : U = 260; p < 0.0001 ( p = 6.105 e− 5 ). N = 21 (small) and 60 (large).

In all but the most severe examples, the level of damage caused by plants did not exceed damage that was observed elsewhere within the study area in locations where plants were not growing. It would appear, in the context of dilapidation, that plants are generally not the cause but rather an accelerator to natural weathering and dilapidation.

Fallopia japonica was identified within the boundary of six properties (five mature stands and one immature stand) and the plant was identified within seven m of the main building of a further 12 properties, leading to a total of 18 properties where F. japonica was within the area identified by the ‘seven-m rule’ as being at risk. B. davidii was identified on 62 properties (31 mature and 31 immature). Trees were observed on six properties and woody climbers were observed on four.

In general, F. japonica was linked to less damage than the other species/species groups assessed ( Table 4 ). Where F. japonica was linked to damage, mature plants were more likely to exacerbate the damage than to have been the original cause. There were no reported incidences of immature F. japonica causing or exacerbating damage.

	Plant damage to house			Plant damage to walls			Plant damage to paving
	Plants linked to damage, % of occurrences	Plants linked to damage, % of total properties	Average damage score	Plants linked to damage, % of occurrences	Plants linked to damage, % of total properties	Average damage score	Plants linked to damage, % of occurrences	Plants linked to damage, % of total properties	Average damage score
	0% 0/18	0% 0/68	0	11% 2/18	3% 2/68	0.029	33% 6/18	9% 6/68	0.176
	68% 42/62	62% 42/68	0.75	79% 49/62	72% 49.68	1.529	73% 45/62	66% 45/68	0.824
Trees	33% 2/6	3% 2/68	0.132	67% 4/6	6% 4/68	0.235	50% 3/6	4% 3/68	0.176
Woody climbers	75% 3/4	4% 3/68	0.103	75% 3/4	4% 3/68	0.044	0% 0/4	0% 0/68	0

Average damage score = the average damage value assigned to each species for each particular type of damage. For F. japonica % of properties with the species present includes those with a Knotweed plant within seven m of the main residential building (see Supplemental Information S2 ).

Fallopia japonica was not linked to any damage to the main buildings. The three other groups were linked to damage, at varying degrees, typically in the form of simple co-occurrence (e.g. as in appearing together without a clear causal link) or interference with brickwork through exacerbation of existing weakness. Mature woody B. davidii was more likely to exacerbate damage than immature B. davidii , with immature B. davidii rarely exceeding co-occurrence or minor exacerbation. There was only one example of a plant being linked to causing direct damage to a building, rather that exacerbating it. This was a tree falling against a house.

With respect to damage to walls, F. japonica was correlated with two occurrences of damage; in both cases it was emerging from a crack and causing no detectable variation away from baseline damage elsewhere in the wall. The three other plant groups were linked to more damage than F. japonica , to varying degrees, typically in the form of simple co-occurrence or interference with brickwork through exacerbation of existing weakness. In all groups, the average damage score was higher than that of F. japonica ( Table 4 ). Mature woody B. davidii was more likely to exacerbate damage than immature B. davidii , with immature B. davidii rarely exceeding co-occurrence or minor exacerbation. There were only two examples of a plant being linked to causing damage to walls, rather than exacerbating it, a tree pushing over a boundary wall and B. davidii pushing over a small retaining wall.

With respect to damage to paving, F. japonica was correlated with six occurrences of damage. In three cases it was emerging from a crack and causing no detectable variation away from baseline damage elsewhere in the paving, and in three other cases it was exacerbating existing damage (one minor, two moderate examples). B. davidii was linked to more damage to paving than F. japonica , typically in the form of simple co-occurrence or interference with paving through exacerbation of existing weakness. The average damage score was considerably higher for B. davidii than F. japonica . Mature woody B. davidii was more likely to exacerbate damage than immature B. davidii , with immature B. davidii rarely exceeding correlation or minor exacerbation. There was only one example of a plant being linked to causing damage to paving, rather that exacerbating it, which was a tree where the roots had lifted a large area of concrete paving with significant associated cracking.

Indirect damage: in the context of F. japonica

Plants are considered to cause structural damage to buildings primarily through indirect damage, for example through subsidence caused by modification to soil water content. High water-use tall trees are the main plant type implicated. Subsidence, with respect to plants, is only an issue on shrinkable clay soils, which are reasonably restricted in extent ( Fig. 1 ). Importantly, to properly assess risk, individual site investigation is required to determine the exact type of clay present in a clay–soil area. The rate that water is removed from soil by plants varies depending on the characteristics of the plant and also by the total biomass of the plant. There is a strong linear relationship between water use and plant biomass (i.e. larger plants remove more water from the soil), as noted by Nielsen et al. (2015) . Plants with higher water use and larger biomass are therefore the most likely to cause subsidence through the action of their roots removing water from soil. Some unpublished work suggests that F. japonica may be a high water use plant ( Vanderklein et al., 2013 ); however, even if this is the case, it is not a high biomass plant by comparison to mature woody trees such as oak. The plants that are most likely to influence subsidence in the UK are listed in the NHBC (2017) guidance for building near trees. These species range in height between 10 and 28 m. In comparison, F. japonica typically only grows to between two and three m. The potential for plants to influence subsidence is calculated based on a zone of influence of between 0.5, 0.75 and 1.25 times the height of the plant ( NHBC, 2017 ), depending on the water demand at maturity of the species in question (low, moderate or high, respectively). For F. japonica , this would suggest a maximum zone of influence of 3.75 m (the typical maximum height of the plant is three m, hence 3 × 1.25). However, when compared to mature trees, given the comparatively diminutive size of F. japonica , both in terms of above ground and below ground biomass, it is more likely to be at the lower end of the scale. As such, a calculation of 0.5 × 3 = 1.5 or 0.75 × 3 = 2.25 m is more likely to reflect the potential zone of influence of F. japonica at maturity. Furthermore, the mean rhizome length of small F. japonica stands, such as those more likely to be found in residential properties, is 1.4 m (‘Direct damage: in the context of F. japonica ’ and Fig. 4 ), which falls comfortably within the lower zone. Such areas of influence are unlikely to be able to create a large enough area of soil shrinkage to impact all but the flimsiest of structure and, even then, only on properties shown to have shrinkable clay soil. As such, the risk associated with F. japonica causing subsidence based damage falls well below many other species commonly found in properties in the UK.

Direct damage: in the context of F. japonica

In some situations, trees and vegetation can adversely affect structures by direct action, for example structural failure of trees (collapse and impact), impact of branches with superstructures, displacement/lift/distortion and disruption of underground services and pipelines ( British Standard, 2012 ).

The leading causes of damage due to direct physical contact by plants, that is collapsing vegetation striking buildings and power lines and branch impact, are not relevant in any meaningful way to F. japonica as the species is not tall enough and does not possess heavy enough aboveground structures. This is due to the fact that F. japonica aboveground material dies back at the end of each growth season; as such, the plant cannot accumulate sufficient above ground size and weight from successive years of growth.

Plants can also cause damage by exerting accumulating physical pressure on structures as they grow over time; however, as stated above, this is comparatively rare in terms of meaningful damage. Damage of this type is typically characterised by superficial or cosmetic damage to paving. However, more significant damage can occur where plants become trapped between two structures, for example two walls in close proximity to each other, and are allowed to exert pressure for an extended period of time without intervention (i.e. woody plants are allowed to mature in areas where management would be advisable) or where roots find their way into drains and pipes, as described above. The mechanisms by which plants grow and cause such damage are well understood ( Biddle, 1998 , 2001 ), as are the planting distances required to limit or avoid such damage ( British Standard, 2012 ). While F. japonica can cause such damage due to direct action over time, it does not exceed that caused by woody species. The case study described in this paper demonstrates that F. japonica is less capable of causing this type of damage than trees and woody shrubs. Where F. japonica is implicated in such damage, this is likely to typically be a result of the plant exploiting a weakness or defect that was already present, rather than the plant initiating the damage, or it is simply a case of F. japonica emerging from an existing crack without influence. Regardless, even if it is assumed that F. japonica can equal trees in causing such damage (which is not the case), based on well understood principles ( British Standard, 2012 ), a safe distance for mature F. japonica (crowns between 30 and 60 cm) would be 0.5 m for buildings and heavily loaded structures, and 1.5 m for paths and drives with flexible surfaces or paving slabs.

Additionally, the frequently stated ability of F. japonica to ‘grow through concrete’ is simply not supported by any evidence, as it is not possible due to the laws and principles of physics and biology. The extending tip of the F. japonica rhizome is remarkably soft and fleshy ( Fig. 1 ) and it would be impossible for it to grow through intact concrete; however, these same characteristics make the extending rhizome adept at finding cracks and F. japonica has been shown to have significant ability to alter the direction of rhizome growth ( Smith et al., 2007 ), highlighting the plant’s biological preference to go around obstructions, rather than through them. Where F. japonica is implicated in such damage, existing cracks or weaknesses are always present.

Typical rhizome extension

When the above is considered, the typical maximum rhizome extension of F. japonica is not all that relevant with respect to structural damage. Regardless, the results of the survey detailed above demonstrate that even large stands of F. japonica do not usually produce rhizomes that extend further than four m, showing that the ‘seven-m rule’ is not a statistically robust tool for estimating likely rhizome extension from above ground plants. The mean rhizome extent for small stands was 1.4 m and for large stands (above four m 2 ) was 2.02 m. Similarly, the mean vertical extent recorded averaged between 1.02 m for the small stands and 1.64 for the large stands, with a maximum of 3.2 m.

The biology of F. japonica makes it less capable of causing significant structural damage than many woody plant species. This conclusion has been reached for all three of the main mechanisms by which plants are known to cause structural damage: subsidence (indirect); collapse and impact (direct); and accumulating pressure due to growth (direct). There is essentially no support for F. japonica as a major cause of damage to property in the literature, and this study found that F. japonica is less likely to cause damage than other common species. Based on the results obtained though surveys completed by PCA members, it is clear that the ‘seven-m rule’ is not a statistically robust tool for estimating likely rhizome extension. F. japonica rhizome rarely extends more than four m from above ground plants and is typically found within two m for small stands and 2.5 m for large stands. When this is considered in conjunction with the water-use requirements of an herbaceous perennial, and the limited presence of shrinkable clay soils in the UK, the likelihood of F. japonica being a major cause of structural damage decreases even further. While F. japonica is clearly a problematic invasive non-native species with respect to environmental impacts and land management, this study provides evidence that F. japonica should not be considered any more of a risk, with respect to capacity to cause structural damage in urban environments, than a range of other species of plant, and less so than many. In this context, although the impacts of F. japonica on biodiversity and other ecosystem services remain a cause for concern, there is no evidence to support automatic mortgage restriction based on the species’ presence within seven m of a building.

Supplemental Information

Supplemental information 1.

Tab. 1: PCA member rhizome extent survey responses. Tab. 2: PCA member structural damage survey responses. Tab. 3: RICS member structural damage survey responses.

Supplemental Information 2

Tab. 1: Damage descriptors and Key for Tab. 2 nomenclature. Tab. 2: Case study damage assessment results.

Acknowledgments

We thank Prof Pippa Chapman, University of Leeds, for helpful discussion relating to soil properties; Chloe Spurgeon, AECOM/University of East Anglia, for supporting the literature assessment; Dr Damian Smith, AECOM, for supporting the assessment of the case study properties in the north of England; Andy Wakefield, AECOM, for support with respect to arboriculture; the Property Care Association for supporting the collection of contractor member Japanese knotweed impacts and rhizome extent data and all PCA members that provided such data; the Royal Institution of Chartered Surveyors for supporting the collection of surveyor Japanese knotweed impacts data and all RICS surveyors that provided such data; the Botanical Society of Britain and Ireland for permission to use their F. japonica map data in Fig. 1 ; and the British Geological Society for permission to use their shrinkable clay soil map in Fig. 1 .

Funding Statement

The authors received no funding for this work.

Additional Information and Declarations

The authors declare that they have no competing interests. Mark Fennell (Principal Ecologist) and Max Wade (Technical Director Ecology) are employed by AECOM, UK.

Mark Fennell analysed the data, prepared figures and tables, authored and reviewed drafts of the paper, approved the final draft, designed and co-ordinated the study.

Max Wade authored or reviewed drafts of the paper, approved the final draft.

Karen L. Bacon analysed the data, prepared figures and tables, authored and reviewed drafts of the paper, approved the final draft.

The following information was supplied relating to field study approvals (i.e. approving body and any reference numbers):

The site assessment, which was carried out by AECOM ecologists, was approved via an acceptance of a scope and quote letter and an agreement of Terms and Conditions. Given the socioeconomic impacts of Japanese knotweed presence in the UK, the location and client will be kept confidential.

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Japanese knotweed: the global menace — and a possible solution

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Japanese Knotweed

Photo credit: Dave Jackson

Japanese knotweed ( Fallopia japonica syn. Polygonum cuspidatum ), an herbaceous perennial member of the buckwheat family, was introduced from East Asia in the late 1800s as an ornamental and to stabilize streambanks. Knotweed is a highly successful invader of wetlands, stream corridors, forest edges, and drainage ditches across the country. Its close relative, giant knotweed ( Fallopia sachalinensis ), is very similar in appearance and ecology, and the two species form the hybrid bohemian knotweed ( Fallopia × bohemica ).

Description

Growing up to 11 feet tall, knotweed can spread horizontally via an extensive network of underground rhizomes, along which many shoots will sprout.

Superficially resembling bamboo, its jointed, hollow stem has many red or purple nodes where the leaves are attached. The stems are otherwise smooth, bright green, and often covered with darker spots or streaks. Portions of the stem bearing leaves appear to zigzag from node to node and form dense thickets.

Many alternately arranged, spade- or heart-shaped leaves emerge from nodes along the stem, though lower leaves are often shed as the plant grows. Japanese knotweed leaves can be up to 6 inches long and have a squared leaf base. Giant or hybrid knotweed leaves will grow much larger, up to 1 foot long, and have a rounded leaf base.

In late summer, white or pale green flower clusters sprout from the nodes. The fingerlike clusters are 3 to 4 inches long and consist of several dozen five-petaled, aromatic flowers.

Emerging in early spring, the young growth is especially bright red or purple and tipped with many furled leaves that are distinctly triangular.

$Closeup of Japanese Knotweed\'s white cluster of small flowers$

Look-alikes

Knotweed is often confused with bamboo (subfamily Bambusoideae), another invasive plant. Unlike knotweed, bamboo has slender, papery leaves that persist year-round. In cross-section, bamboo stems are also jointed, but much woodier, while living knotweed stems are herbaceous and will be visibly wet upon cutting. Another nonnative but not aggressively invasive species, broad-leaved dock ( Rumex obtusifolius ), could also be confused with young knotweed shoots, but broad-leaved dock consists of a rosette of many basal leaves emerging from a central taproot, differentiating it from Japanese knotweed's many single, rapidly elongating stems.

The key to Japanese knotweed's success is its ability to spread vegetatively through its root system. While some populations also reproduce via seed, colonies of knotweed are usually formed from an interconnected, underground system of horizontal roots called "rhizomes." These rhizomes are prone to splitting when disturbed and each fragment is capable of forming a fully functional clone of the parent plant. Fragments can be dispersed along waterways during flooding events or by the movement of soil containing root fragments. Additionally, if stems are cut, both the still-rooted stem and the trimmed portion are capable of regrowing into new plants if in contact with moist soil. Due to these traits, knotweed stands are extremely persistent even after multiple removal attempts.

This plant thrives on most sites that are at least seasonally wet. However, it can tolerate a wide variety of growing conditions, including acidic mine spoils, saline soils adjacent to roads, and fertile riverbanks. Though somewhat intolerant of shade, it can persist along forest edges or in the shade of bridges and road structures. The dense, low canopy formed by a thicket of tangled stems and large leaves creates a monoculture, excluding nearly all other vegetation. In comparison to native streamside vegetation, Japanese knotweed provides poor erosion control, and its presence gradually degrades aquatic habitat and water quality.

The primary objective in controlling Japanese knotweed is eliminating the rhizome system. Rhizomes are creeping underground stems that give rise to new shoots and roots. As long as you are willing to invest the effort and follow a few key timing guidelines, it can be successfully controlled.

There are two phases of knotweed management: initial control and maintenance. The control phase for knotweed takes at least two seasons and consists of either two applications of herbicide or a cutting with a follow up of herbicide. Late season application of herbicide in the control phase is especially effective because this is when the foliage is sending sugars produced through photosynthesis to the roots and rhizomes; systemic herbicides move through the plant with those sugars. After initial control efforts have nearly eliminated the knotweed, you will need to periodically monitor the site and treat any new growth to prevent reinfestation.

Cutting alone is not an effective suppression approach. However, cutting prior to an herbicide application can be very helpful. Cut in June and wait at least eight weeks after cutting to treat the resprouting plants with herbicide; knotweed regrowth will be much shorter than if it had not been cut, and the rhizomes will be forced to redirect their energy reserves toward resprouting instead of expanding their underground network. Typically, knotweed regrows to 2 to 5 feet tall during the eight-week window after cutting, but this waiting period is critical—if you apply herbicide too soon after cutting, the herbicide will not be effectively translocated to the rhizomes. Cutting is also useful when knotweed is growing near water because it is easier to treat the shorter regrowth without inadvertently spraying herbicides into the water during follow-up treatments. Treating intact knotweed towering over your head can be difficult, but cutting may be even more work. As long as you are able to effectively spray all the foliage, cutting is not critical. Wait at least eight weeks after cutting before applying herbicide.

We recommend glyphosate, a nonselective herbicide available as aquatic-labeled products for use in or near water. Glyphosate is effective, has low toxicity to nontarget organisms, has no soil activity, and is relatively inexpensive. The herbicide imazapyr (e.g., Polaris, Habitat) is also effective against knotweed, but it has considerable soil activity and can injure nearby trees through root uptake. Broadleaf herbicides such as triclopyr or 2,4-D provide significant foliar injury but have limited effect on the rhizome system. Mixing glyphosate with other herbicides makes sense if knotweed is not your only target during spray operations. Combinations with triclopyr or imazapyr provide a broader species spectrum and do not reduce activity against knotweed.

Management Calendar

The management calendar for knotweed emphasizes late season applications of the herbicide glyphosate to maximize injury to the rhizomes and waiting at least eight weeks after cutting to apply herbicide.

Treatment and Timing

Prescriptions for controlling knotweed stress proper timing of operations to maximize injury to rhizomes. Improper timing will result in treatments that provide "topkill" (shoot injury) but little net effect. Product names reflect the current Pennsylvania state herbicide contract; additional brands with the same active ingredients are available.

Treatment	Timing	Herbicide	Product Rate	Comments
Preherbicide cutting	June	N/A	N/A	Cutting in June results in shortened regrowth (2 to 5 feet) and elimination of persistent stems from the previous season. This is a particular advantage in riparian settings, where full-size knotweed will hang over the water, making it impossible to treat without contacting the water with herbicide solution.
Foliar	At least eight weeks after cutting as a follow-up treatment or after late spring frosts for a treatment plan without cutting	Aquaneat or Glyphomate 41 (glyphosate)	3 quarts/acre or 4.3 quarts/acre	Use any of these glyphosate formulations to treat knotweed foliage, waiting eight weeks after cutting or a late frost to treat. The product rates differ because the glyphosate concentration differs between products. Applications of Aquaneat will require an additional surfactant (e.g., CWC 90). No additional surfactant is needed with Glyphomate 41. If you work at the early end of the operational window, you can make a touch-up application later in the season before a killing frost. Use this treatment for both initial control and follow-up maintenance applications. For high-volume (spray-to-wet) applications, mix on a 100 gallon-per-acre basis (e.g., Aquaneat would be 96 ounces per 100 gallons, or 0.75 percent by volume). For all treatments, be sure to calibrate your sprayer.

All species of knotweed found in the United States produce edible young shoots in spring. Knotweed honey is a popular monoculture honey, as its fragrant, nectar-rich blossoms are a favorite of our nonnative honey bee (Apis mellifera). In its native Asia, knotweed has many applications in traditional herbal medicine. While these human uses are often raised in argument against controlling Japanese and other knotweeds, none outweigh the consequences of unchecked knotweed infestation. Knotweed infestations result in decreased biodiversity in both plant and animal communities, degraded water quality, and damage to human infrastructure such as road and bridge foundations. These widespread and highly negative effects should be considered alongside any argument for its overall value.

Prepared by Skylure Templeton, Art Gover, Dave Jackson, and Sarah Wurzbacher. Reviewed by Norris Muth, Amy Jewitt, and Andrew Rohrbaugh.

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Terrestrial Invasives
Terrestrial Plants

Japanese Knotweed

Fallopia japonica (Houtt.) Ronse Decr. ( ITIS )

Japanese knotweed, fleeceflower, Mexican bamboo, huzhang

Polygonum cuspidatum Siebold & Zucc.; Reynoutria japonica Houtt.

Asia ( Stone 2010 )

Late 1800s ( Stone 2010 )

Introduced as an ornamental ( Stone 2010 )

Crowds out native species ( Stone 2010 )

Japanese knotweed, foliage

Photo by Jack Ranney; University of Tennessee

Find more images

Google Images - Japanese Knotweed
Invasive.org - Japanese Knotweed

Distribution / Maps / Survey Status

Early detection & distribution mapping system (eddmaps) - japanese knotweed.

University of Georgia. Center for Invasive Species and Ecosystem Health.

Provides state, county, point and GIS data. Maps can be downloaded and shared.

YouTube - How to: ID and Manage Invasive Knotweeds

Google. YouTube; Invasive Species Council of British Columbia (Canada).

All Resources

Selected resources.

The section below contains highly relevant resources for this species, organized by source.

Invasive Plants of Ohio: Fact Sheet 10 - Japanese Knotweed [PDF, 254 KB]

Ohio Invasive Plants Council.

See also: Invasive Plants of Ohio for worst invasive plant species identified in Ohio's natural areas

Priority Species: Japanese Knotweed

Washington State Recreation and Conservation Office. Washington Invasive Species Council.

Southeast Exotic Pest Plant Council Invasive Plant Manual - Japanese Knotweed

Southeast Exotic Pest Plant Council.

Alaska Exotic Plants Information Clearinghouse (AKEPIC): Species Biography - Japanese Knotweed, Giant Knotweed, Bohemian Knotweed [PDF, 304 KB]

Feb 7, 2011

University of Alaska - Anchorage. Alaska Center for Conservation Science.

See also: Non-Native Plant Species List for additional factsheets (species biographies) and species risk assessment reports of non-native species present in Alaska and also non-native species currently not recorded in Alaska (potential invasives)

Global Invasive Species Database - Fallopia japonica (herb, shrub)

IUCN . Species Survival Commission. Invasive Species Specialist Group.

Invaders Factsheet: Japanese Knotweed

Ontario's Invading Species Awareness Program (Canada).

Invasive Plant Atlas of the United States - Japanese Knotweed

Invasive species compendium - fallopia japonica.

CAB International.

Japanese Knotweed Alliance

New york invasive species information - japanese knotweed.

New York Invasive Species Clearinghouse.

Non-native Species Information: Japanese Knotweed

Great Britain Non-Native Species Secretariat.

Weeds Australia - Japanese Knotweed ( Fallopia japonica )

Centre for Invasive Species Solutions; Atlas of Living Australia; Australian Government. Department of Agriculture, Water and the Environment.

Biology and Biological Control of Knotweeds [PDF, 13.34 MB]

USDA . FS . Forest Health Technology Enterprise Team.

FHTET-2017-03. See also: FHAAST Publications for more resources.

Fire Effects Information System (FEIS) - Polygonum sachalinense, P. cuspidatum, P. × bohemicum

USDA . FS . Rocky Mountain Research Station. Fire Sciences Laboratory.

National Exotic Marine and Estuarine Species Information System (NEMESIS): Chesapeake Bay Introduced Species Database - Polygonum cuspidatum

Smithsonian Institution. Smithsonian Environmental Research Center. Marine Invasions Research Lab.

PLANTS Database - Japanese Knotweed

USDA . NRCS . National Plant Data Center.

U.S. National Plant Germplasm System - Reynoutria japonica

USDA . ARS . National Genetic Resources Program. GRIN-Global.

Invasive Plants - Japanese Knotweed

Cornwall County Council (United Kingdom).

Fact Sheet: Japanese Knotweed ( Polygonum cuspidatum ) [PDF, 237 KB]

New Hampshire Department of Agriculture, Markets, and Food. Division of Plant Industry.

See also: New Hampshire's Prohibited Invasive Plant Fact Sheets for additional invasive trees, shrubs, vines, and herbaceous plants

Invasive Species Best Control Practices - Japanese Knotweed [PDF, 373 KB]

Michigan Department of Natural Resource; Michigan State University Extension. Michigan Natural Features Inventory.

See also: Best Control Practice Guides for more guides

Invasive Plant Species Fact Sheet: Japanese Knotweed [PDF, 734 KB]

Indiana Department of Natural Resources. Invasive Plant Species Assessment Working Group.

See also: Species Assessments and Invasive Species for exotic animal and plant pests invading Indiana, causing economic and visual damage

Class B Noxious Weed: Japanese Knotweed

Washington State Noxious Weed Control Board.

Encycloweedia: Data Sheet - Fallopia genus

California Department of Food and Agriculture.

See also: Included on California's noxious weed list; see Encycloweedia: Program Details for additional resources

Field Guide: Invasive - Japanese Knotweed

Missouri Department of Conservation.

Invasive Plants in Pennsylvania: Japanese Knotweed and Giant Knotweed [PDF, 162 KB]

Pennsylvania Department of Conservation and Natural Resources.

See also: Invasive Plant Fact Sheets for plant species (trees, shrubs, vines, herbs and aquatic plants) that have impacted the state's natural lands

Japanese Knotweed ( Polygonum cuspidatum )

Wisconsin Department of Natural Resources.

King County (Washington) Noxious Weed Control Program - Japanese Knotweed

King County Department of Natural Resources (Washington). Water and Land Resources Division.

Noxious Weed Species ID - Japanese, Giant, and Bohemian Knotweeds

Colorado Department of Agriculture. Conservation Services Division. Noxious Weed Program.

MontGuide - Biology, Ecology and Management of the Knotweed Complex

Montana State University Extension.

Biology and Managementof Knotweeds in Oregon:A Guide for Gardeners and Small-Acreage Landowners

Oregon State University. Extension Service.

Insects, Pests, and Diseases: Japanese Knotweed

Pennsylvania State University. Cooperative Extension.

Introduced Species Summary Project - Japanese Knotweed

Columbia University. Center for Environmental Research and Conservation.

Ohio Perennial & Biennial Weed Guide - Japanese Knotweed

Ohio State University. Ohio Agricultural Research and Development Center.

Knotweeds ( Fallopia spp.) - History and Ecology in North America [PDF, 7.62 MB]

North American Invasive Species Management Association.

See also: Biocontrol Factsheets for more information on biocontrol agents

Integrated Taxonomic Information System. Fallopia japonica . [Accessed Sep 16, 2023].

Stone, K.R. 2010. Polygonum sachalinense, P. cuspidatum, P. × bohemicum . In: Fire Effects Information System. U.S. Department of Agriculture, Forest Service, Rocky Mountain Research Station, Fire Sciences Laboratory.

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Japanese Knotweed: New research into tackling invasive weed as annual damage calculated at £165 million

This article contains affiliate links. We may earn a small commission on items purchased through this article, but that does not affect our editorial judgement.

New research into the long-term environmental impact of the methods used to control Japanese knotweed has been published. The invasive species can cause widespread damage to buildings and gardens.

Weed removal specialists Complete Weed Control has part funded research at Swansea University. It comes as the calculated cost of damage caused by knotweed is estimated to be £165 million.

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In efforts to tackle the problem, various techniques have been developed. However, with sustainability becoming increasingly important, understanding the effect of these management methods is vital.

A new study, led by biosciences lecturer Dr Sophie Hocking and looking at the entire life cycle and long-term impacts of different management approaches, has just been published in online journal Scientific Reports .

Dr Hocking said: “In light of the current climate emergency and biodiversity crisis, invasive species management and sustainability have never been so important.

“Both of these are intrinsically linked – we know that invasive species can cause substantial negative ecological, social and economic impacts, and the way we manage these species should mitigate against this in a sustainable way to ensure we are not doing more harm than good.

“Although there has been more research into how we can best manage the plant, little is known about how sustainable these approaches are.”

Gardeners beware - Japanese knotweed is extremely destructive

Ian Graham, managing director of Complete Weed Control, stressed the significance of using science to inform best practice adding: “Industry is responsible not only for delivering high-quality outcomes but also for doing so in a manner that takes environmental and social factors into account. This new study will help inform us, ensuring our methods remain the most sustainable.”

“I am proud to say that our organisation is widely recognised for delivering the highest level of service to our customers across the UK and Ireland, with a strong commitment to continuous improvement and meeting environmental requirements.

“This latest partnership with Swansea University and Advanced Invasives aligns with our commitment to investment in research and technology and our dedication to excellence and sustainability within the industry."

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Japanese Knotweed is most often used for .

Japanese Knotweed

Japanese Knotweed, or Polygonum cuspidatum , is a Traditional Chinese Medicine used for circulation and heart health. It is a very good source of resveratrol , and most benefits of Japanese Knotweed may actually just be benefits of resveratrol .

Last Updated: November 18, 2022

Sources and Composition

Composition

Structure and Properties

Pharmacology

Distribution

Enzymatic Interactions

Immunology and Inflammation

General inflammation

Common Cold

Neurology and the Brain

Interactions with Hormones

Interactions with Body Weight

Interactions with Aesthetics

Polygonum Cuspidatum is a herb in the polygonaceae family (alongside Rheum palmatum L and the similar plant Polygonum multiflorum ) and the genera of Fallopia ; it is native to eastern China and Japan and is sometimes (most commonly) referred to as Japanese Knotweed. Polygonum Cuspidatum has been used traditionally for its medicinal qualities, specifically treatment of artherosclerosis as well as cancer, asthma, hypertension, and cough.

Traditional usage in China is associated with the name Hu Zhang or Hu Chang , and traditional usage in Japan is associated with the name Kojo Kon . Japanese Knotweed (and other terms, such as Mexican or Japanese Bamboo) are more commonly used in North America. [1]

There are three variants of Polygonum Cuspidatum ; namely Polygonum Cuspidatum var. Japonicus, var. sachalinensis, and var. bohemica. These variants differ in quantities of bioactives, [2]

Interestingly, Japanese Knotweed is seen as an invasive plant species and causing problems in a variety of areas in the globe. [3] [4] [5]

Its simple, we eat the knotweed and save the other plants

The following molecules are found in the three variants of Polygonum Cuspidatum, but the quantities specified below are specific to var. Japonicus; this variant tends to be highest in stilbenes, with minimal levels in the other two species. [2]

Focus on the stilbenes (first four bullets) and the quinones (bullets 5-8) as the active ingredients; the other compounds are found in the herb, but either to lesser amounts or are not the focus of current research

Resveratrol [6] varying from 0.15-1.77mg/g dry weight
Piceid (5,4'-dihydroxystilbene-3-O-β-D-glucopyranoside), a glucoside of resveratrol [7] at around 9.91-16.4mg/g dry weight, and Polydatin (aka. Polygonin or 3,4',5-trihydroxystilbene-3-β-single-D-glucoside) another glucoside of Resveratrol [8]
Piceatannol (a stilbene related to Resveratrol ) and its glucoside, Astringin [2] at 0.025-0.067mg/g and 0.98-1.22mg/g; respectively [2]
Resveratroloside, a structure that is a glucoside of resveratrol but at a different spot than Piceid [9]
Anthraquinones such as Rhein and Physcion; but mostly Emodin [10] [11] as well as their glucosides [12] At 35.3mg (Emodin) and 8.2mg (Physcion) from 6.7g dry extract, and 17.6mg (anthraglycoside B) from 4.6g dry extract; 5.2mg/g, 1.2mg/g, and 3.8mg/g respectively. [13]
The anthraquinone Chrysophanol/Chrysophanic acid [14] [15] which may protect from colon carcinogenesis [16]
Anthraquinone derivatives such as Citreorosein [17]
The _Naptho_quinone compound 2-Methoxystypandrone [18] more officially known as 2-methoxy-6-acetyl-7-methyljuglone; [19] found at 1mg per 100g chloroform extract [20]
5,7-Dimethoxy-isobenzofuran-1(3H)-one(aka. 5,7-dimethoxyphthalide) [21]
Tachioside [22]
Tryptophan [22]
2,6-dihydroxybenzoic acid [22]
Gallic Acid [22]
(+)- catechin (one of the Green Tea Catechins ) and a glucoside, (+)- catechin-5-O-β-D glucopyranoside [22]
1-(3-O-β-D-glucopyranosyl-4,5-dihydroxyphenyl)-ethanone [22]

Overall, a phenolic content of 641.1 +/- 42.6 mg/g (60-68%) and a flavonoid content of 62.3 +/- 6.0 mg/g (5.4-6.8%) has been reported for the dry weight of general Japanese Knotweed extract. [23]

Resveratrol and its glucoside piceid range from 0.04-0.1mg/g and 0.2-0.51mg/g in Polygonum Cuspidatum var. sachalinensis , while piceatannol and its glucoside Astringin range from 0.006-0.008mg/g and 0.04-0.22mg/g, respectively. [2] Polygonum Cuspidatum var. bohemica ranges from 0.08-0.95mg/g, 1.72-7.32mg/g, 0.01-0.095mg/g, and 0.31-1.87mg/g for resveratrol, piceid, piceatannol, and astringin respectively. [2] Put collectively, Japonicus is the standard and appears to be best while bohemica can potentially be competitive and sachalinensis possesses much less stilbenes than the other two variants.

Resveratroloside appears to be similar in content to piceatannol when measured. [9]

The wide range of content for the stilbenes (resveratrol and piceatannol) vary both depending on species as well as between samples of the same species; quite an unreliable content. As for what a 'glucoside' or 'glycoside' are, they are storage forms of the parent molecule which may or may not also be absorbed and thus be bioactive; piceid is literally a resveratrol molecule bound to a glucose molecule

The following structures are the four (most commonly researched) stilbenes found in Japanese Knotweed; the stilbene resveratroloside looks the same as piceid except with the glucose moiety bound to the 4' carbon rather than the 3 carbon (other hexagon of the structure, on the opposite side of the middle chain). Polydatin is also similar, in the fact that its glucose moiety is bound to the 5' carbon (one below the 4'). [24]

Resveratrol and its glucoside Piceid appear to be structurally stable when exposed to light and the open environment (room temperature) for up to three months, [25] although stability of resveratrol in Japanese knotweed insulted by environmental stressors is not as good; [26] prudency and good storage should still be practised.

In general, Japanese Knotweed extract possesses moderately potent anti-oxidant capabilities, [23] second to the species of capitatum but higher than chinensis and multiflorum as assessed in vitro . [27] The anti-oxidant capacity of Polygonum Cuspidatum has been reported to be 56.22mmol/100g Trolox equivalents and 6.33g/100g Gallic acid equivalents, and has been shown to extend to the leaves and stems as well as the roots. [27] According to this study [28] which analyzed 112 herbs and summed up that anti-cancer herbs from Traditional Chinese Medicine tend to have higher anti-oxidative capacities than common fruits and vegetables, it was found that (according to Trolox equivalents of the methanolic extract, a way to measure anti-oxidant potential) Japanese knotweed placed 14 th out of 112, with 35% of the potency (on a gram to gram basis) as Camellia Sinensis , the most common source of Green Tea catechins and 5 th place overall. The winners were the gall of Rhus chinensis and the branch/stem of Acacia catechu , with 3.28x and 2.12x greater anti-oxidative effects relative to Camellia Sinensis , respectively. [28]

Three main classes of compounds, and their content and individual anti-oxidant potential is pretty good relative to other herbs out there

Resveratrol has had its pharmacokinetics analyzed on its own page; a short summary is that oral ingestion of resveratrol has poor bioavailability but it can be enhanced with consumption of other nutrients alongside it.

Distribution of resveratrol after oral administration (20mg/kg) in rats appear to reach the heart (up to 743.4+/-45.77ng/mL) yet are excreted almost completely by 60 minutes, the liver at around 2mcg/mL (2,000ng/mL) for up to 60 minutes, up to 2.8mcg/mL in the lung tissue at 60 minutes yet almost undetectable prior, moderate amounts in the kidney (0.8-1.3mcg/mL) between 30-60 minutes, with most being detected in the stomach and none in the brain at up to 60 minutes. [29] This is similar distribution data found in mice given isolated resveratrol, [30] [31] except none was found in the brain in this study; the lack of finding resveratrol in the brain, as well as the high (48.2mcg/mL) content in the stomach may be due to the study terminating at 60 minutes. [29]

Similar to Resveratrol in isolation, the resveratrol from Polygonum Cuspidatum appears to be highly conjugated with minimal free resveratrol being excreted in the urine. [29] 0.059% of the oral dose was found in the urine unconjugated, and 0.027% was found in the bile unconjugated; leaving 99.14% of the oral dose of resveratrol either excreted as a conjugate or distributed into a tissue 24 hours after oral administration. [29]

Polygonum Cuspidatum appears to be able to inhibit both the CYP3A enzyme as well as the efflux protein 'MultiDrug Resistance Protein 2' (MRP2) [32] and may interact with pharmaceuticals such as carbamazepine that are metabolized by these enzymes. In an investigation into whether Resveratrol from Japanese Knotweed could upregulate CYP3A4 via CAR, it was found to not possess this capability. [33]

The one human study conducted using Japanese Knotweed found that, after 6 weeks supplementation of 200mg (40mg Resveratrol) daily, that extracted immune cells had 25% less translocation of NF-kB; NF-kB is a mediator of inflammation , and this was overall a reduction in inflammation. [34] The reduction in NF-kB activity resulted in less circulating TNF-a and IL-6 as well; two inflammatory cytokines. [34] Large doses in animals (100-200mg/kg ethyl acetate fraction) have been shown to induce anti-inflammatory effects acutely, and showed promise in an animal model of rheumatoid arthritis. [35]

The napthaquinone from Japanese Knotweed has been demonstrated to be a potent inhibitor of the HRV 3C-protease enzyme with an IC 50 of 4.6uM. [20] This enzyme is required for replication of the Rhinovirus, which is the most common agent for the common cold; [36] thus inhibitors are being investigated for reducing the occurrence of and severity of the common cold, such as rupintrivir (AG-7088). [37]

Emodin, the anthraquinone compound, is being investigated for its ability to suppress activation of mast cells via preventing IgE from associating with FcɛRI. The binding of IgE to FcɛRI on mast cells is the first stage of the anaphylactic response on mast cells, [38] and eventually results in histamine release. Emodin seems to inhibit this response dose-dependently after oral administration of 5-40mg/kg bodyweight [39] and Japanese Knotweed extract appears to be quite effective as well, with an IC 50 value of 62+/-2.1ug/mL on mast cells. [40]

Interactions with Japanese Knotweed and reducing allergies, potency of this effect in humans is not known; may extend to topical usage for nickel dermatitis

Polydatin, or the glucoside of resveratrol, has been shown to protect rats from cognitive decline in a model of dementia when supplemented over 30 days at 12.5, 25, and 50mg/kg bodyweight orally. [24] 25mg/kg Polydatin was slightly less protective than 25mg/kg Ginkgo Biloba , but insignificantly so. [24] Resveratrol from Japanese Knotweed also shows benefit itself at 20mg/kg oral ingestion. [41]

Napthaquinones from Japanese Knotweed do show protective effects as well in vitro , secondary to their anti-oxidant effects. [19] Oxidative damage was completely abolished, and cell viability actually increased above control at the higher concentrations tested (2.5uM, 5uM; 0.05-1uM protected but did not increase viability above control). [19]

Emodin has been demonstrated to protect neurons from damage in vitro , but these results may not be practically relevant as emodin possesses a low bioavailability. [42]

Although the doses requires to show neuroprotection are high (20mg/kg resveratrol, 12.5mg/kg polydactin) there appear to be multiple neuroprotective compounds; whether this is better or worse than isolated but more potent compounds is not known

In a study on 32 traditional Chinese plants, it was found that Japanese Knotweed was the most potent with an EC 50 value of 6.4ug/mL. [43] Other herbs that were found to be slightly estrogenic were Horny Goat Weed (EC 50 of 100ug/mL), Astragalus membranaceus (EC 50 of 236.1ug/mL), Belamcanda chinensis (EC 50 of 142.8ug/mL) and second place went to Rheum palmatum (EC 50 of 46.7ug/mL) ; all 70% ethanolic extracts and assessed in bacteria expressing the estrogen receptor. [43] 17β-estradiol itself had an EC 50 of 0.205ng/mL, for comparison. [43]

The active molecules behind this estrogenicity may be the anthraquinone content, [44] although they appear to inhibit binding of 17β-estradiol to its receptor when coincubated and may act as both agonists (during estrogen deficiency) and competitive antagonists (during estrogen surplus). [44] However, emodin (the most prominent anthraquinone) has an EC 50 of 10.1+/-0.36 ng/mL [45] while the whole knotweed was more effective at 6.4ug/mL. [43] suggesting there is another compound with potency estrogenic effects. One study dividing fragments of Polygonum saw that the fragment with the most emodin (Hzs1) was matched by one with no emodin content (Hzs6), and this was contributed to an unknown compound. [45]

Seems to be a phytoestrogenic compound in vitro , but anthraquinones usually have low bioavailability (percentage absorbed in the intestines; hence why they make good laxative compounds) and so this estrogenicity may not be practically relevant

After 6 weeks of supplementation of 200mg Japanese Knotweed (containing 40mg resveratrol) daily, no significant effects were observed on body mass or circulating leptin levels. [34]

Japanese knotweed has been shown to somewhat permeate the skin, [46] and thus its usage as a cosmetic agent for topical application has been investigated.

When tested in melanocytes (melanin producting cells under the skin), a component in Polygonum called Piceid is able to inhibit tyrosinase activity in a dose-dependent manner [7] and may act as a skin lightening agent. Piceid is not a potent inhibitor of tyrosinase directly [47] but appears to suppress mRNA and subsequent protein content of tyrosinase. [7] Resveratrol also possesses an indirect inhibitory mechanism, as Resveratrol is a substrate for tyrosinase and its metabolites then accumulate and inhibit activity. [48] [49] Piceatannol , also a component of Japanese Knotweed, can suppress melanogenesis via tyrosinase by its anti-oxidant effects, and like Piceid it can downregulate melanin content [50] and Emodin, the anthraquinone, can suppress tyrosinase activity directly [51] although the related anthraquinone physcion is more potent and had 48 times more dermal penetration. [52]

Beyond lightening, Japanese Knotweed has been shown in rats to accelerate wound healing and enhance the quality of the repaired wound relative to an untreated control. [53] Anti-inflammatory effects of Polygonum Cuspidatum have also been seen when applied topically, mostly due to the trans- resveratrol content. [54]

Eradication of the biofilms produced by the bacteria Propionibacterium acnes , which plays a role in acne, can also be done by Resveratrol ; by extension, Japanese Knotweed may alleviate acne when topically applied. [55] Interestingly, this study extends to both Rhodiola Rosea via Salidroside and Horny Goat Weed via Icariin.

Possibly by pure changes, compounds in Japanese Knotweed appear to all inhibit tyrosinase activity via different mechanisms and may be highly synergistic with each other when applied topically; this has not been tested, however. Japanese Knotweed does appear to reduce inflammation when topically applied, and may reduce both acne and nickel dermatitis as well (although these leads need more evidence to fully validate)

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Japanese Knotweed

Author: Sandy Vanno, Master Gardener Warren County CCE

Japanese knotweed (Polygonum cuspidatum), a member of the buckwheat family is a native of Asia and was first introduced to England in the early 19 th century as an ornamental plant. It was later introduced into the United States for erosion control, and on Long Island as an estate-grown ornamental, due to its attractive foliage and cream-colored inflorescence. By the mid-1890s it was reported near Philadelphia, PA, Schenectady, NY, and in New Jersey. Although once sold through seed and plant catalogs, by the late 1930s knotweed, was already being viewed as a problematic pest. It is now widespread throughout New York State and most of the United States.

Knotweed is often confused with bamboo (subfamily Bambu-soideae), another invasive plant. Unlike knotweed, bamboo has slender, papery leaves that persist year-round. Bamboo stems are also jointed, but much woodier while living knotweed stems are herbaceous and will be visibly wet upon cutting. Japanese knotweed stems are hollow and jointed. The leaves are alternate, broadly egg-shaped, and 3 to 6 inches in length. The plant is dioecious, so male and female plants both produce cream-colored flowers that vary slightly in appearance. Flowers appear in late summer and are found in erect clusters 4 to 5 inches long arising from the leaf axils. It can most commonly be found in moist, unmanaged areas, including riverbanks and riparian sites, sodded storm drains and ditches, roadsides, and unkempt gardens. It tends to flourish on moist, well-drained, nutrient-rich soil, especially on shaded banks. Recently it has appeared more frequently along with sunny, dry roadside locations, suggesting the plant is adapting to diverse environments. It creates a dense canopy that prevents the growth of native plants, allowing it to dominate large areas of land. It has the potential to increase soil erosion on riparian banks and flooding potential. Knotweed shoots can also push up through roads, sidewalks, and foundations.

Management of Japanese knotweed typically requires several years and becomes very expensive. One of the best ways to prevent its colonization is to ensure that disturbed habitats are rehabilitated with native vegetation before knotweed can invade. However, if it does invade, digging or pulling can control, or locally eradicate early infestations. Integrated management incorporating chemicals may be more effective for larger infestations.

Management strategies:

digging and pulling – requires all roots and runners be removed; special care must be taken to avoid missing any roots or rhizomes; should only be done for mature stems, ensuring that it is pulled from the base of the stem; deep digging for well-established plants lead to a significant increase in stem density but if it is integrated with herbicide treatments it can be effective.
cutting and mowing – well suited for houses, resorts and lawn borders, parks, and gardens – cutting stems in early summer followed by herbicide application can improve the effectiveness of treatment. Some suggest against this treatment as there is less leaf area for herbicide treatment than knotweed that is left alone; also, it is difficult to time mowing properly.
biocontrol – A phalara itadori is a species of psyllid from Japan that feeds on Japanese knotweed and may reduce the growth rate; this biocontrol was released in the UK in 2010 and Canada in 2014 and has been approved for release within the US.
chemical control – systemic herbicides are generally the most efficient and effective means of managing knotweed due to the chemicals being trans-located to rhizomes following foliar applications; the ideal time to apply an herbicide is when flower buds are developing in August or September after-stems were cut in late spring or early summer; after treatment, all dead stems should be knocked down to ensure easy access for future management; significant decreases in Japanese and hybrid knotweed abundance can be achieved by different combinations of herbicides; however, there is no robust evidence available regarding their long-term effectiveness.
disposal – plant material must be removed and disposed of properly because the stems and rhizomes can resprout; solarized biomass in a bag in the sun for at least two weeks or plant material can be spread on a contained, impervious surface in a thin, even layer to ensure even heating. Contaminated soil and plant material should be buried at least 5 feet under the surface in a disposal pit with annual monitoring to ensure there is no regrowth; if necessary, re-sprouting plants can be treated with herbicides; this material should no t be composted. Stem and other plant material could be burned to ensure there is no regrowth and then put into a landfill. For contaminated soil, the environmental agency waste regulation department should be contacted or disposal can be in situ, to reduce landfill charges and decrease the risk of spread and ensure that the effectiveness of the disposal can be monitored. It is extremely important to tamp down soil after removing plants. The key is to avoid plant material from making contact with any type of watercourse. Always inspect your shoes and clothes before leaving your garden if it is contaminated with knotweed. Ensure you don't carry any plant or oil material from your garden. You can easily spread the knotweed to other parts of your garden.

For more detailed information on Management Strategies, and a detailed list of herbicide treatments and application time for sites near water and away from water, please refer to the document “Japanese Knotweed ( Reynoutria japonica) : Best Management Practices”, published by New York Invasive Species Research Institute and Cornell College of Agriculture and Life Sciences.

Japanese knotweed strikes fear into the hearts of homeowners in England, as its presence can threaten their property's foundations and make it almost impossible to sell or remortgage. Standard household insurance policies refuse to cover the damage. Due to the amount of damage knotweed causes, if it's discovered at a property as a result of a normal mortgage valuation or property survey, many lenders will either refuse a mortgage altogether or impose specific criteria if they do decide to proceed at all. Under Environmental laws in England, failure to control the spread of the plant can result in civil nuisance claims which can mean legal action and heavy financial penalties. Knotweed can also reduce the value of a property in England between £25,000 and £50,000 if knotweed is formally identified by a surveyor. There is a growing concern in the United States.

References:

CCE Oneida County; Japanese Knotweed

Cornell University Press; “Weeds of the Northeast”

New York Invasive Species Clearinghouse Species Profile “Japanese Knotweed”

Penn State Extension; Invasive Plant Fact Sheet “Japanese Knotweed”

NY Invasive Species Research Institute; Cornell College of Agriculture and Life Sciences; “Japanese Knotweed: Best Management Practices”

https://www.express.co.uk/finance/personalfinance/...

Last updated November 9, 2021

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New approaches on japanese knotweed ( fallopia japonica ) bioactive compounds and their potential of pharmacological and beekeeping activities: challenges and future directions.

1. Introduction

2. phyto-chemical constituents and identification methods, 3. biological activities, 3.1. antibacterial activity, 3.2. antioxidant activity, 3.3. anticancer, antiproliferative and apoptotic activity, 3.4. anti-inflammatory and antiviral activity, 3.5. other bioactive properties, 4. future directions, 4.1. fallopia japonica flowers: important nectar source, 4.2. knotweed honey, 4.3. comparison with other honey types from the same plant family, 5. conclusions, author contributions, institutional review board statement, informed consent statement, conflicts of interest.

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Root extract of R. japonica China (R.j.C); R. japonica Poland (R.j.P); R. x bohemica (Rxb) R. sachalinensis (R.s.)	HPLC-DAD- HR-MS gradient mode	water-formic acid (100:0.1 v/v) (solvent A) acetonitrile-formic acid (100:0.1 v/v) (solvent B)	- piceid (14.83 mg/g R.j.C; 7.45 mg/g R.j.P; 4.67 mg/g Rxb) - resveratrol (1.29 mg/g R.j.C; 0.65 mg/g R.j.P; 0.52 mg/g Rxb) - vanicoside B (0.64 mg/g R.j.C; 0.49 mg/g R.j.P; 0.77 mg/g Rxb; 2.25 mg/g R.s.) - vanicoside A (0.08 mg/g R.j.C; 0.04 mg/g R.j.P; 0.12 mg/g Rxb; 0.55 mg/g R.s.) - emodin (4.93 mg/g R.j.C; 4.01 mg/g R.j.P; 1.93 mg/g Rxb; 0.13 mg/g R.s.) - physcion (2.96 mg/g R.j.C; 1.23 mg/g R.j.P; 1.86 mg/g Rxb; 0.19 mg/g R.s.)	[ ]
Root, stalk and leaves extract of F. japonica (Houtt) (F.j.) and F. sachalinensis (F. Schmidt)(F.s.)	LC-MS-Q/TOF isocratic mode UPLC-PDA gradient mode	methanol-acetonitrile (15:85 v/v) 0.25% aqueous acetic acid (solvent A) acetonitrile (solvent B)	- flavan-3-ols (leaves: 0.04–0.26 g/100 g F.j.; 0.04–0.23 g/100 g F.s.; stalk: 0.01–0.18 g/100 g F.j.; 0.02–0.24 g/100 g F.s.; roots: 0.02–1.48 g/100 g F.j.; 0.07–0.62 g/100 g F.s.) - phenolic acids (leaves: 0.01–0.49 g/100 g F.j.; 0.01–0.58 g/100 g F.s.; stalk: 0.01–0.08 g/100 g F.j.; 0.01–0.07 g/100 g F.s.; roots: 0.0–0.01 g/100 g F.j.; 0.0–0.03 g/100 g F.s.) - flavones/flavonols: (leaves: 0.01–1.71 g/100 g F.j.; 0.01–0.89 g/100 g F.s.; stalk: 0.01–0.28 g/100 g F.j.; 0.01–0.16 g/100 g F.s.; roots: 0.01 g/100 g F.j.; 0.01 g/100 g F.s.) - stilbenes: (leaves: 0.01–0.03 g/100 g F.j.; 0.01–0.02 g/100 g F.s.; stalk: 0.01–0.04 g/100 g F.j.; 0.01–0.06 g/100 g F.s.; roots: 0.02–0.50 g/100 g F.j.; 0.02–0.22 g/100 g F.s.)	[ ]
Rhizome extracts of R. japonica, R. sachalinensis and R. x bohemica	LC-ESI-MS/MS gradient mode	water-formic acid (99.9:0.1) (solvent A) acetonitrile-formic acid (99.9:0.1) (solvent B)	- procyanidins with high degree of polymerization; dianthrone glycosides; phenylpropanoid disaccharide esters; hydroxycinnamic acid derivatives; lignin oligomers; izovitexin; izovitexin diglucoside	[ ]
Leaves extract of F. japonica (F.j.) and F. x bohemica (Fxb)	HPTLC–MS/MS	developing agent: 0.1% TBHQ in methanol: acetone (1:1, v/v)	- violaxanthin: green leaves (4.9–53.3 mg/100 g F.j.; 3.9–39.9 mg/100 g Fxb), yellow leaves (<LOQ F.j.; 1.5 mg/100 g Fxb), green-yellowish leaves (4.2 mg/100 g F.j.; 7.1–96.8 mg/100 g Fxb) - neoxanthin: green leaves (38.2 mg/100 g F.j.; 24.4 mg/100 g Fxb), yellow leaves (<LOQ F.j. and Fxb), green-yellowish leaves (3.3 mg/100 g F.j.; 44.3 mg/100 g Fxb) - luteoxanthin: green leaves (2.9–6.3 mg/100 g F.j.; 2.2–5.4 mg/100 g Fxb), yellow leaves (<LOQ F.j. and Fxb), green-yellowish leaves (1.1 mg/100 g F.j.; <LOQ Fxb) - antheraxanthin: green leaves (10.3 mg/100 g F.j.; 12.8 mg/100 g Fxb), yellow leaves (1.0 mg/100 g F.j.; 2.0 mg/100 g Fxb), green-yellowish leaves (6.4 mg/100 g F.j.; 3.6 mg/100 g Fxb) - all-trans-lutein: green leaves (144.3 mg/100 g F.j.; 97.1 mg/100 g Fxb), yellow leaves (9.4 mg/100 g F.j.; 28.6 mg/100 g Fxb), green-yellowish leaves (55.8 mg/100 g F.j.; 127.9 mg/100 g Fxb) - all-trans-zeaxanthin: green leaves (3.4 mg/100 g F.j.; 2.7 mg/100 g Fxb), yellow leaves (1.8 mg/100 g F.j.; 6.1 mg/100 g Fxb), green-yellowish leaves (5.1 mg/100 g F.j.; <LOQ Fxb) - 13-cis-β-carotene: green leaves (1.4 mg/100 g F.j.; 0.9 mg/100 g Fxb), yellow leaves (<LOQ F.j. and Fxb), green-yellowish leaves (<LOQ F.j.; 1.9 mg/100 g Fxb) - all-trans-β-carotene: green leaves (97.3 mg/100 g F.j.; 68.7 mg/100 g Fxb), yellow leaves (8.0 mg/100 g F.j.; 12.7 mg/100 g Fxb), green-yellowish leaves (23.2 mg/100 g F.j.; 97.4 mg/100 g Fxb) - 9-cis-β-carotene: green leaves (8.6 mg/100 g F.j.; 6.1 mg/100 g Fxb), yellow leaves (<LOQ F.j. and Fxb), green-yellowish leaves (<LOQ F.j.; 9.8 mg/100 g Fxb) - other 8 carotenoid esters	[ ]
Root, Stem, Leaf and Flower extract of F. japonaica (F.j.) and F x bohemica (Fxb)	UPLC gradient mode	methanol (solvent A) water (solvent B)	- polydatin (root: 5.72–13.38 mg/g F.j.; 0.43–13.68 mg/g Fxb; stem: 0.08–0.11 mg/g F.j.; 0.01–0.1 mg/g Fxb; stem and leaf: 0.16–0.3 mg/g F.j.; 0.2–0.28 mg/g Fxb; leaf: 0.13–0.25 mg/g F.j.; 0.05–0.41 mg/g Fxb; flowers: ND) - resveratrol (root: 0.83–12.07 mg/g F.j.; 0.05–2.74 mg/g Fxb; stem: ND; stem and leaf: 0.03–0.15 mg/g F.j.; 0.03–0.05 mg/g Fxb; leaf: ND; flowers: ND) - emodin (root: 0.55–13.38 mg/g F.j.; 0.0–5.42 mg/g Fxb; stem: 0.0–0.06 mg/g F.j.; 0.0–0.05 mg/g Fxb; stem and leaf: 0.06–0.41 mg/g F.j.; 0.11–0.12 mg/g Fxb; leaf: 0.0–0.05 mg/g F.j.; 0.0–0.05 mg/g Fxb; flowers: ND) - physcion (root: 3.97–15.72 mg/g F.j.; 0.0–9.71 mg/g Fxb; stem: 0.0–0.33 mg/g F.j.; 0.0–0.07 mg/g Fxb; stem and leaf: 0.16–0.77 mg/g F.j.; 0.24–0.39 mg/g Fxb; leaf: 0.0–0.89 mg/g F.j.; 0.0–0.06 mg/g Fxb; flowers: ND)	[ ]
Root extract of P. cuspidatum Sieb. et Zucc.	HSCCC gradient mode	light petroleum-ethyl acetate-water (1:5:5, v/v) light petroleum-ethyl acetate-methanol-water (3:5:4:6, v/v) light petroleum-ethyl acetate-methanol-water (3:5:7:3, v/v)	- piceid (19.3 mg), anthraglycoside B (17.6 mg) from 200 mg sample - resveratrol (18.5 mg), emodin (35.3 mg) and physcion (8.2 mg) from 220 mg sample	[ ]
Sprout extract of R. japonica (R.j.) R. sachalinensis (R.s.) and Bohemian knotweed (B.k.)	HPLC-DAD gradient mode	water-acetonitrile-orthophosphoric acid (94.9:5:0.1 v/v)(solvent A) water-acetonitrile-orthophosphoric acid (80:19.9:0.1 v/v)(solvent B)	- catechin (103 mg/kg R.j.; 167 mg/kg R.s.; 42 mg/kg B.k.) - epicatechin (568 mg/kg R.j.; 674 mg/kg R.s.; 230 mg/kg B.k.) - resveratroloside (48 mg/kg R.j.; 31 mg/kg R.s.; 11 mg/kg B.k.) - piceid (683 mg/kg R.j.; 502 mg/kg R.s.; 215 mg.kg B.k.) - resveratrol (64 mg/kg R.j.; 29 mg/kg R.s.; 23 mg/kg B.k.)	[ ]
Root extract of P. cuspidatum Sieb. et Zucc.	HPLC-DAD and HPLC-ESI/MS gradient mode	water:acetic acid (95.5:0.5)(solvent A) acetonitrile (solvent B)	- piceid (1.75–5.03 mg/g) - resveratrol (0.378–1.15 mg/g) - emodin-8-β-D-glucoside (3.69–9.60 mg/g) - physcion-8-β-D-glucoside (0.299–0.854 mg/g) - aloe-emodin (0.032–0.109 mg/g) - emodin (1.05–2.50 mg/g) - physcion (0.180–0.456 mg/g)	[ ]
Leaves extract of F. japonica Houtt (F.j.), F. sachalinensis F. Schmidt (F.s.) and F. x bohemica (Fxb)	HPTLC–MS/MS	developing agent: acetonitrile	- flavan-3-ols monomers: total content 84 mg/100 g F.j.; 236 mg/100 g F.s.; 139 mg/100 g Fxb - proanthocyanidin dimers: total content 99 mg/100 g F.j.; 206 mg/100 g F.s.; 140 mg/100 g Fxb	[ ]
Roots extracts of R. japonica	UHPLC-DAD- ESI-MS gradient mode	water-formic acid (99.9:0.1) (solvent A) acetonitrile-formic acid (99.9:0.1) (solvent B)	- 4 stilbene (glycosides and aglycones) total amount of different extraction methods: 55.45 mg/g plant - 8 anthranoids (glycosides and aglycones) total amount of different extraction methods: 14.91 mg/g plant	[ ]

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Cucu, A.-A.; Baci, G.-M.; Dezsi, Ş.; Nap, M.-E.; Beteg, F.I.; Bonta, V.; Bobiş, O.; Caprio, E.; Dezmirean, D.S. New Approaches on Japanese Knotweed ( Fallopia japonica ) Bioactive Compounds and Their Potential of Pharmacological and Beekeeping Activities: Challenges and Future Directions. Plants 2021 , 10 , 2621. https://doi.org/10.3390/plants10122621

Cucu A-A, Baci G-M, Dezsi Ş, Nap M-E, Beteg FI, Bonta V, Bobiş O, Caprio E, Dezmirean DS. New Approaches on Japanese Knotweed ( Fallopia japonica ) Bioactive Compounds and Their Potential of Pharmacological and Beekeeping Activities: Challenges and Future Directions. Plants . 2021; 10(12):2621. https://doi.org/10.3390/plants10122621

Cucu, Alexandra-Antonia, Gabriela-Maria Baci, Ştefan Dezsi, Mircea-Emil Nap, Florin Ioan Beteg, Victoriţa Bonta, Otilia Bobiş, Emilio Caprio, and Daniel Severus Dezmirean. 2021. "New Approaches on Japanese Knotweed ( Fallopia japonica ) Bioactive Compounds and Their Potential of Pharmacological and Beekeeping Activities: Challenges and Future Directions" Plants 10, no. 12: 2621. https://doi.org/10.3390/plants10122621

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Japanese Knotweed (with Resveratrol)

Japanese knotweed is an herbaceous perennial plant native to Japan and China that grows persistently across the world. It is a potent source of resveratrol and other phytochemicals that offer powerful medicinal benefits.

Benefits of Japanese Knotweed

Cardiovascular Health Support

Immune system boost, anti-infammatory properties, quick facts, what is japanese knotweed.

A good word to describe Japanese knotweed is tenacious . Native to Japan and China, it was carried to Great Britain for use as an ornamental garden plant. From there, it was brought to Canada, the United States, and New Zealand, where it is now considered a rapidly expanding invasive.

Japanese knotweed is an attractive plant that looks like bamboo but with broad leaves. Once planted, the rhizome (root) expands rapidly, pushing out any other plants in the vicinity.

white japanese knotweed flowers growing between large green leaves

While horticulturists have declared war on this invasive, herbalists are celebrating . Those tenacious rhizomes contain potent bioactive substances like trans-resveratrol, an active form of resveratrol (an age-defying and life-enhancing compound) that is best absorbed and utilized by the body.

Beyond resveratrol, Japanese knotweed contains a wide spectrum of chemical compounds offering impressive benefits. Together, these substances offer antimicrobial activity, immune balance, cardiovascular support, antioxidant and anti-inflammatory benefits, liver protection, and nerve protection.

Benefits of Japanese Knotweed and How It Works

Source of resveratrol.

Resveratrol is a natural antioxidant found in red wine, grapes, and the roots of Japanese knotweed. Modern research has shown this compound to contain strong anti-inflammatory and antioxidant activity, as well as properties that offer protection to the cardiovascular system and immune system. 1

Trans-resveratrol is the chemical form of resveratrol best absorbed and utilized by the body . While red grapes are high in resveratrol, it must be converted into trans-resveratrol in the body. Japanese knotweed contains mostly trans-resveratrol, making it a preferred source of the compound .

Antimicrobial Support

Japanese knotweed is a systemic antimicrobial providing activity against a wide range of bacteria, viruses, protozoa, and yeast. Japanese knotweed contains phytochemical constituents that are known to pass across the blood-brain barrier, raising interesting therapeutic possibilities for brain health and the imbalances of the brain microbiome .

Recent in vitro research out of John Hopkins University (JHU) supports the anecdotal findings of the clinical use of Japanese knotweed for combating tick-borne diseases .

A 2020 JHU study found Japanese knotweed to be highly active against Borrelia burgdorferi , a bacteria that causes Lyme disease. 2 While another study published in 2021 demonstrated the herb’s ability to inhibit Babesia duncani , a parasite acquired from ticks that sometimes presents as a coinfection alongside Lyme disease. 3

Beyond this impressive emerging research on tick-borne diseases, many other studies also demonstrate Japanese knotweed’s ability to fight various microbes .

A 2013 in vitro study showed that Japanese knotweed can inhibit Aspergillus fumigatus , a mold that can cause allergic reactions and respiratory illness, as well as Staphylococcus aureus , a staph bacteria that is normally harmless but under the right conditions can cause an antibiotic-resistant infection. 4

Emodin and resveratrol are two of the phytochemicals found in Japanese knotweed roots that have antiviral activity . These bioactive compounds have shown in vitro activity against Epstein-Barr virus (EBV), SARS-CoV-2, human immunodeficiency virus type 1 (HIV-1), and more. 5

Immune Balance

Japanese knotweed is recognized as an immunomodulator, meaning it can calm overactive portions of the immune system while also boosting immunity against pathogens. It is especially useful for balancing immune system functions disrupted by chronic stress and microbes .

In a 2015 animal study, healthy mice were given a Japanese knotweed extract for three weeks to assess its effects on the immune system. The researchers found that the Japanese knotweed extract stimulated immune cells and enhanced immune functions like phagocytosis, a cellular process that can help destroy harmful microbes. 6

close up of white japanese knotweed flowers growing on stem

Cardiovascular Support

Resveratrol offers significant cardiovascular benefits , including support for optimal heart function, enhanced blood flow via dilation of blood vessels, enhanced integrity of blood vessel walls, and reduced blood viscosity (thickness).

In a 2014 randomized human clinical trial, a combination of Japanese knotweed extract and hawthorn extract was found to inhibit atherosclerosis as effectively as a statin medication . The authors suggested this effect was due to the herb’s anti-inflammatory actions and ability to reduce tissue damage. 7

Anti-Inflammatory and Antioxidant Activity

Japanese knotweed possesses potent antioxidant and anti-inflammatory properties that protect the brain, gastrointestinal tract, nervous system, and liver.

In a 2020 animal study, Japanese knotweed extract demonstrated its ability to protect stomach lining and reduce stomach ulcers through its anti-inflammatory and antioxidant activity. 8

Japanese knotweed can also be helpful in counteracting the inflammation and oxidative stress that can sometimes accompany physical exercise .

In a 2013 double-blind, placebo-controlled human clinical trial, researchers gave 20 healthy male professional basketball players 200 mg of Japanese knotweed extract standardized to 20% trans-resveratrol daily for six weeks.

After six weeks, inflammatory markers were significantly reduced in those taking the supplement , while those taking the placebo had no observable change. A suggested mechanism of action was the inhibition of pro-inflammatory pathways like NF-κB. 1

Brain Health

Japanese knotweed and its key phytochemical resveratrol offer a wide range of benefits to the brain .

Resveratrol can help balance the HPA axis (a complex feedback system that regulates the body’s reaction to stress), reduce inflammation and oxidative stress in the brain, enhance the growth of new nerve tissue, and increase neurotransmitter production . 9

These mechanisms can help to improve mood and cognitive functions, protect the brain from excessive aging, and more.

Resveratrol can also increase brain-derived neurotrophic factor (BDNF), a protein that plays a pivotal role in neuroplasticity and overall brain health .

A 2015 animal study assessed the effect resveratrol had on decreased BDNF and depressive-like behaviors due to stress. The study found that resveratrol mitigated these effects by regulating the HPA axis and increasing brain levels of BDNF. 10

Additionally, in vitro studies show that resveratrol can reduce amyloid beta, the primary component of plaques found in the brains of Alzheimer’s patients. 9 While the jury is still out on the exact role of amyloid beta buildup in the progression of Alzheimer’s, Japanese knotweed may be an important herb to keep an eye on.

History & Traditional Use

Japanese knotweed has an extensive history of traditional use in both China and Japan for infections, inflammation, liver issues, and skin issues. 11

The root is listed in the Chinese Pharmacopoeia , an official compilation of traditional Chinese and western medicines. In traditional Chinese medicine, the root is used to support the liver, promote blood circulation, and support the respiratory system. 12

Chinese herbal medicine knotweed stalk close-up

Japanese knotweed is also used as a food in many Asian countries, often being compared to asparagus or rhubarb. In China and Japan, the young shoots are harvested and preserved in salt or cooked fresh.

Additionally, Japanese knotweed is prepared and consumed as a tea in China and Japan. This form of preparation is known as itadori , a Japanese word that translates to “removes pain”. 13

How to Use and Dosing

The general suggested dosage for a Japanese knotweed powdered extract is 200-800 mg ( standardized to 50% trans-resveratrol) two to three times daily .

If using a tincture, general dosing is 1-2 mL up to three times daily.

For added cardiovascular support, Japanese knotweed can be combined with other herbs like hawthorn , garlic , ginkgo , gotu kola , and reishi mushroom .

To support immune function and balance the microbiome, Japanese knotweed combines well with andrographis , berberine , cat’s claw , Chinese skullcap , and garlic .

Interactions

Caution is advised if also taking anticoagulant medications because resveratrol has blood-thinning properties.

Always check with your health care practitioner before use if you are taking medications. For more general education on potential interactions between herbs and medications, check out Dr. Bill Rawls’ article: Is it Safe to Take Herbs with My Medications?

Precautions & Side effects

Side effects are rare, with a low potential for toxicity. Japanese knotweed has been used in traditional forms of Asian medicine for thousands of years and offers a high level of safety. Check with your health care provider before using Japanese knotweed if you are pregnant or nursing.

Disclaimer: This information is intended only as general education and should not be substituted for professional medical advice. Any mentioned general dosage options, safety notices, or possible interactions with prescription drugs are for educational purposes only and must be considered in the context of each individual’s health situation and the quality and potency of the product being used. Use this information only as a reference in conjunction with the guidance of a qualified healthcare practitioner.

Want to See the Science? Check Out Our References Below.

1. Zahedi HS, Jazayeri S, Ghiasvand R, Djalali M, Eshraghian MR. Effects of polygonum cuspidatum containing resveratrol on inflammation in male professional basketball players. Int J Prev Med . 2013;4(Suppl 1):S1-S4. 2. Feng J, Leone J, Schweig S, Zhang Y. Evaluation of Natural and Botanical Medicines for Activity Against Growing and Non-growing Forms of B. burgdorferi. Front Med (Lausanne). 2020;7:6. Published 2020 Feb 21. doi:10.3389/fmed.2020.00006 3. Zhang Y, Alvarez-Manzo H, Leone J, Schweig S, Zhang Y. Botanical Medicines Cryptolepis sanguinolenta, Artemisia annua, Scutellaria baicalensis, Polygonum cuspidatum, and Alchornea cordifolia Demonstrate Inhibitory Activity Against Babesia duncani. Front Cell Infect Microbiol . 2021;11:624745. Published 2021 Mar 8. doi:10.3389/fcimb.2021.624745 4. Zhang L, Ravipati AS, Koyyalamudi SR, et al. Anti-fungal and anti-bacterial activities of ethanol extracts of selected traditional Chinese medicinal herbs. Asian Pac J Trop Med . 2013;6(9):673-681. doi:10.1016/S1995-7645(13)60117-0 5. Jug U, Naumoska K, Malovrh T. Japanese Knotweed Rhizome Bark Extract Inhibits Live SARS-CoV-2 In Vitro. Bioengineering (Basel) . 2022;9(9):429. Published 2022 Sep 1. doi:10.3390/bioengineering9090429 6. Chueh FS, Lin JJ, Lin JH, Weng SW, Huang YP, Chung JG. Crude extract of Polygonum cuspidatum stimulates immune responses in normal mice by increasing the percentage of Mac-3-positive cells and enhancing macrophage phagocytic activity and natural killer cell cytotoxicity. Mol Med Rep . 2015;11(1):127-132. doi:10.3892/mmr.2014.2739 7. Liu LT, Zheng GJ, Zhang WG, Guo G, Wu M. Zhongguo Zhong Yao Za Zhi . 2014;39(6):1115-1119. 8. Kim YS, Nam Y, Song J, Kim H. Gastroprotective and Healing Effects of Polygonum cuspidatum Root on Experimentally Induced Gastric Ulcers in Rats. Nutrients . 2020;12(8):2241. Published 2020 Jul 27. doi:10.3390/nu12082241 9. Moore A, Beidler J, Hong MY. Resveratrol and Depression in Animal Models: A Systematic Review of the Biological Mechanisms. Molecules . 2018;23(9):2197. Published 2018 Aug 30. doi:10.3390/molecules23092197 10. Ali SH, Madhana RM, K V A, et al. Resveratrol ameliorates depressive-like behavior in repeated corticosterone-induced depression in mice. Steroids . 2015;101:37-42. doi:10.1016/j.steroids.2015.05.010 11. Peng W, Qin R, Li X, Zhou H. Botany, phytochemistry, pharmacology, and potential application of Polygonum cuspidatum Sieb.et Zucc.: a review. J Ethnopharmacol . 2013;148(3):729-745. doi:10.1016/j.jep.2013.05.007 12. Zhang H, Li C, Kwok ST, Zhang QW, Chan SW. A Review of the Pharmacological Effects of the Dried Root of Polygonum cuspidatum (Hu Zhang) and Its Constituents. Evid Based Complement Alternat Med . 2013;2013:208349. doi:10.1155/2013/208349 13. Burns J, Yokota T, Ashihara H, Lean ME, Crozier A. Plant foods and herbal sources of resveratrol. J Agric Food Chem . 2002;50(11):3337-3340. doi:10.1021/jf0112973 14. Rege SD, Geetha T, Griffin GD, Broderick TL, Babu JR. Neuroprotective effects of resveratrol in Alzheimer disease pathology. Front Aging Neurosci . 2014;6:218. Published 2014 Sep 11. doi:10.3389/fnagi.2014.00218 15. Guan SY, Zhang K, Wang XS, et al. Anxiolytic effects of polydatin through the blockade of neuroinflammation in a chronic pain mouse model. Mol Pain . 2020;16:1744806919900717. doi:10.1177/1744806919900717 16. Ghanim H, Sia CL, Abuaysheh S, et al. An antiinflammatory and reactive oxygen species suppressive effects of an extract of Polygonum cuspidatum containing resveratrol. J Clin Endocrinol Metab . 2010;95(9):E1-E8. doi:10.1210/jc.2010-0482 17. Ma X, Leone J, Schweig S, Zhang Y. Botanical Medicines With Activity Against Stationary Phase Bartonella henselae. Infectious Microbes and Diseases . 2021;3(3):158-167. doi:10.1097/im9.0000000000000069

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New Penn State resource for spring weed control in grass hay and pastures
Lesser celandine: Spring garden and lawn invader
Bindweeds: field and hedge bindweed
Spreading Dogbane
Common corncockle
New Tool: Identifying spring rosettes
Waterhemp found in Jefferson County
Creeping Buttercup in Corn

Japanese Knotweed

Japanese Knotweed ( Reynoutria japonica ) is an invasive weed that is problematic in perennial agricultural systems such as berry crops and tree fruit. It is also found on landscapes, sodded storm drains, river banks, roadsides, waste areas and untended gardens. This weed tends to thrive on moist, well-drained, nutrient rich soil and is present throughout the Northeast. Japanese knotweed and the related giant, Bohemian, and Himalayan knotweeds are fast-growing and form dense stands, allowing little to no other vegetation to survive. It is semi-shade tolerant, but is most aggressive in full sun.

Japanese knotweed infestation

Photo by Leslie J. Mehrhoff of the University of Connecticut, via Bugwood.org

Identification

Seedlings : Seedlings are rarely encountered. Most new plants arise from stem or root fragments; early growth will be young reddish shoots emerging from the plant fragment.

Japanese knotweed emerging from roots

Mature plant : Knotweed stems are hollow, stout, and green to purple, with prominent joints where leaves emerge from the stem. Leaves alternate, 8-15 cm long and 5-10 cm wide (3-6″ long by 2-4″ wide), and are broadly egg-shaped with a flat base and pointed tip. The root system is extensive, with a large root ball and underground root runners (rhizomes). This plant spreads mainly by these spreading rhizomes and stem fragments; any piece of the plant with a root or stem joint can start a new plant.

Thicket of Japanese knotweed stems

Photo by Barbara Tokarska-Guzik of the University of Silesia, Poland, via Bugwood.org

Japanese knotweed root structure

Photo by John Cardina of OSU, via Bugwood.org

Flowers/Fruit: Knotweed produces a showy spray of numerous, small white flowers, which bloom on elongated clusters in late summer. The plant is insect-pollinated and is often frequented by honeybees. Seeds are 3mm (1/10”), dark brown, triangular, and enclosed within a 3-winged papery husk (calyx).

Similar large knotweed species: giant knotweed on the left, bohemian knotweed in the center, and Japanese knotweed on the right.

Photo by Barbara Tokarska-Guzlik of the University of Silesia, Poland, via Bugwood.org.

Japanese knotweed stems, showing purple mottling.

Photo by Joseph M. DiTomaso of UC-Davis, via Bugwood.org.

Japanese knotweed stems are hollow and chambered.

Photo by Leslie J. Mehrhoff of the University of Conncicut, via Bugwood.org.

Japanese knotweed stems from previous year, with new spring growth.

Photo by Jan Samanek of the Phytosanitary Administration, via Bugwood.org.

Chemical control

The best management practice for Japanese knotweed is a combination of mechanical and chemical control. Mowing or cutting in June with all downed plant material collected and destroyed, followed by glyphosate or triclopyr applications in late summer provides the best control. This is a multi-year endeavor, with repeat applications for several years. Glyphosate-treated knotweed can have epinastic or stunted regrowth, which makes reapplication the following year ineffictive. In this situation, waiting until the second year after treatment allows the plant to produce enough aboveground material for an effective reapplication.

The University of Michigan has produces an excellent publication that details the biology and management of knotweed.

Cornell University’s Turf and Landscape weed identification app provides New York State specific options for chemical management of Japanese knotweed.

Use this tool to look up the efficacy of herbicides on a particular weed species. For general guidance on weed control, get the latest edition of the Cornell Crop and Pest Management Guidelines .

Non-chemical control

For Japanese knotweed, the size of infestation is even more important than normal for selecting a control method. Very small infestations of a few stems can be controlled by carefully digging out the plant and all of the root system, but the site must be monitored for several years and any remaining regrowth dug out as well. Generally a site can be considered managed after no knotweed regrowth is observed for three years. All plant fragments must be removed and destroyed to prevent them from starting new infestations.

Larger infestations are much more difficult to manage without a chemicals. Knotweed’s underground root system is extensive and stores enough energy to regrow for several years. It is worth considering the combination of mechanical and chemical management described to the right, as management without chemicals is difficult and requires many years of continuous effort.

If non-chemical management is the only option, smothering may be the best approach. Cut all knotweed stems in early June, cover them with mulch such as grass clippings, and cover the entire area and a wide buffer around it with a thick, opaque plastic tarp. The buffer is necessary to prevent new growth from the plant’s extensive rhizome (underground runner) system. This tarp is left in place for five years, and must be patched or replaced to maintain continuous cover of the entire plant system.

There is one biocontrol insect for Japanese knotweed under study in New York; research release trials started in 2020 under the direction of the Blossey Lab at Cornell University. This insect is not available to the public yet, and there are no other biocontrols available for knotweed .

See A Grower’s Guide to Organic Apples from Cornell for non-chemical weed control options in apple orchards.

Uva R H, Neal J C, DiTomaso J M. 1997. Weeds of the Northeast . Book published by Cornell University, Ithaca NY. The go-to for weed ID in the Northeast; look for a new edition sometime in 2019.

Cornell University’s Turfgrass and Landscape Weed ID app . Identification and control options for weeds common to turf, agriculture, and gardens in New York; uses a very simple decision tree to identify your weed.

Michigan Department of Natural Resources, Michigan Natural Features Inventory, 2012. Invasive Species—Best Control Practices: Japanese Knotweed. This is an excellent treatment of Japanese knotweed identification, biology, and management.

Northwoods Cooperative Weed Management Area: Homeowner’s Guide to Japanese Knotweed Control . 2007.

Profile on Japanese Knotweed by Michigan Department of Natural Resources including extensive descriptions on management.

Profile on Japanese Knotweed from the Weed Report from the Weed Control in Naturala Areas in the Western United States , shared by University of California, Davis.

All images are included from Invasive.org . Offers an extensive online library of images for invasive and exotic species of North America.

Peck, G M and I A Merwin. A Grower’s Guide to Organic Apples . Covers organic weed control methods for organic apple orchards.

Breth, D I and E Tee. 2016. Herbicide AI by Weed Species . This tool allows you to look up the efficacy of an herbicide active ingredient on a particular weed species.

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Introduction

Physical description

History of invasion.

What are angiosperms?
How are angiosperms different than gymnosperms?
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Macro image of pollen-covered bee on purple crocus. (flowers, stamen, pollination, insects, nature)

Japanese knotweed

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Table Of Contents

Japanese knotweed , ( Fallopia japonica ), herbaceous perennial plant of the buckwheat family ( Polygonaceae ) native to China , Korea , and Japan . Persistent and aggressive, Japanese knotweed is a noxious weed in many areas outside its native range and ranks among the world’s worst invasive species .

Japanese knotweed is a tall dense shrub that can rapidly grow to a height of 3–4.5 meters (10–15 feet). Arising in the spring from spreading underground rhizomes and a deep taproot , the hollow jointed stems are reminiscent of bamboo and assume an orange hue when mature. The simple ovate leaves are borne alternately along the stems and reach up to 15 cm (6 inches) in length. The leaves emerge red-purple in color and eventually fade to green. In late summer showy clusters of small white or light green flowers appear along the stems. The small winged fruits produce tiny triangular seeds that are readily dispersed by wind and water. The plant dies back to its rhizomes in the fall.

Japanese knotweed thrives in areas with disturbed soil , such as farmsteads, trails, and roadsides, where the conditions are prime for seed germination and for the spread of the plant’s rhizomes. The plant can tolerate drought, full sun, deep shade, high temperatures, and high soil salinity and is frequently found along streams and rivers. Japanese knotweed is allelopathic, meaning it releases chemicals into the soil that inhibit the survival of surrounding plants. Its rapid growth, easy sexual and asexual proliferation, and chemical edge are all traits that give the plant considerable competitive advantage among plants that did not evolve to withstand its encroachment—such as those in Europe and North America—and allow it to form vast monospecies stands.

Japanese knotweed was first taken to Europe from East Asia in the mid-18th century for use in landscaping. Gardeners appreciated the plant for its quick, reliable growth, and it gained popularity, though it soon spread beyond the boundaries of the gardens and parks where it had been planted. In the 1870s the plant was brought to North America as an ornamental and privacy hedge and to control erosion . Japanese knotweed quickly escaped cultivation in the eastern United States , and its spread spiraled out of control in both Europe and North America.

As of 2019 Japanese knotweed was present in 42 U.S. states and 8 Canadian provinces. The plant is also considered invasive in much of Europe, where it has entangled the Balkan Peninsula and Italy , Portugal , and Spain , among other countries. The United Kingdom’s Environment Agency has named Japanese knotweed the country’s most invasive and destructive plant. Despite determined efforts to eliminate it, Japanese knotweed has proven to be a persistent threat to ecosystem balance, successfully outcompeting many native plants and forming dense thickets that do little to support local wildlife.

Japanese knotweed is notoriously difficult to eliminate. Foliar herbicides are typically not sufficient to kill its extensive root and rhizome network. Arduously digging out the rhizomes usually proves impractical and unrealistic, as the plant can regrow from even a miniscule fragment that remains in the soil. Such soil disturbance also churns the soil seed bank , promoting the germination of a new generation of Japanese knotweed seeds. Management thus often focuses on reducing the plants’ size in a slow and tenacious fight, rather than attempting to eliminate them quickly. Land managers chop off the stalks of established plants and may coat new sprouts in herbicides containing glyphosate or triclopyr. Cut stalks are then often painstakingly collected to limit new clones from sprouted stem fragments. Cutting the plants down at least three times a year prevents them from going to seed, and, more importantly, limits the amount of nutrition moving from the leaves to the persistent rhizomes. After several years, the rhizomes may become too depleted to regenerate in the spring, and the stand will eventually be brought under control.

The Status of Herbicide Resistant Weeds in Turfgrass Systems

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By Tripp Rogers and Travis Gannon

Herbicide-resistant weeds are a leading problem in the turfgrass industry and may compromise the functionality and aesthetic quality of turfgrass systems.

What is herbicide resistance? Herbicide-resistant weeds are not a new problem in turfgrass systems (or any agricultural system). Herbicide resistance is a selection process that develops through the repeated use of the same herbicide or herbicides with the same mechanism of action (MOA). Typically, herbicide resistance traits are present within a population at very low levels and the continuous application of the same herbicide (or herbicide with same MOA) over time removes susceptible plants allowing resistant individuals to survive, grow, reproduce, and proliferate.

What has contributed to herbicide resistance in turfgrass systems? There are a number of factors that contributed; however, overreliance on herbicides over time is a primary contributor coupled with not rotating MOAs. It’s also important to note, herbicides with new and novel MOAs have been very limited in recent years (which limits turfgrass managers ability to rotate MOAs), particularly in certain turfgrass species and/or systems.

What should turfgrass managers do to mitigate or delay resistance?

1. Promote a healthy, thick turfgrass sward. Common methods for promoting healthy turfgrass systems include selecting an adapted turfgrass species, scouting for disease activity, proper fertilization and irrigation as well as ensuring that stands are mowed at the appropriate height and frequency. 2. Implement integrated weed management (IWM) strategies. It’s important to employ various integrated (preventative, mechanical, chemical, cultural, etc.) weed management techniques and not rely solely on herbicides. 3. When using herbicides, rotate MOAs. Less expensive herbicides may be effective initially, but overreliance on these products significantly increases the likelihood of resistance (and greater associated costs) in the long-term. Refer to this for a complete list of herbicides and respective MOAs. 4. Use multiple MOAs with PRE and POST activity within a season. An example of this for annual bluegrass in non-overseeded bermudagrass is using a PRE herbicide (examples include indaziflam, prodiamine, pendimethalin, simazine, among others) at optimum PRE timing for your location with a POST herbicide (examples include foramsulfuron, flazasulfuron, rimsulfuron, sulfosulfuron, trifloxysulfuron, among others) applied POST. Turfgrass managers can also delay the initial application and combine PRE and POST herbicides into a single application (tank-mix). When feasible (non-overseeded, dormant bermudagrass), well-timed applications of a non-selective herbicide such as glyphosate or glufosinate may also enhance efficacy while including an additional MOA. It’s also important to note POST herbicides should be applied to small, actively growing weeds to obtain optimal control. 5. Use the appropriate herbicide rate to maximize efficacy (and minimize escapes). Sub-lethal herbicide rates may expedite resistance evolution. 6. Ensure environmental and edaphic (soil) conditions are optimal. Conditions should be monitored prior to, at, and following application.

Identification of resistant populations. Herbicide resistance must be confirmed through a comparison of resistant and susceptible plants in a replicated scientific trial, which may not be practical for professional turfgrass managers to complete themselves. There are several university laboratories that can confirm if your weed is resistant to a given herbicide or MOA.

What resulted in failed or reduced efficacy (if I don’t have resistance)? Just because you did not obtain control after an application does not confirm herbicide resistance as there are multiple reasons why an herbicide application may not have been efficacious. A partial checklist:

Was the herbicide applied at the correct time? This is especially important for preemergent (PRE) herbicide applications. PRE herbicides should be applied based on environmental conditions (i.e. soil temperature and moisture content), not calendar dates.

Were environmental conditions conducive for efficacy? If foliar-absorbed postemergent (POST) herbicides are applied in winter and plants are not actively growing at application, the herbicide may not have been adequately absorbed and / or translocated.

Was there a rainfall or irrigation event that potentially moved the herbicide? Herbicides have varying rates of aqueous solubility that affect sorption to soil and organic matter. While PRE herbicides need irrigation or rainfall, if a product is highly water soluble and has low binding affinity, excessive rainfall or irrigation may move the herbicide off-target, potentially compromising efficacy.

Was the herbicide applied to a saturated soil or did the soil become saturated after application? In anaerobic soils (saturated), some herbicides may break down much faster than in aerobic conditions.

If you rule out the aforementioned factors that could influence herbicide efficacy, it’s time to ask a few more questions. Has the herbicide historically controlled the target weed at this location? Has control declined after years of continuous use? Are dying plants intermingled with unaffected plants in the treated area? Are other weed species in the treated area that are controlled? If you answered yes, resistance may be present and it’s likely worth additional investigation.

What can turfgrass managers do if resistance is confirmed? If an herbicide-resistant biotype is identified, it is important to act quickly. If left unchecked, a resistant population can further contribute to the soil seed bank. This means you could be dealing with resistance issues to that MOA (at this site) for the next 7-10 years, depending on multiple factors including species and seed bank dynamics. If practical, switching to an herbicide with a different efficacious MOA is the easiest way to manage a resistant biotype. If switching MOAs is not a viable option, other control means including hand removal, mechanical, cultural controls, or renovation may be required.

In summary, herbicide-resistant weeds are present in turfgrass systems and will likely become more problematic in the future. To mitigate the potential for resistance development, professional turfgrass managers are encouraged to maintain a healthy turfgrass sward, employ various aspects of integrated weed management, and rotate herbicides with differing MOAs frequently as well as use multiple MOAs within each season (when practical).

Tripp Rogers is a Ph.D. candidate under the direction of Dr. Travis Gannon in the Department of Crop and Soil Sciences at North Carolina State University.

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Steadying the hands of time

BY TROY RUMMLER

THURSDAY, AUGUST 8, 2024

US-Japanese partnership approaches an atomic clock breakthrough

All clocks are ticking down to an argument about the time. Imperceptibly, they gain or lose fractions of a second. Gradually, they drift apart until someone reads the time aloud, and somebody with a different clock begs to differ.

Unless clocks are periodically synchronized, drift is just a fact of life. Even super accurate atomic clocks experience drift. While not as much as a cheap bedroom alarm clock, it is still enough to catch the attention of Dan Thrasher, a scientist at Sandia, who believes he can create a better one.

Dan is working with Japanese tech company Nichia Corporation to build the world’s most accurate compact atomic clock. These clocks, currently about the size of a matchbook, are used in a variety of technologies from backpack radios, GPS receivers, underwater sensors, power grids and satellites. Any drift they experience limits the time these technologies can run on their own without help from a reference clock.

His project is supported by the Defense Advanced Research Projects Agency, or DARPA, through a program called H6 . The Defense Department research agency is known for funding high-tech projects with national security applications, like night vision goggles that fit like sunglasses and surveillance implants for insects.

Improving the world’s smallest atomic clock

According to Dan, scientists have been trying to do what he is doing for the past two decades since the creation of the chip-scale atomic clock, or CSAC (pronounced “sea sack”). The matchbook-sized ticker holds the title of the world’s smallest commercial atomic clock.

“What made it possible was a very small, very stable, very efficient laser,” he said.

The laser is finely tuned to just the right wavelength to tickle atoms of the element cesium, part of an intricate setup that locks in a precise timekeeping rhythm. It was first demonstrated at Sandia.

But the record-holding clock isn’t perfect.

“While a CSAC is small and important, it is still subject to sources of systematic uncertainty. The clock drifts over time,” Dan said.

Since 2008, researchers at Sandia have been working on miniaturizing a more accurate, albeit larger, type of timepiece called a microwave ion clock.

“In general, a microwave ion clock experiences less drift than a CSAC,” Dan said.

Sandia’s proposed clock would use electrically charged ions of ytterbium instead of cesium. However, no one has been able to demonstrate a small, stable and efficient ultraviolet laser required to operate it.

Partnership with Japanese company revitalizes research

Unknown to these researchers, Nichia had been making advancements in small laser technology. Its scientists successfully developed a very small, stable and efficient violet-blue laser for displaying information inside smart glasses.

The laser was the same variety used in CSACs, called a vertical cavity surface emitting laser, or VCSEL (rhymes with “pixel”). What’s more, “Nichia had been looking for a new opportunity to showcase the value of its VCSEL with violet-blue wavelength,” a Nichia spokesperson said.

Dan lit up when he read a research paper about the laser. Although its wavelength was no good for ytterbium ions, it closely matched the wavelength required for ions of another element — barium.

Barium was nobody’s first choice. As far as elements go, it is equal parts stubborn and sensitive. The last time scientists used barium to demonstrate a microwave ion clock was in 1985.

“Before I was born,” Dan said.

“There are very valid reasons to disregard barium. But we have the cat’s meow of laser technology at the right wavelength, and that alone is enough motivation for us to try to develop this,” he said.

Dan was confident he could use Nichia’s laser to build an atomic clock based on barium ions that is smaller and more accurate than the CSAC.

“There are some projects I would put my own money into. This is one of them,” he said.

He shared his idea with Nichia and DARPA.

“Nichia gladly accepted Sandia’s offer to support their study because Nichia felt this compact, low-power-consumption, single-frequency laser diode would be a key technology for the small atomic clock Sandia is targeting,” the spokesperson said.

Bumpy start gives way to successful tests

The switch to barium was not as simple as Dan had hoped. After boldly defending his proposal as low-hanging fruit, initial tests revealed that the laser deteriorated faster than expected, which meant the clock could be rendered useless after just a short time.

“That scared me,” he said.

But further studies soothed his nerves. After a longer-than-expected “burn-in” time, the rate of deterioration stabilized, indicating that the laser would stay healthy for a long time.

In June, Dan successfully used Nichia’s laser to optically detect barium ions and presented his research at the European Frequency and Time Forum in Neuchâtel, Switzerland. While this is not the same as measuring time, it demonstrates the laser possesses all the necessary qualities to operate the clock. The research itself holds potential value for certain types of quantum computing, where lasers are used to make precise measurements of trapped ions.

“This is the first time anyone has used light from a VCSEL to detect trapped ions,” he said.

Dan is enthusiastic about the future of his project.

“The light source is clearly the bottleneck in commercializing miniature microwave ion clocks. We are closer than ever before to solving this problem.”

Innovation takes time

Failure to demonstrate a light source suitable to enable a miniature microwave ion clock plagued Dan and others for years. He credits finding the path he is on now to program development funds that gave him the time to review recent relevant literature and respond to a call for proposals from a funding agency.

Although scientists and engineers are often busy and driven by deadlines, “The reason I found this resource (Nichia Corporation) was because I took the time to read the literature,” he said. “When you’re doing cutting-edge research, it’s crucial to be aware of your field and be involved in your research communities.”

It turns out scientists, like clocks, work better when they are in sync.

The mother of all motion sensors
Quantum computers’ unexpected advantage
Radar is advancing at historic speed. How engineers are setting the pace.

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Japan rivals Nissan and Honda will share EV components and AI research as they play catch up

Nissan Chief Executive Makoto Uchida, left, and Honda Chief Executive Toshihiro Mibe shake hands during a joint news conference in Tokyo, Thursday, Aug. 1, 2024. Japanese automakers Nissan and Honda say they plan to share components for electric vehicles like batteries and jointly research software for autonomous driving. (Kyodo News via AP)

FILE - Logos at a Nissan showroom are seen in Ginza shopping district in Tokyo, March 31, 2023. (AP Photo/Eugene Hoshiko, File)

FILE - Logos of Honda Motor Co. are pictured in Tsukuba, northeast of Tokyo, on Feb. 13, 2019. (Kyodo News via AP, File)

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TOKYO (AP) — Japanese automakers Nissan and Honda say they plan to share components for electric vehicles like batteries and jointly research software for autonomous driving.

A third Japanese manufacturer, Mitsubishi Motors Corp., has joined the Nissan-Honda partnership, sharing the view that speed and size are crucial in responding to dramatic changes in the auto industry centered around electrification.

A preliminary agreement between Nissan Motor Co. and Honda Motor Co. was announced in March .

After 100 days of talks, executives of the companies evinced a sense of urgency. Japanese automakers dominated the era of gasoline engines in recent decades but have fallen behind formidable new players in green cars like Tesla of the U.S. and China’s BYD.

“Companies that don’t adapt to the changes cannot survive,” said Honda Chief Executive Toshihiro Mibe. “If we try to do everything on our own, we cannot catch up.”

Nissan and Honda will use the same batteries and adopt the same specifications for motors and inverters for EV axels, they said.

By coming together in what Mibe and counterpart at Nissan, Makoto Uchida, repeatedly called “making friends” to achieve economies of scale, the companies plan more strategic investments in technology and aim to cut costs by boosting volume.

Each company will continue to produce and offer its own model offerings. But they will share resources in areas like components and software development, where “making friends” will be a plus, Mibe and Uchida told reporters.

They declined to say whether the friendship will extend to a mutual capital ownership, while noting that wasn’t ruled out.

The two companies also agreed to have their model lineups “mutually complement” each other in various global markets, including both internal combustion engine vehicles and EVs. Details on that are being worked out, the companies said.

Honda and Nissan will also work together on energy services in Japan. Under Thursday’s announcements, Mitsubishi will join as a third member.

Toyota Motor Corp. , Japan’s top automaker, is not part of the three-way collaboration.

Although Honda and Nissan have very different corporate cultures, it became clear, as their discussions on working together continued, their engineers and other workers on the ground have a lot in common, Uchida said.

“Speed is the most crucial element, considering our size,” he added.

Uchida and Mibe repeatedly stressed speed, openly admitting BYD is moving very quickly, but they said there was still time to catch up and remain in the game.

“In coming together, we will show that one plus one will add up to become more than two,” Uchida said.

Yuri Kageyama is on X: https://twitter.com/yurikageyama

Japan’s stock market is forecast to have a transformational year in 2024

The Japanese equity market is forecast by Goldman Sachs Research to rally again in 2024, boosted by solid global economic growth and stock market reform.

The TOPIX, an index of Japanese stocks, is projected to rise about 13% to 2650 by the end of 2024. Our economists expect another year of growth outperformance across most economies, including Japan’s — the country’s real (inflation adjusted) GDP growth is forecast to expand 1.5% in 2024, compared with 1% for the consensus of economist forecasts surveyed by Bloomberg.

A key part of our analysts’ forecast is the Tokyo Stock Exchange’s company governance reforms, which they say “have been a game changer for the Japanese equities market.” The stock exchange has incentivized listed companies to boost valuations and earnings, and companies could potentially be delisted if they’re unable to show they’re using their capital efficiently. Investors see the unwinding of Japanese companies’ cross-shareholdings — shares that firms own in their business partners to maintain those relationships — as an indication of improved governance.

“Continued TSE pressure on corporates to respond to its requests will lead to a further acceleration in corporate governance-related activity amongst listed Japanese companies in 2024,” Goldman Sachs Research strategists Bruce Kirk and Kazunori Tatebe write in the team’s report.

The TOPIX has soared 24% this year (as of Nov. 10) in local currency terms, its fourth-best annual performance since 2001. The Japanese benchmark has significantly outperformed the S&P500 Index of US stocks and Hong Kong’s Hang Seng Index. That said, in US dollar terms, TOPIX is still under-performing the S&P500, which could explain why dollar-based investors have been reluctant to increase their Japan weightings this year, according to Goldman Sachs Research.

Foreign investment has flowed into Japanese stocks

Investment flows from foreign funds into Japanese stocks rose sharply between April and June amid expectations for stock market reforms.

Japan’s stock market had 10 weeks of consecutive net foreign buying in cash and futures, totalling 7.9 trillion yen ($53 billion) from April to June. The stock purchases were driven by TSE-related investor interest, as well as the positive impact of Warren Buffett’s interview about Japanese equities with Nikkei Asia in April, according to Goldman Sachs Research. Foreign investors have been selling Japanese stocks in recent months (on net), but overseas flows are still positive for the year.

Foreigners and corporations are expected to remain net buyers of Japanese stocks, and domestic individual investors will become net buyers in 2024 with the new Nippon Individual Savings Account (NISA) — a program for small investments — poised to start in January.

“With Japanese households facing a sharp decline in real yields on bank deposits due to high inflation, we think the launch of the expanded `new NISA’ in January 2024 will encourage individuals to enter the stock market,” Kirk and Tatebe write. “Over the longer term, we expect households’ exposure to the stock market to remain on a steady upward trend, and that the new NISA will become an important driver.”

The economic outlook for Japan in 2024

In addition to governance reforms, Japan’s stock market has also been driven this year by the expectation that the Bank of Japan would end its ultra-loose monetary policy and by a benign currency tailwind for Japanese exporters, Kirk and Tatebe write.

Our economists expect Japan’s real GDP growth to slow to 1.5% in 2024, from 1.9% in 2023 when the economy had a tailwind from reopening from Covid restrictions. They project expansion will stay above the potential growth rate (their long-term outlook is 0.9%). Private consumption, supported by wage growth and a one-off tax refund in summer 2024, is forecast to rebound. Goods exports are predicted to gradually increase in 2024, while inbound tourist consumption will likely return to a modest recovery after the post-pandemic surge this year.

After years of chronic deflation, inflation jumped in 2023 amid immense fiscal and monetary policy actions to jumpstart the economy. Our economists forecast core CPI (which excludes fresh foods) to remain above 2% in 2024. They expect wage growth will eventually lead to a tightening in Japan’s extraordinary monetary easing and the end of the Bank of Japan’s negative interest rate policy, once policymakers have confirmed a virtuous cycle of rising wages and services prices (though there’s uncertainty about when this cycle can be confirmed).

Japanese company earnings are forecast to rise

“Japanese companies’ earnings momentum remains strong,” Kirk and Tatebe write. They forecast 12% growth in TOPIX earnings per share in 2023, 8% in fiscal year 2024, and 7% in fiscal year 2025. Growth next year is expected to be led by sectors that are recovering from cyclical downturns, such as electrical appliances, raw materials and chemicals, and machinery, as well as sectors including information and communication.

The TOPIX is predicted to rise broadly in line with the growth rate in earnings-per-share rate next year.

TSE’s continued pressure on Japanese companies, meanwhile, is part of the reason the proportion of stocks that trade below book value has declined: The share of equities in the TSE Prime market below book has fallen from 52% at the start of January to 46% now, according to Goldman Sachs Research.

And cross-shareholdings, long regarded as a core governance issue at Japanese companies, are on the decline. The unwinding of these strategic holdings has been ongoing, and there are signs this trend is gaining momentum.

“We are now seeing signs of significant changes in cross-shareholdings that were once considered untouchable,” Kirk and Tatebe write. “Investors view company announcements regarding the unwinding of cross-shareholdings as an important indication of corporate governance improvement, and as share prices often react strongly as a result, we think this theme warrants continued attention in 2024.”

This article is being provided for educational purposes only. The information contained in this article does not constitute a recommendation from any Goldman Sachs entity to the recipient, and Goldman Sachs is not providing any financial, economic, legal, investment, accounting, or tax advice through this article or to its recipient. Neither Goldman Sachs nor any of its affiliates makes any representation or warranty, express or implied, as to the accuracy or completeness of the statements or any information contained in this article and any liability therefore (including in respect of direct, indirect, or consequential loss or damage) is expressly disclaimed.

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What’s Behind All the Stock Market Drama?

Analysts and investors have many explanations, including worries about the health of the U.S. economy and shifts in the value of the Japanese yen.

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People standing at computer screens inside a stock exchange.

By Joe Rennison and Danielle Kaye

Reporting from New York

The wild swings in markets recently are a case study in how seemingly distinct pillars around the globe are connected through the financial system — and the domino effect that can follow if one of them falls.

Some of the turmoil in stocks reflected rising fear that the American labor market may be cracking , and that the U.S. Federal Reserve may have waited too long to cut interest rates .

But it’s more complicated than that. This time around, there are also more technical reasons for the sell-off, analysts and investors say. Stocks staged a modest recovery on Tuesday , but it fizzled by Wednesday afternoon, showing that the volatility has rattled investors.

Factors like a slow buildup of risky bets, the sudden undoing of a popular way to fund such trades and diverging decisions by global policymakers are each playing a role. Some of these forces can be traced back years, while others emerged only recently.

Here are some of the key reasons for the swings.

A long stretch of low interest rates led investors to take more risks.

The buildup of risks in the financial system can partly be traced back to 2008, when the housing crisis prompted the Federal Reserve to cut interest rates aggressively and keep them low for years. That encouraged investors to seek returns from riskier bets, since borrowing was cheap and cash parked in safe assets like money market funds earned next to nothing.

Rates were also cut back to near zero in the early stages of the coronavirus pandemic, reviving these sorts of trades.

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IMAGES

Invasive Species Series 2020: Japanese Knotweed
Japanese Knotweed or Fallopia Japonica Uses, Benefits, Side Effects
Identifying Japanese knotweed characteristics
Japanese Knotweed
Japanese Knotweed
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COMMENTS

New Approaches on Japanese Knotweed (Fallopia japonica) Bioactive Compounds and Their Potential of Pharmacological and Beekeeping Activities: Challenges and Future Directions
New Approaches on Japanese Knotweed (Fallopia japonica) ... The continuous research on cancer prevention and treatment has led to some notable studies that have revealed the chemopreventive role of the Polygonum genus, notably P. cuspidatum. As cancer is the result of some biochemical processes that produce oxidative damage and possible death ...
New study counts the environmental cost of managing Japanese knotweed
New Swansea University research has looked at the long-term environmental impact of different methods to control Japanese knotweed. The invasive species has been calculated to cost more than £165 ...
We've found the best way to control Japanese knotweed
Our research has highlighted the most appropriate way to treat established Japanese knotweed stands and, surprisingly, a number of other methods which are poor or totally ineffective at field scale.
Assessing the relative impacts and economic costs of Japanese knotweed
Life cycle assessment scope. This study used a large-scale Japanese knotweed control field trial based in South Wales, UK, as a model system 23.While the aim of Jones et al. 23 was to assess ...
What's the most sustainable way of dealing with Japanese knotweed? Here
Back in 2018, our research group published the results of the world's largest Japanese knotweed trial, which is what informs how we currently tackle the plant. Sustainability
New Approaches on Japanese Knotweed (Fallopia japonica) Bioactive
Known especially for its negative ecological impact, Fallopia japonica (Japanese knotweed) is now considered one of the most invasive species. Nevertheless, its chemical composition has shown, beyond doubt, some high biological active compounds that can be a source of valuable pharmacological potential for the enhancement of human health.
Japanese knotweed is no more of a threat to buildings than other plants
Japanese knotweed remains a serious threat to Britain's biodiversity, ecosystems and the amenity value of land, but these very real threats should not be confused with what our research shows to ...
Optimising physiochemical control of invasive Japanese knotweed
Japanese knotweed, Fallopia japonica var. japonica, causes significant disruption to natural and managed habitats, and provides a model for the control of invasive rhizome-forming species. The socioeconomic impacts of the management of, or failure to manage, Japanese knotweed are enormous, annually costing hundreds of millions of pounds sterling (GBP£) in the UK alone. Our study describes the ...
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Infestations of Japanese knotweed can be problematic but new research may provide a solution. A new strategy for addressing a pesky plant has potentially been developed by researchers from NUI ...
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On 23 March, the new RICS Japanese knotweed and residential property professional standard comes into effect. By complete coincidence, that date is exactly ten years since its predecessor, the information paper Japanese knotweed and residential property, was launched. That paper introduced the first formal process for assessing Japanese ...
Japanese knotweed (Fallopia japonica): an analysis of capacity to cause
Fallopia japonica (Japanese knotweed) is a well-known invasive alien species in the UK and elsewhere in Europe and North America. The plant is known to have a negative impact on local biodiversity, flood risk and ecosystem services; but in the UK it is also considered to pose a significant risk to the structural integrity of buildings that are within seven m of the above ground portions of the ...
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Japanese knotweed was introduced to Europe by the German botanist and physician Philipp Franz von Siebold. Born in 1796, Siebold was commissioned in the Dutch army and travelled as a ship's ...
PDF Japanese Knotweed
in the winter (Beerling et al., 1994). New shoots will emerge from rhizomes in the spring. Monocultures of Japanese knotweed have been seen after stands are established. It has been observed that the presence of Japanese knotweed reduces local species diversity, providing evidence that it can suppress forest regeneration (Aguilera et al., 2010).
Japanese Knotweed
Japanese knotweed ( Fallopia japonica syn. Polygonum cuspidatum ), an herbaceous perennial member of the buckwheat family, was introduced from East Asia in the late 1800s as an ornamental and to stabilize streambanks. Knotweed is a highly successful invader of wetlands, stream corridors, forest edges, and drainage ditches across the country.
Japanese Knotweed
Distribution / Maps / Survey Status. Early Detection & Distribution Mapping System (EDDMapS) - Japanese Knotweed. (link is external) University of Georgia. Center for Invasive Species and Ecosystem Health. Provides state, county, point and GIS data. Maps can be downloaded and shared.
Japanese Knotweed research: New ways to treat invasive weed
New research into the long-term environmental impact of the methods used to control Japanese knotweed has been published. The invasive species can cause widespread damage to buildings and gardens. Weed removal specialists Complete Weed Control has part funded research at Swansea University. It comes as the calculated cost of damage caused by ...
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The one human study conducted using Japanese Knotweed found that, after 6 weeks supplementation of 200mg (40mg Resveratrol) daily, that extracted immune cells had 25% less translocation of NF-kB; NF-kB is a mediator of inflammation, and this was overall a reduction in inflammation. [34] The reduction in NF-kB activity resulted in less circulating TNF-a and IL-6 as well; two inflammatory ...
Cornell Cooperative Extension
Japanese knotweed stems are hollow and jointed. The leaves are alternate, broadly egg-shaped, and 3 to 6 inches in length. The plant is dioecious, so male and female plants both produce cream-colored flowers that vary slightly in appearance. Flowers appear in late summer and are found in erect clusters 4 to 5 inches long arising from the leaf ...
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Japanese knotweed can also be helpful in counteracting the inflammation and oxidative stress that can sometimes accompany physical exercise. In a 2013 double-blind, placebo-controlled human clinical trial, researchers gave 20 healthy male professional basketball players 200 mg of Japanese knotweed extract standardized to 20% trans-resveratrol ...
Japanese Knotweed
Japanese knotweed and the related giant, Bohemian, and Himalayan knotweeds are fast-growing and form dense stands, allowing little to no other vegetation to survive. It is semi-shade tolerant, but is most aggressive in full sun. ... There is one biocontrol insect for Japanese knotweed under study in New York; research release trials started in ...
Japanese knotweed
Japanese knotweed is a tall dense shrub that can rapidly grow to a height of 3-4.5 meters (10-15 feet). Arising in the spring from spreading underground rhizomes and a deep taproot, the hollow jointed stems are reminiscent of bamboo and assume an orange hue when mature. The simple ovate leaves are borne alternately along the stems and reach up to 15 cm (6 inches) in length.
This Invasive Weed Flowers In August. Kill It Before It Spreads!
Why Japanese Knotweed Is a Problem. Japanese Knotweed is native to East Asia, specifically Japan, China, and Korea. It was introduced to North America and Europe in the 19th century as an ...
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By Tripp Rogers and Travis Gannon Herbicide-resistant weeds are a leading problem in the turfgrass industry and may compromise the functionality and aesthetic quality of turfgrass systems. What is herbicide resistance? Herbicide-resistant weeds are not a new problem in turfgrass systems (or any agricultural system). Herbicide resistance is a selection process that develops through the repeated ...
Steadying the hands of time
The laser was the same variety used in CSACs, called a vertical cavity surface emitting laser, or VCSEL (rhymes with "pixel"). What's more, "Nichia had been looking for a new opportunity to showcase the value of its VCSEL with violet-blue wavelength," a Nichia spokesperson said. Dan lit up when he read a research paper about the laser.
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Development of a Novel Japanese Eel Myoblast Cell Line for ...
The present study investigates the isolation, analysis, and characterization of primary cultured cells derived from the muscle tissue of Japanese eel ( Anguilla japonica ), culminating in establishing a spontaneously immortalized myoblast cell line, JEM1129. We isolated satellite cells from eel muscle tissue to establish a foundation for cultured eel meat production. While initial cell ...
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Assessing the relative impacts and economic costs of Japanese knotweed management methods

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Scope for non-crop plants to promote conservation biological control of crop pests and serve as sources of botanical insecticides

Goal of the life cycle assessment

Life cycle assessment scope

Treatments selected for LCA

Description of treatment methods used in the LCA

Chemical knotweed treatment information

Integrated physical and chemical methods

Physical knotweed management

System boundaries and functional unit

Data inputs

LCA impact assessment (LCIA)

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Evaluating use of impact assessment method: results of sensitivity analysis

Evaluating endpoint impacts of knotweed management

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Post-application impacts of Japanese knotweed management methods

Costs versus benefits in IAP management

Conclusions

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New Approaches on Japanese Knotweed ( Fallopia japonica ) Bioactive Compounds and Their Potential of Pharmacological and Beekeeping Activities: Challenges and Future Directions

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Japanese knotweed is no more of a threat to buildings than other plants – new study

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Optimising physiochemical control of invasive Japanese knotweed

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Assessing the relative impacts and economic costs of Japanese knotweed management methods

Developing effective management solutions for controlling stinking passionflower (Passiflora foetida) and promoting the recovery of native biodiversity in Northern Australia

Introduction

Field trial site selection

Experimental design

Herbicide product selection and control treatment timing

Details of control treatments

Cut and fill application (TG b1, site 3)

Stem injection application (TG c1, site 3)

Integrated physiochemical control treatments

Excavation (TGs d2 and d3, site 1)

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Basal cover control response

Stem density control response

Light utilisation efficiency control response

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Conclusions: management of rhizome-forming IAPs

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