weed science research topics

REVIEW article

Emerging challenges and opportunities for education and research in weed science.

• 1 The Centre for Plant Science, Queensland Alliance for Agriculture and Food Innovation, The University of Queensland, Brisbane, QLD, Australia
• 2 Department of Agronomy, Muhammad Nawaz Shareef University of Agriculture, Multan, Pakistan
• 3 Department of Agronomy, Bahauddin Zakariya University, Multan, Pakistan
• 4 Centre for Environmental Management, Faculty of Science and Technology, Federation University Australia, Ballarat, VIC, Australia
• 5 Southern Agricultural Research Centre, Montana State University, Bozeman, MT, United States

In modern agriculture, with more emphasis on high input systems, weed problems are likely to increase and become more complex. With heightened awareness of adverse effects of herbicide residues on human health and environment and the evolution of herbicide-resistant weed biotypes, a significant focus within weed science has now shifted to the development of eco-friendly technologies with reduced reliance on herbicides. Further, with the large-scale adoption of herbicide-resistant crops, and uncertain climatic optima under climate change, the problems for weed science have become multi-faceted. To handle these complex weed problems, a holistic line of action with multi-disciplinary approaches is required, including adjustments to technology, management practices, and legislation. Improved knowledge of weed ecology, biology, genetics, and molecular biology is essential for developing sustainable weed control practices. Additionally, judicious use of advanced technologies, such as site-specific weed management systems and decision support modeling, will play a significant role in reducing costs associated with weed control. Further, effective linkages between farmers and weed researchers will be necessary to facilitate the adoption of technological developments. To meet these challenges, priorities in research need to be determined and the education system for weed science needs to be reoriented. In respect of the latter imperative, closer collaboration between weed scientists and other disciplines can help in defining and solving the complex weed management challenges of the 21st century. This consensus will provide more versatile and diverse approaches to innovative teaching and training practices, which will be needed to prepare future weed science graduates who are capable of handling the anticipated challenges of weed science facing in contemporary agriculture. To build this capacity, mobilizing additional funding for both weed research and weed management education is essential.

Introduction

Weeds, by virtue of their dynamic and resilient nature, represent a constant problem in agricultural production. The extent of weed infestation in the field depends on the agronomic practices used (for example, the type of crop and competitive ability of its cultivar, crop rotation, type of tillage, method and timing of fertilization, row spacing, seeding densities, and herbicides), soil type and fertility status, and prevailing environmental conditions ( Chauhan et al., 2012 ; Swanton et al., 2015 ). Being a botanical pest, weeds share the same trophic level as crop plants, and weed-crop competition for light, water, and nutrients results in substantial crop yield losses ( Swanton et al., 2015 ; Ramesh et al., 2017 ). A successful weed management program tends to integrate two objectives simultaneously: (i) prevent yield loss owing to weed competition in the short term, and (ii) avoid the addition of weed seed/vegetative propagules to the soil seed bank, to reduce weed densities in subsequent years ( Battle et al., 1996 ). The advent of diverse herbicide molecules for selective weed management has revolutionized contemporary agriculture, which has become more productivity-oriented than ever ( Shaw, 1964 ; Hamill et al., 2004 ).

Herbicide use for weed control in agricultural crops has made agricultural production simpler and economical ( Johnson et al., 2009 ), resulting in increased farm size. On the other hand, with the increased availability of selective herbicides for weed control, ecologically sustainable weed management as an integral component of cropping systems seems neglected. Although herbicide-based agricultural systems have benefited the farming community in many ways, continuous use and heavy reliance on herbicides has resulted in recurrent evolution of herbicide-resistant weeds, shifts in the spectrum of weed flora, and contamination of the surrounding environment, mainly through water movement ( Duary, 2008 ; Johnson et al., 2009 ). Consequently, there is an ever-growing consensus that the design of weed management systems with reduced reliance on herbicides seems essential to overcome the ill-effects associated with over-reliance on herbicide usage ( Bastiaans et al., 2000 ; Hatcher and Melander, 2003 ; O’Donovan et al., 2007 ). Therefore, the challenge faced by weed scientists is to develop innovative, ecologically sound, economical, and sustainable weed management systems, which can be integrated into existing and future cropping systems to bring a more diverse approach to weed management. Due to the genetic diversity and developmental plasticity of weed communities, weed management programs are now considered a continuous process within agricultural systems. New challenges, like herbicide-resistant biotypes, invasive plant species, and climate change have compelled weed researchers to develop cutting-edge technologies. The dynamic nature of weeds will continue to pose multi-dimensional problems for research scientists, and the quest to find innovative solutions to these challenges may once again revolutionize agriculture.

An additional confounding factor in this essential activity is that the goals and directions of weed science, which were clearly defined and universally recognized in the past, appear to have lost clarity in recent times ( Breen and Ogasawara, 2011 ). Several researchers have speculated whether weed science is moving in the right direction, and as a result questioned whether it has been able to make practical impacts on current emergent problems ( Wyse, 1992 ; Coble, 1994 ; Hall et al., 2000 ; Fernandez-Quintanilla et al., 2008 ; Moss, 2008 ; Breen and Ogasawara, 2011 ). Indeed many authors have specifically commented that the contribution of research into weed biology and ecology toward sustainable weed management programs is not up to the mark, and will require more systematic and focused work ( Mortensen et al., 2000 ; Chauhan and Johnson, 2010 ). Similarly, a later study suggested that, even in the herbicide era, knowledge of weed biology seems indispensable and could serve as the basis for practical weed management ( Van Acker, 2009 ). Diverse approaches that can relate weed biology studies to practical weed management are needed in this regard. Cousens (1999) argued that although weed threshold levels form an important area of research in weed science, these were seldom exploited practically. The author criticized the multitude of phenomenological experiments and over-dependence on simulating repetitive case studies, which have actually transformed weed science discipline into weed technology. Echoing the urging of Wyse (1992) , the study emphasized the need for a greater understanding of the basic principles underpinning weed science, besides a paradigm shift regarding critical research questions, changing from documenting “what occurs” to “why things happen.” Ward et al. (2014) in their critique of agricultural weed research, identified two major aspects for improvement of the weed science discipline: (i) scientific studies must be reoriented toward an understanding of weed biology, and (ii) management efforts to minimize the negative impact of herbicides. These authors criticized weed research conducted in recent years as being characterized by a high degree of repetitiveness, with an excess of purely descriptive studies that fail to relate novel hypothesis with established ecological and evolutionary facts. The authors urged the need to revisit agricultural weed research in a more holistic manner, comprising of a broader vision, a deeper theoretical justification, and an inter-disciplinary approach.

It has been suggested that the domain of crop protection, which intimately includes studies in weed science, needs to switch from technology-oriented to system-oriented tactics, which acknowledge innovation as a perfect blend of technological and non-technological (institutional and social) advancements across various levels, stretching from the field to the farm and the region ( Schut et al., 2012 ). In this respect, a rigorous introspective analysis of deliberated goals, resources in hand, directions, progress evaluation, and dissemination of results to the intended audience are key considerations for weed science in the foreseeable future, so that the discipline emerges stronger and more focused. Here, in a positive and constructive manner, we intend to highlight and prioritize the current issues for weed science research and education, identify challenges and opportunities, and critically assess what can be done to push the frontiers of weed science research and embrace horizons of quality-oriented weed science education. We would like to emphasize that the information presented in this article is deliberately general and not specific tailored to a particular climate or country.

Emerging Issues in Weed Science

Herbicide resistance and weed plasticity.

Over-reliance on herbicides as the sole tool to control weeds, and continuous use of herbicides with similar modes of action (MOA), have led to the evolution of herbicide-resistant weeds. Multiple herbicide-resistant species like the Amaranthus complex in corn and soybean, and grass weeds ( Echinochloa spp., species of Aegilops , Alopecurus , and Lolium , Phalaris minor Retz., etc.) in cereals and cereal-based rotations ( Avena fatua , Chloris truncata ), have seriously limited available herbicide options ( Beckie and Tardif, 2012 ; Vencill et al., 2012 ; Heap, 2017 ). The evolution of resistance to glyphosate in Sorghum halepense , and the dispersal of resistant biotypes both by seeds and rhizomes, first in Argentina and then in the United States ( Heap, 2017 ), is another significant example. In fact, 270 herbicides covering the global market represent only 17 MOA, and almost half of them act as acetolactate synthase (ALS), photosystem (PS) II, and Protox inhibitors ( Macías et al., 2007 ). The paucity of new/novel herbicide MOA discovery in the last 20 years has deterred weed control and prompted herbicide resistance ( Macías et al., 2007 ; Beckie and Tardif, 2012 ; Duke, 2012 ).

The widespread adoption of glyphosate-resistant crops and the use of a single herbicide (glyphosate) for weed control since the mid-1990s has diminished the quest for a new herbicide MOA ( Green, 2011 ; Beckie and Hall, 2014 ; Heap, 2014 ; Duke, 2015 ; Owen et al., 2015 ). The number of active ingredients used in at least 10% of the soybean area in the United States has dramatically declined from 11 in 1995 to just 1 in 2002 ( Green, 2011 ). Regulatory authorities sometimes deregister old herbicides for unscientific reasons; thereby limiting the diversity of chemicals available for weed control and increasing reliance on fewer active ingredients, leading to increased selection pressure ( Gressel, 2011 ). Most of the time the de-registration is due to these two reasons: (i) lack of efficacy due to increased resistance by the target weed species; and (ii) negative effects on the environment, due to excessive persistence, leaching properties or endocrine disruption in animal species. General weed problems in speciality crops/vegetables are on the increase due to the disappearance of old herbicides and the lack of new herbicide molecules.

High plasticity in weeds facilitates season-long germination in many species ( Zhou et al., 2005 ). With extended exposure to a given situation, plasticity enables weeds to adapt to a wide range of environmental conditions, resource constraints and intervention practices. Genetic diversity is the reason underpinning plasticity in weeds. Norris (1992) conducted isozyme analysis of several weed species, and concluded that even the same weed species collected from different areas showed variability at enzymatic levels. Similarly, Renton (2013) suggested that the evolution of resistance to herbicides is often modeled at a population level, but population-based methods ignore important aspects of variability between individuals within populations that may be essential drivers of resistance. Therefore, the research areas of genetics and evolution of weeds need to be strengthened. More in-depth studies are needed to develop an understanding of the various mechanisms of weed adaptation in response to changes in resources. There is much to learn about morphological, physiological, and genetic plasticity in weeds in response to the maternal environment, and understanding the effect of such plasticity on inter- and intra-specific competition could be useful for designing effective integrated weed management (IWM) programs ( Bajwa et al., 2015 ; Mahajan et al., 2015 ). Weeds respond to a change in agricultural practices. For instance, an increase in surface-germinating weeds (small-seeded dicots and grasses) due to increased adoption of conservation tillage (e.g., no-till) has been observed ( Price et al., 2011 ; Chauhan et al., 2012 ). The evolution of herbicide resistance in weed biotypes is another classical example of weed plasticity, which again emphasizes the need to understand the evolutionary dynamics of resistance development in weed species in order to develop effective mitigation programs ( Neve et al., 2009 ).

Gene Flow from Herbicide-Resistant Crops

Crop-related weed species are already an issue in herbicide-resistant crops in countries such as United States which adopted these crops a long time ago ( Green, 2011 ; Duke, 2015 ). However, these species are an emerging issues in countries, which are now adopting herbicide-resistant crops, for example, Malaysia. Some examples of these species are Oryza sativa f. spontanea (weedy/red rice) in direct-seeded rice, Aegilops cylindrical and Elytrigia repens in wheat, cruciferous weeds in rapeseed, Helianthus annuus in sunflower crop, Sorghum halepense and Sorghum bicolor (shatter cane) in sorghum. Worldwide, weedy rice has now become a major issue in rice production systems. The introduction of imidazolinone-tolerant rice has caused a huge infestation of weedy rice because of evolution of imidazolinone-resistant weedy rice ( Kraehmer et al., 2016 ).

The potential for gene flow from herbicide-resistant crops to wild/weedy relatives via pollen is a major concern. For example, weedy rice in the United States has evolved resistance to herbicides used in herbicide-resistant rice. The probability of gene flow may increase further if herbicide-resistant volunteer crops are followed in rotation with cross-pollinated crops, for example, corn with soybeans and oilseed rape/canola with sugar beets ( Beckie and Owen, 2007 ). The number of scientific papers disapproving the risks of gene flow from transgenic crops to feral weedy relatives far exceeds than those explaining “how to deal with this issue.”

Misconceptions about Integrated Weed Management and Neglected Areas of Research in Weed Science

There are misconceptions about the concept of IWM and the approach has not been followed in its true essence ( Harker and O’Donovan, 2013 ). The execution of real IWM programs demands more efficient and diverse approaches, rather than just relying on herbicides (e.g., sequential application and tank mixtures). To date, weed research is more oriented toward herbicide research and more funding is released in this direction. Several critics have argued that weed science is a “science of herbicides” rather than the “science of weeds” ( Wyse, 1992 ; Harker and O’Donovan, 2013 ). The authors examined weed science publications from 1995 to 2012, and found that more publications had been produced about chemical control rather than an integrated approach ( Harker and O’Donovan, 2013 ). Country wise, the United States had the highest publications in weed science. When related to population size, Switzerland, the Netherlands, New Zealand, Australia, and Canada had produced a disproportionately high number of articles on IWM. In IWM, the emphasis is on diversity of weed control methods rather than relying on one single method of weed control. Therefore, in its true sense, IWM means reducing the selection pressure for development of resistance to any single method of weed control.

Cultural manipulations (tillage, sowing time, planting pattern, cover crops, row spacing, fertilizer, and water management) in IWM may complement and substitute for herbicides by contributing “many little hammers” on weeds ( Liebman and Gallandt, 1997 ). Successful IWM tactics require advanced knowledge of weed ecology and biology ( Liebman et al., 2001 ). Weed biology and ecology (understanding of weed species and the role they play in agro-ecosystems) remained an orphan until recently, especially in developing countries, as it was overshadowed by the success of chemical weed control ( Gressel, 2011 ). Weed seed dormancy is an important consideration for IWM programs, which has implications for seed bank dynamics and periodicity ( Chauhan and Johnson, 2010 ), yet its prediction remains a challenging task due to the complex nature of functional relationships between biological processes and environmental variables. This issue has affected the overall prediction of extent and timing of weed emergence in agricultural systems. Increased seed dormancy and delayed germination have often been related to herbicide resistance ( Owen et al., 2015 ; Kumar and Jha, 2017 ). In a recent study, the glyphosate resistance and temperature mediated seed dormancy in some glyphosate-resistant populations was reported to reflect co-selection of resistance and avoidance imposed by decades of intensive cropping practices ( Kumar and Jha, 2017 ). True IWM options in oilseeds and pulses are very limited ( Sardana et al., 2017 ). For these crops, IWM with hand weeding was suggested in most of the research articles.

It has also been observed that early career weed scientists focus much of their research on herbicide efficacy, considering it a relatively easy field to publish their research, while IWM research requires more time and innovative ideas for publication. So in this way, IWM research is neglected. Considering the importance of IWM research, if at least one special issue on IWM research after 2–3 years is published in reputed journals, this could be an important step in promoting IWM research. A voluminous body of knowledge is available on the interaction of herbicides with other cultural practices. Nevertheless, the paucity of papers that evaluate economics, off-target damage, public health, education and training, ethical issues, and policy perspectives suggests that these issues are not considered priorities ( Hall et al., 2000 ; Davis et al., 2009 ).

Most of the publications dealing with weed biology and population dynamics are descriptive rather than explanatory. In order to have a better understanding of the subject matter, studies must unravel why weeds respond the way they do.

Herbicide Related Contamination

There is growing concern about herbicide residues in crop produce, soil and contamination of ground water. Besides contaminating soil and water, herbicides are known to interfere with soil enzymatic and microbial functions, which are essential for many reactions and transformations regulating soil health ( Hussain et al., 2009 ). Recently, the impact of herbicide application on soil function was reviewed ( Rose et al., 2016 ). The authors suggested that herbicide application could significantly alter soil function, for example, disruptions to earthworm ecology in soils exposed to glyphosate and atrazine and site-specific increases in disease resulting from the application of a variety of herbicides. The authors also suggested that sulfonylurea herbicides could affect N-fixation, mineralization, and nitrification at recommended or slightly higher application rates.

Lack of Trained Weed Scientists in Developing Countries

Unlike entomology and plant pathology, there are no or very few departments devoted solely to weed science in agricultural universities. Moreover, few if any university faculties are assigned to weed control in fruit orchards, ornamentals, aquatic, forest, and pasture. The number of faculties devoted to non-cropland weed management, turf, vegetables, ecology, and statistical issues pertaining to weed science is also limited ( Derr and Rana, 2011 ). Moreover, different degree-awarding institutes from various locations within a country, especially in developing countries, have almost homogenous weed science curricula, that do not consider regional variations in weed species, management practices, crops and cropping sequences, input levels, socio-economic backgrounds, and weed management skills of farmers.

Climate Change

Lack of precise information on the effect of climate change on agricultural pests, particularly weeds, remains a major impediment to portraying a true picture of this issue ( Ramesh et al., 2017 ). Nevertheless, the substantial environmental, ecological impacts and economic costs warrant the need to unravel these interactions on a priority basis ( Ziska and McConnell, 2015 ). Studies dealing with the effect of CO 2 have considered weeds and crop species as separate entities; nevertheless, under natural settings, weeds grow simultaneously with crops. Growing species in isolation to predict competitive effects as a function of elevated CO 2 may lead to inadequate quantification of crop-weed competition, since it is very rare to see a field infested with a single weed species ( Ziska and Goins, 2006 ). A limited number of studies have quantified the response of crops and weeds to CO 2 in competitive environments ( Ziska, 2004 ; Ziska and Goins, 2006 ), and there is an urgent need to conduct further research with mixtures of weeds and crops. Further, the impact of elevated CO 2 on the geographical distribution of weeds in managed ecosystems also needs attention ( McDonald et al., 2009 ). Studies of changes in floristic composition of weed communities in response to crop establishment methods, alternate moisture and tillage regimes, and other cultural practices are copious in the literature. However, studies focusing exclusively on changes in weed communities against the backdrop of elevated CO 2 are scant ( Koizumi et al., 2004 ), despite the probability that this could affect the overall structure and function of crop field ecosystems. Weeds once considered minor pests could became problematic due to a shift in their range caused by climate change ( Peters et al., 2014 ).

There are strong indications that herbicide efficacy is decreased at higher CO 2 concentrations ( Ziska and Teasdale, 2000 ; Ziska et al., 2004 ), due to CO 2 -induced morpho-physiological and anatomical changes in plants that interfere with uptake and translocation of herbicides ( Ziska and Teasdale, 2000 ; Manea et al., 2011 ). This implies an overall decrease in herbicide efficacy due to the dilution effect, rendering available herbicide options less effective and requiring more herbicide input to achieve the same level of weed control. Ziska et al. (2004) suggested that a greater root to shoot ratio and subsequent below ground dilution of glyphosate increased glyphosate tolerance at elevated CO 2 . Under such a scenario, perennial weeds are expected to become more problematic and difficult to control with glyphosate ( Ziska and Goins, 2006 ). Ziska et al. (2011) postulated that a rise in atmospheric CO 2 concentrations can have a profound effect on the biological processes of weed species, adding to their invasion potential. For example, these authors reported a 70% increase in the growth of Cirsium arvense , an invasive perennial C 3 weed species. Lee (2011) showed that increased temperature had a more significant effect on plant phenological development than elevated CO 2 . Increased temperature is expected to offset the benefits of increased CO 2 by limiting the reproductive output. If so, weed community dynamics and crop-weed interactions will need to be reassessed. There is no consensus over future rainfall prediction, except that it will become erratic, and consequently floods and droughts would become recurrent phenomena. Prolonged drought spells will favor C 4 and parasitic weeds like Striga hermonthica . In contrast, under increased moisture availability, weeds like Rhamphicarpa fistulosa would thrive ( Matloob et al., 2015 ). In rice, switching to direct seeding from transplanting in the quest of water saving has already increased weed competition and altered weed dynamics ( Matloob et al., 2015 ). Frequent rain showers will limit the “rain safe periods” available for herbicide application, besides promoting leaching of soil-applied herbicides and triggering subsequent ground water contamination ( Ramesh et al., 2017 ). Much of the research on climate change has focused entirely on manipulating the plant response to CO 2 concentration, while neglecting the rise in temperature and drought ( Bunce and Ziska, 2000 ; Fuhrer, 2003 ).

Climate change has led to altered distribution of weeds, for example, the appearance of Marsilea spp. under wetter conditions in rice in India. Water scarcity is driving the switch to direct-seeded rice, promoting recalcitrant grass weeds like Dactyloctenium aegyptium , Eleusine indica , Leptochloa chinensis , and weedy rice ( O. sativa ) in aerobic rice ( Chauhan et al., 2014 ; Matloob et al., 2015 ). In the wake of climate change, variations in temperature have caused shifts in weed flora. For example, Ischaemum rugosum Salisb. was commonly seen in the tropical part of India, but has now become very common in the northern part of India ( Mahajan et al., 2012 ). Increasing problems of parasitic weeds (e.g., Striga spp. , Orobanche spp.) under continuous cultivation of host crops (e.g., corn, sorghum, rice, sunflower, legumes, and vegetables), combined with low soil fertility particularly in the tropical countries, are observed. These weeds are expected to extend their geographic range under predicted climate change, affecting productivity of rainfed corn, sorghum, and rice crops. Unluckily, very few selective herbicides or other control options are available for their control, which is very difficult and is one of the obvious reasons why research has not been prompted in this regard ( Zimdahl, 2007 ). For instance, at present the use of imidazolinone-resistant corn (mutants with herbicide seed coating) is the only known herbicide mechanism to control the parasitic Striga ( Kanampiu et al., 2009 ). Infestation of wheat fields by Phalaris minor is expected to worsen with an anticipated rise in CO 2 ( Mahajan et al., 2012 ). Similarly, weedy rice will be more problematic in cultivated rice fields ( Ziska et al., 2010 ). In crux, this reflects the potential of increased weed pressure and subsequent competition in the rice-wheat cropping system of the Indo-Gangetic Plains.

Except for several short-term bioassay studies, research efforts to envisage weed biology against the backdrop of climate change continue at a slow pace, especially with regards to long-term, system-level experiments. Such research is not only complex and long-term, but also requires an inter-disciplinary approach. Hence, it seems less attractive to funding agencies, and is likewise, unappealing to weed scientists. Invasive plant species continue to expand in number and geographic range, and are an escalating threat to managed and natural ecosystems. Against the backdrop of climate change, invasion by alien plant species has emerged as the greatest challenge to ecosystem function and stability ( Hellmann et al., 2008 ). Derr and Rana (2011) pointed out a shortage of weed science faculties and dedicated courses aiming to improve invasive plant management, even in a technologically advanced country like the United States.

Opportunities

New avenues of weed science research.

To understand the changes in geographic distribution of weed species, weed surveying and mapping techniques need to be updated. Weed prediction maps and decision-making tools should be developed for each particular region. Knowledge of drones [unmanned aerial vehicles (UAVs)] should be imparted to weed scientists and crop consultants so that they can use this technology in developing decision-making tools ( Lopez-Granados, 2011 ). Remote sensing technologies offer oppurtunities to develop timely and accurate scouting and prescription maps to improve weed management decisions and protect the environment by applying more site-specific control measures (hand-weeding, targeted tillage, or spot spray) ( Shaw, 2005 ). The use of advanced optical-sensor based sprayer technology for site-specific herbicide applications is still in its infancy stage. Similarly, hyperspectral imaging to differentiate between crop and weed biotypes is a relatively new concept ( Okamoto et al., 2007 ), and would be a step forward in achieving precision weed control goals to reduce reliance on herbicides by applying them only where they are needed, compared with the current practice of broadcast herbicide applications. More research is needed on other precision herbicide application technologies, such as the use of shielded sprayers or herbicide banding, to reduce herbicide load and minimize herbicide runoff in furrow-irrigated cropping systems ( Davis and Pradolin, 2016 ). The potential utility of nanoherbicides and field robots for precise weed control can also be explored. For example, an Australian university has developed a fully-autonomous weed-killing robot (AG-BOT) and claimed that it would help in cutting the cost of weed control by 90% and potentially save the farm sector $1.3 billion a year ( Anonymous, 2016 ). Its abilities range from scouting, to knocking out weeds, to spot spraying, to the precision application of chemicals and fertilizers ( Pinter et al., 2003 ).

Nanotechnology can play a pivotal role in achieving more efficient and targeted herbicide application ( Pérez-de-Luque and Rubiales, 2009 ). Nanoherbicides as a “smart delivery system” provides an eco-friendly approach through reducing herbicide inputs, as well as providing control over where and when an active ingredient is released ( Pérez-de-Luque and Rubiales, 2009 ). Herbicide formulations with particle size ranging between 100 and 250 nm manifest higher solubility in spray mixture and absorption by plants ( Parisi et al., 2015 ). Additionally, a liposome-based biosensor has been reported to facilitate pesticide detection, which has implications for monitoring plant health and environmental conditions ( Vamvakaki and Chaniotakis, 2007 ). However, the advantages, risks and economic viability related to robotics and nanotechnology need to be assessed. There may be some environmental health risks posed by air-borne nanoparticles. They may impair translocation of water, nutrients, and photosynthates in plants by entering through vascular tissues. The nanoparticles may enter into the lung and blood stream of humans and cause inflammation, protein fibrillation, and induce genotoxicity ( Hoet et al., 2004 ). These risks could be avoided if the nanoparticle herbicides are injected into the soil.

The extraordinary seed production potential of annual weeds, coupled with the establishment of persistent seed banks, warrants the need for strategies that can avert seed input rather than merely focusing on reducing weed density to minimize crop yield losses ( Norris, 1999 ). In this direction, harvest weed seed control (HWSC) methods aimed at targeting weed seed production and their return to the soil weed seed bank can have a long-term impact on weed population dynamics under field conditions ( Shaner and Beckie, 2013 ). The concept is gaining popularity, and a non-chemical weed management tool named the “Harrington Seed Destructor” has been successfully implemented in Australia ( Walsh et al., 2012 ). Besides this tool, chaff carts and narrow windrow burning treatments have been shown to reduce Lolium rigidum emergence by 55% relative to the untreated plots ( Aves and Walsh, 2013 ).

Advances in molecular biology and biotechnology has revolutionized agriculture by enabling the development and commercialization of herbicide-resistant crops, which have been developed using both transgenic (integration of transgene) and non-transgenic (traditional plant breeding or mutagenesis) approaches ( Green, 2012 ). Herbicide-resistant crops, particularly glyphosate-resistant (Roundup Ready) crops, have been widely adopted by growers as they offered simple, effective and economical solutions for managing a broad spectrum of weeds, with improved crop yields, less inputs, and higher net returns ( Powles, 2008 ; Green, 2012 ). Advanced knowledge of the mechanisms, spread, and stability of herbicide-resistant weeds has helped in opening a new door for managing herbicide-resistant weeds in future. For example, three lessons from glyphosate resistance mechanisms, viz. target-site mutation, gene amplification, and altered translocation due to rapid vacuole sequestration, were learnt from glyphosate-resistant weeds ( Sammons and Gaines, 2014 ). The diversity of these types of mechanisms advanced our knowledge of plant physiology and molecular biology in the past 30 years, and yet “the agricultural chemical industry has not brought any new herbicides with novel sites of action to market in over 30 years, making growers reliant on using existing herbicides in new ways” ( Heap, 2014 ). The rapid evolution of glyphosate-resistant biotypes indicates that no herbicide is invulnerable to resistance ( Powles, 2008 ). The rapid evolution of glyphosate-resistant weeds (37 weed species worldwide) ( Heap, 2017 ) prompted the development of new herbicide-resistant, stacked-trait crops, in combination with the glyphosate-resistant trait ( Reddy and Jha, 2016 ). These include glyphosate-glufosinate in soybean, corn and cotton; glyphosate-ALS inhibitors in soybean, corn and canola; glyphosate-glufosinate-2,4- D in soybean and cotton; glyphosate-glufosinate-dicamba in soybean, corn, and cotton; glyphosate-glufosinate-HPPD inhibitors in soybean and cotton; glyphosate-glufosinate-2,4- D -ACCase inhibitors in corn; and glufosinate-dicamba in wheat ( Green, 2014 ). However, these stacked-trait crops will not be an ultimate weed management solution because several weeds have already evolved resistance to these herbicides, and an effective stewardship program is a must ( Reddy and Jha, 2016 ; Heap, 2017 ). Beckie and Hall (2014) stated that stacked herbicide-resistant (HR) traits (e.g., glyphosate+glufosinate+dicamba) would provide a short-term respite from HR weeds, but will perpetuate the chemical treadmill and selection of multiple-HR weeds. The only sustainable solution is for government or end-users of commodities to set herbicide-use reduction targets in major field crops similar to European Union member states, and include financial incentives or penalties in agricultural programs to support this policy.

Molecular biology tools have been utilized to understand the genetics of herbicide resistance evolution in weeds, but their practical implications to develop long-term approaches for herbicide-resistance mitigation in diverse agroecosystems are still limited. Molecular-based approaches for diagnosis of herbicide resistance in weeds are more efficient and less labor intensive than the traditional methods of conducting whole-plant herbicide dose-response bioassays ( Corbett and Tardif, 2006 ). DNA-based molecular markers provide a tremendous opportunity to study weed genetic diversity and hybridization among related weed species. Simple sequence repeats (SSRs), microsatellites, amplified fragment length polymorphisms (ALFPs), and inter-simple sequence repeats (ISSRs) have more recently been used in weed genomic studies ( Horvath, 2010 ). For instance, molecular markers were used to study the hybridization and transfer of herbicide-resistance trait between Amaranthus palmeri and A. tuberculatus and between A. tuberculatus and A. hybridus ( Trucco et al., 2005a , b ). PCR-based markers can be used to study weedy characteristics such as dormancy, seed shattering, and biotic and abiotic stress tolerance ( Horvath, 2010 ).

The novel “Omics” technology can revolutionize weed science. Genomics, proteomics, transcriptomics, and metabolomics are perceived as the beginning of a potential new era for the management of resistant weeds ( Neve et al., 2014 ) The advent of biochemical and molecular techniques, in conjunction with computational tools, has made it possible to incorporate protein modeling and crystallography to unravel target site mutations ( Tranel and Horvath, 2009 ; Horvath, 2010 ; Shaner and Beckie, 2013 ). This is a potential tool to screen for possible resistance before a herbicide is marketed ( Hollomon, 2012 ). Global gene-expression profiling techniques, such as microarrays, have been suggested as an effective tool in studying non-target site mechanisms ( Yuan et al., 2007 ). De novo whole genome sequencing, specifically EST (expressed sequence tag), can be used to identify various ‘candidate genes’ involved in mediating specific physiological and biochemical processes in a weed. These tools will also provide valuable insights into the response of weeds to biotic and abiotic stresses and crop-weed competition ( Tranel and Horvath, 2009 ; Horvath, 2010 ); hence, improving our understanding of the invasiveness of weeds, which would ultimately allow development of long-term, IWM strategies. Recently, a small subgroup of weed scientists has entered into the genomic era ( Gressel, 2011 ). There is a need to train young weed scientists in developing as well as developed countries in the field of molecular biology for a better understanding of crop and weed resistant traits.

The RNAi technology branded as BioDirect TM by Monsanto, although at an infant stage ( Hollomon, 2012 ), has produced a mirror copy of weed DNA in which target genes can be turned on and off. The exploitation of precise RNA segments capable of inhibiting enolpyruvyl-shikimate-3-phosphate synthase (EPSP) proteins in plants is a major breakthrough in reversing resistance ( Shaner and Beckie, 2013 ); however, this mechanism only applied to glyphosate.

The quest to identify the compounds that can induce weed seed germination on demand has been fulfilled by the discovery of novel compounds like karrikinolide ( Long et al., 2011 ). Karrikinolide is a biologically active component of smoke and a strong stimulant of weed seed germination ( Daws et al., 2007 ; Stevens et al., 2007 ). The practical application of this compound is to synchronize weed seedling emergence by stimulating germination, hence, it is a potential tool to deplete weed seed banks.

Weed Science Education

At the start of this reflection on weed science education, we see that students enrolled in weed research should be encouraged to conduct their trials in farmers’ fields, and so develop their mindset toward practical research. There is a need to ascertain why the intake of students in the weed science discipline is declining day by day, while on the other hand, problems and issues related to weed science are increasing. Identifying the causes for this decline in student intake, and finding workable solutions, is important for weed science. There are therefore two imperatives here (i) the area of weed science and weed management needs to be presented to the community in a more positive light, in order that potential students will be attracted to the discipline, and (ii) there is a need to develop interdisciplinary programs in weed science, to allow students to learn more about the complexity of weeds in farming systems, and eventually discover and implement new solutions ( Davis et al., 2009 ; Mortensen et al., 2012 ). New curricula in weed science should be focused on the role of genetics, evolutionary biology, molecular biology, and biochemistry.

We agree that degree programs in weed science with more diverse curricula, that emphasize locally important weed issues, and provide practical training in laboratory and field-based skills, will foster critical thinking and an ability to tackle complex weed situations. Additionally, it would be a good step forward if graduates from weed science could have more hands-on experience, funded through industry scholarships ( Davis et al., 2009 ). Such changes to weed science education will ensure the availability of technically trained manpower personnel (weed science professionals) to cope with future challenges in weed management.

Implementation of Need-Based Weed Research

We assert here that there is a need to develop weed management programs based on knowledge of weed ecology in relation to maternal environment, genetic and biochemical aspects, and molecular biology. In designing an appropriate weed science curriculum, the economics related to both weed-induced yield loss and weed control methods need to be incorporated. If farmers are not convinced of the economic feasibility of new weed control methods, then even sound and scientifically strong innovations may not be adopted. There is a need to identify weed threshold levels in important crops as part of precision weed control, so that weed control practices can become sustainable even with a reduced load of herbicides ( Norris, 1999 ).

Precision weed control systems may optimize the use of herbicides by allowing site-specific weed management and weed seed prevention from survivors, achieving zero seed thresholds, and therefore, may aid in mitigating herbicide-resistant weeds ( Reddy et al., 2014 ). Modeling studies on crop-weed competition need to be explored for making long-term weed control strategies. It is inevitable that long-term studies are needed in weed science, especially in weed ecology, weed resistance evolution, and herbicide-resistant crops. Therefore, private companies should come forward with funding for students’ and young scientists’ projects. We have identified that diversified weed control tactics are needed for sustainable weed control. IWM, including cover crops, tillage, row spacing, and crop density, needs to be explored for long-term weed control in different crops to minimize use of herbicides. At the same time, research in weed science must be oriented toward farmers’ needs and reflect their feedback in order to provide economical solutions to weed infestation, while protecting future generations through an insistence on truly and sustainable weed mitigation strategies. At the pragmatic level, farmers’ participation research regarding weed science needs to be strengthened in order to ensure the development of practical and sound decision-making tools ( Hall et al., 2000 ).

Future Directions

As a contribution to this debate, we offer here a 14 point discussion list, which we think should form the basis of a serious re-examination of the current approaches to the direction of research into weed science and to the preparation of new students who will take us into the future. The points are not given in a particular order.

(1) There is an urgent need to effectively extend the life of current commercial herbicides by reducing selection pressures on weeds, therefore preserving the genes for susceptibility. This demands:

• Improved and innovative strategies for the use of herbicides (i.e., use of full rates, adjuvants, tank mixtures, and rotations, with a focus on early-season weed management). These strategies are already practiced in developed countries but need to include in developing countries also.

• More research devoted toward the manipulation of non-chemical means, and the optimization and integration of these methods with chemical weed control methods.

• Strategic and eco-efficient use of herbicides aimed at improving efficiency through the development and promotion of precision application techniques. The goal of such a strategy is to maximize delivery to the intended weed flora, avoiding non-target application and minimizing negative environmental impacts.

• A change in perspective and approach from short-term weed control to sustainable weed management.

• Studies devoted to assessing the impact of herbicide usage on species richness, diversity, and abundance of resistant/tolerant weed species. The response of weed populations to herbicide-exerted selection pressure, and remedial measures, should be ascertained.

(2) Strengthening research efforts to discover alternate approaches to manage weeds, for example:

• The discovery of novel active ingredients, and commercialization of new herbicide products capable of controlling both susceptible populations and resistant weed biotypes.

• Identifying new morpho-physiological or biochemical traits conferring multiple herbicide tolerance, and the incorporation of such stacked traits into various crop types, to continue to benefit from existing chemical products, keeping in mind the pragmatic and judicious use of these herbicide-resistant crop traits to reduce environmental impacts and prevent selection of rare herbicide-resistance alleles in natural weed populations.

• More focused research on weed ecology in terms of reducing weed seed banks in the soil and use of HWSC methods.

• The development of stimulants and desiccants to manipulate germination and dormancy mechanisms of weed seeds, with the aim of reducing soil seed banks. The inherent and inducible karrikinolide response of weeds belonging to different families with contrasting dormancy status, in conjunction with variable regimes of light and temperature, should be investigated.

• The development and commercialization of state-of-the-art technologies [e.g., bio-control methods, RNAi (RNA interference), etc.].

(3) Research efforts are needed to refine IWM principles for various cropping systems and agro-ecological regions. More holistic research and development programs are needed to manage weeds over multiple seasons. The impact of long-term fertilization practices on weed species composition, abundance, diversity, and functional traits should be worked out across conventional and conservation tillage systems, while considering spatial heterogeneity of the landscape. This approach will help predict future weed problems, so that weed management approaches can be modeled in anticipation.

(4) Weeds can be exploited as a source of valuable genetic materials for crop breeding programs – breeding for abiotic stresses (salinity, drought, submergence, and temperature stress). Genes encoding functional substances should be cloned and introduced into crops to develop stress-tolerant ideotypes.

(5) Studies on the mechanisms of herbicide resistance have revealed that plants can evolve a fascinating biological arsenal as a defense. Unraveling the complexities in metabolic-based resistance is a challenge that has the potential to cause a paradigm shift in our understanding and management of resistant weeds. Basic and fundamental research on the mechanistic and genetic basis of resistance must contribute to discovering the missing links in the evolutionary path to herbicide-resistance at genotypic, population, and ecosystem levels. Future research must focus on questions about genetic variations versus novel resistance mutations, fitness benefits, and costs under herbicide selection, as well as the links between metabolic resistance and general detoxification pathways involved in stress-response dynamics.

(6) It has been suggested that the genotypic variation among crop cultivars responsible for weed tolerance can be exploited as an integral component of IWM programs ( Mahajan and Chauhan, 2013 ). Breeding weed-competitive (high early vigor) and allelopathic crops that suppress/kill weeds can help toward ecological weed management. Understanding the genetics of a crop’s allelopathic activity remains a germane issue to be researched ( Bunce and Ziska, 2000 ; Fuhrer, 2003 ). Coordinated breeding programs focusing on the location of genes involved in the production of allelochemicals, control of the allelopathic activity, and mapping the populations between allelopathic and non-allelopathic accessions can be crucial in this regard ( Fragasso et al., 2013 ). Identification of crop cultivars with strong allelopathic potential can contribute directly to weed suppression by their inclusion in crop rotation, or their use in breeding programs to incorporate allelopathic traits into future genotypes, making them more able to compete with and suppress weeds ( Aslam et al., 2017 ).

(7) Real-time integration of knowledge on agronomic weeds (history, biology, ecology, and control methods) with advancements in computer science and engineering could help secure environmental protection, agro-ecosystem sustainability, growers’ profit, and public health ( Singh et al., 2011 ). Development of efficient remote sensing and guidance systems capable of combining recognition (detection through field scouting) and application (spraying, cultivation, and mowing) modules into a single real-time platform is a critical area of research for decision support systems and site-specific weed management ( Young, 2012 ).

(8) More sophisticated computer-based simulation models capable of integrating available information and predicting competition and population dynamics are needed for a better understanding of weed-crop relationships across a range of weed management spectrums ( Renton and Chauhan, 2017 ). Against the backdrop of climate change, predictive modeling of weed distribution, range expansion, and invasion potential has become more critical than ever and needs to be finely-tuned and concomitantly updated to predict weed responses ( Clements et al., 2014 ). Besides prediction modeling, models for decision support are also needed to explain the likely outcome of different management interventions, associated costs, risks involved, and potential benefits.

(9) Assessing the fate and behavior of applied herbicides in various cropping systems remains a neglected area of research in developing countries. We understand that information on the fate and transport of herbicides in the environment is over-whelmed in the literature; however, most of this information is from the studies conducted in advanced countries. Far-reaching research is needed to quantify persistence and mobility of commonly used herbicides in the rice-wheat cropping system, and to explore their environmental fate. Residual herbicide analysis can be helpful in predicting the nature and level of contamination in the litho and hydrosphere, and the implications for the biosphere as a whole. Understanding these processes can yield information about introduction and degradation pathways into the environment, facilitating risk assessment ( Francaviglia and Capri, 2000 ) that can serve as a basis for modeling ( Nhung et al., 2009 ). Moreover, the impact of these persisted chemicals on succeeding crops also needs to be investigated.

(10) Focused research is needed to unravel mechanisms conducive to the success of alien invasive weeds and identify vulnerabilities, to inform monitoring, early detection and warning systems, assist development of regional and global databases, strengthen quarantine and management systems, assess ecological and economic impacts, and improve public awareness.

(11) The impact of climate change on crop-weed competitive outcomes needs to be studied, considering all possible combinations of plant-weed carbon fixation pathways, C 3 crops and C 3 weeds, C 4 crops and C 4 weeds, C 3 crops and C 4 weeds, and C 4 crops and C 3 weeds. To what extent, the so called “CO 2 fertilization” could compensate for other negative effects of climate change on crop-weed competition remains elusive. Competitive outcomes in managed and natural ecosystems pertaining to agricultural and invasive weeds need to be carefully studied considering the projected increase in CO 2 concentration, in conjunction with associated variations in other climatic variables such as temperature, rainfall, and drought. Against the backdrop of climate change, the production and concentration of secondary metabolites associated with allelopathic activity, geographic distribution of invasive weeds, and toxicity of poisonous weeds need to be explicitly assessed. Development and promotion of adaptive mechanisms and innovative practices to cope with weed problems under climate change is needed for sustainable crop production. A judicious analysis of their effectiveness, economic and ecological costs, and time span required is also essential in this regard.

(12) Apprehension about herbicide-resistant crops, such as negative impacts on biodiversity, gene transfer between wild relatives (particularly in the centers of crop origin), development of super weeds, and health issues, warrant the need for educational and awareness activities in collaboration with public groups, stakeholders, and policy makers, to foster the adoption process (particularly in Asia). The seed biotech industry should devise safe mechanisms of transgenic development to avoid introgression of resistant genes to related weeds.

(13) In order to harness the benefits of weed science for sustainable crop production, capacity building of scientists, teaching and training staff, extension personnel, and agri-graduates needs to be alleviated. Networking and collaboration of experts, knowledge sharing, and technology transfer from developed countries could benefit the overall weed science discipline in the developing world. Increased cooperation between complementary research groups of weed scientists (working in areas of IWM, herbicide efficacy, herbicide resistance, invasive plant management, ecological weed management, genetics, molecular biology, morphology and physiology of weedy traits, and ecosystem restoration) will be a step toward rediscovering and answering critical research questions, thereby enabling the weed science discipline to better respond to modern day vegetation management challenges and issues.

(14) Weed science educators/instructors should devise more experiential learning activities (fact-based learning processes that integrate tangible experiences, insightful observations, abstract conceptualization, and vigorous experimentation; reviewed by Atherton, 2002 ), and incorporate the same into their courses in order to promote understanding of the subject matter and concept retention ( Gallagher et al., 2007 ).

Weed science as an applied and integrative scientific discipline combines basic and applied sciences to better understand and manage weeds. Proper weed management promises food security via enhanced productivity and profitability, while safeguarding the natural resource base. Successful identification and alleviation of weed threat is one approach to enhance yield and abridge yield gaps. Weed scientists have a daunting job to deal with a plethora of problems that, although relevant, remain unexamined. Modern day weed management issues and challenges urgently demand weed scientists look beyond the herbicide efficacy/fate box and probe into basic and applied research pertaining to complex vegetation management in both natural and managed ecosystems that are currently tackled by plant physiologists, molecular biologists, and invasion ecologists.

To overcome various technical challenges, recent decades have witnessed significant progress in the form of site-specific weed management systems, herbicide-resistant transgenic crops, drones to monitor weed population dynamics, omics, novel herbicides, molecular biology tools, nanoherbicides, and simulation and decision support modeling. The human dimension is somewhat more difficult, and weed science has to grapple with issues such as farmers’ failure to appreciate the extent of weed menace, especially where the damage and losses are not apparent. Assessment of the environmental impact of weed management practices has formed a new and a relevant area of research in weed science. Against the backdrop of precision agriculture, advancements in the field of engineering and computer sciences can help quickly identify and control weeds with precise recognition and application modules. For weed science to thrive and respond to future weed problems, greater global collaboration will be required between this discipline and biological science, computer science, engineering, economics, and sociology. Channelizing and harnessing interdisciplinary collaboration and training of weed scientists, coupled with information exchange, could help solve complex challenges with more diverse and versatile approaches, and achieve greater consensus – so avoiding uncertainties and critiques.

Weed scientists should respond to their critics by taking part in reflection, introspection, and debate. In particular, steps should be taken to avoid a preponderance of repetitive and descriptive studies on herbicides. We believe that a paradigm shift in weed science will begin with a paradigm shift in the “way weed scientists think and pose critical research questions and hypotheses.” As weed scientists, we should acknowledge a general lack of diversity that currently exists in weed management programs. We can then enrich our tool kit by using exciting novel tools from other disciplines, and should seek the opinion of intellectuals from diverse scientific backgrounds. Future weed science is expected to be a perfect blend of different disciplines-all contributing to a unifying goal of sustainable weed management.

It is now well-known that increased global trade is also resulting in exotic weed spread, potentially creating alarming new situations in the wake of climate change. Therefore, advanced knowledge in weed science will be required to provide new tools for handling such complex emerging problems for weed management in the 21st century. As a direct consequence of this scenario, weed scientists will need to revisit the concept and tactics of IWM, since its non-chemical components are currently being given less priority by both public research institutes and the farming community, with continued reliance on synthetic chemicals. We urge that innovative and diverse teaching practices should be developed to prepare weed science graduates for the anticipated challenges of future agriculture. Currently, weed science research, education, and extension is lagging behind the priority needs of weed management in natural, agricultural and urban landscapes, and the situation is expected to worsen with climate change. Increased resource mobilization and funding could prove beneficial in this regard. The number of positions devoted to weed science research, teaching, and extension needs to be increased, especially in areas where acute shortages are evident (such as natural ecosystems and non-cropland weeds, and invasive plant management). In a similar way to other plant protection disciplines (plant pathology and agricultural entomology), weed science should also be promoted to be a major department of all agricultural universities, offering innovative graduate- and post-graduate degree programs.

Author Contributions

BC, AM, and GM developed the initial concept and outline and they took lead in expanding the content. FA, PJ, and SF contributed and edited the manuscript.

Conflict of Interest Statement

The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.

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Keywords : advanced technologies, climate change, herbicide resistance, integrated weed management, research scientist, weed ecology, weed research and education

Citation: Chauhan BS, Matloob A, Mahajan G, Aslam F, Florentine SK and Jha P (2017) Emerging Challenges and Opportunities for Education and Research in Weed Science. Front. Plant Sci. 8:1537. doi: 10.3389/fpls.2017.01537

Received: 11 July 2017; Accepted: 22 August 2017; Published: 05 September 2017.

Reviewed by:

Copyright © 2017 Chauhan, Matloob, Mahajan, Aslam, Florentine and Jha. This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY) . The use, distribution or reproduction in other forums is permitted, provided the original author(s) or licensor are credited and that the original publication in this journal is cited, in accordance with accepted academic practice. No use, distribution or reproduction is permitted which does not comply with these terms.

*Correspondence: Bhagirath S. Chauhan, [email protected]

Disclaimer: All claims expressed in this article are solely those of the authors and do not necessarily represent those of their affiliated organizations, or those of the publisher, the editors and the reviewers. Any product that may be evaluated in this article or claim that may be made by its manufacturer is not guaranteed or endorsed by the publisher.

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Article contents

Introduction, materials and methods, results and discussion, a survey of weed research priorities: key findings and future directions.

Published online by Cambridge University Press:  13 June 2023

We conducted an online survey of weed scientists in the United States and Canada to (1) identify research topics perceived to be important for advancing weed science in the next 5 to 10 years and (2) gain insight into potential gaps in current expertise and funding sources needed to address those priorities. Respondents were asked to prioritize nine broad research areas, as well as 5 to 10 subcategories within each of the broad areas. We received 475 responses, with the majority affiliated with academic institutions (55%) and working in cash crop (agronomic or horticultural) study systems (69%). Results from this survey provide valuable discussion points for policy makers, funding agencies, and academic institutions when allocating resources for weed science research. Notably, our survey reveals a strong prioritization of Cultural and Preventative Weed Management (CPWM) as well as the emerging area of Precision Weed Management and Robotics (PWMR). Although Herbicides remain a high-priority research area, continuing challenges necessitating integrated, nonchemical tactics (e.g., herbicide resistance) and emerging opportunities (e.g., robotics) are reflected in our survey results. Despite previous calls for greater understanding and application of weed biology and ecology in weed research, as well as recent calls for greater integration of social science perspectives to address weed management challenges, these areas were ranked considerably lower than those focused more directly on weed management. Our survey also identified a potential mismatch between research priorities and expertise in several areas, including CPWM, PWMR, and Weed Genomics, suggesting that these topics should be prime targets for expanded training and collaboration. Finally, our survey suggests an increasing reliance on private sector funding for research, raising concerns about our discipline’s capacity to address important research priority areas that lack clear private sector incentives for investment.

Weeds and weed management impose enormous economic, environmental, and social costs in both managed and natural ecosystems. Although progress has been made in identifying weed management practices that limit these costs, ongoing challenges such as climate change and evolution of herbicide resistance require continued innovation to reduce the negative impacts of weeds and weed management on natural ecosystems and to support sustainable development of managed ecosystems. Identifying research priorities to address such challenges is essential for guiding the rational allocation of resources at multiple levels. Prioritizing research areas that address emerging challenges and leverage emerging opportunities in weed science should be helpful for government agencies in allocating grant funding to various programs and determining funding levels and research foci within those programs. Similarly, academic institutions or individuals developing weed science curricula benefit from prioritizing emerging research needs relative to current capacity and areas of expertise.

Within the weed science discipline, past efforts to identify and reflect on research priorities have differed greatly in their scope, time horizon, and the practitioners or institutions they aim to represent. In terms of scope, research prioritization efforts have varied from those aimed at capturing a wide range of topics in weed science (e.g., Davis et al. Reference Davis, Hall, Jasieniuk, Locke, Luschei, Mortensen, Riechers, Smith, Sterling and Westwood 2009 ; Hall et al. Reference Hall, Van Eerd, Miller, Owen, Prather, Shaner, Singh, Vaughn and Weller 2000 ; Jordan et al. Reference Jordan, Schut, Graham, Barney, Childs, Christensen, Cousens, Davis, Eizenberg, Ervin and Fernandez-Quintanilla 2016 ; McWhorter and Barrentine Reference McWhorter and Barrentine 1988 ), to those focusing on specific subdisciplines such as herbicide resistance (e.g., Shaner and Beckie Reference Shaner and Beckie 2014 ), nonchemical weed management (e.g., Baker and Mohler Reference Baker and Mohler 2015 ), invasive species management (e.g., Bayliss et al. Reference Bayliss, Stewart, Wilcox and Randall 2013 ; Foxcroft et al. Reference Foxcroft, Pyšek, Richardson, Genovesi and MacFadyen 2017 ), and weed genomics (Ravet et al. Reference Ravet, Patterson, Krähmer, Hamouzová, Fan, Jasieniuk, Lawton-Rauh, Malone, McElroy, Merotto, Westra, Preston, Vila-Aiub, Busi and Tranel 2018 ). Others have focused on identifying weed research priorities to address not only economic outcomes, but also potential environmental and social impacts (Bagavathiannan et al. Reference Bagavathiannan, Graham, Ma, Barney, Coutts, Caicedo, Clerck-Floate, West, Blank, Metcalf and Lacoste 2019 ; Jordan et al. Reference Jordan, Schut, Graham, Barney, Childs, Christensen, Cousens, Davis, Eizenberg, Ervin and Fernandez-Quintanilla 2016 ; Neve et al. Reference Neve, Barney, Buckley, Cousens, Graham, Jordan, Lawton-Rauh, Liebman, Mesgaran, Schut and Shaw 2018 ). Time horizons have also varied from relatively short-term prioritizations to address well-documented threats such as herbicide resistance (Sarangi and Jhala Reference Sarangi and Jhala 2018 ) to long-term speculation about priorities for the more distant future (Westwood et al. Reference Westwood, Charudattan, Duke, Fennimore, Marrone, Slaughter, Swanton and Zollinger 2018 ). Past approaches to identify weed research priorities generally fall within three categories: (1) those reflecting the opinions of one or several individuals, based on their perceptions of the discipline (e.g., Chauhan et al. Reference Chauhan, Matloob, Mahajan, Aslam, Florentine and Jha 2017 ; Mortenson et al. Reference Mortensen, Egan, Maxwell, Ryan and Smith 2012 ; Wyse Reference Wyse 1992 ); (2) those based on intensive discussion with a broader but still limited range of invited scientists and/or stakeholders (e.g., Hall et al. Reference Hall, Van Eerd, Miller, Owen, Prather, Shaner, Singh, Vaughn and Weller 2000 ; Jordan et al. Reference Jordan, Schut, Graham, Barney, Childs, Christensen, Cousens, Davis, Eizenberg, Ervin and Fernandez-Quintanilla 2016 ; Neve et al. Reference Neve, Barney, Buckley, Cousens, Graham, Jordan, Lawton-Rauh, Liebman, Mesgaran, Schut and Shaw 2018 ; Ward et al. Reference Ward, Cousens, Bagavathiannan, Barney, Beckie, Busi, Davis, Dukes, Forcella, Freckleton and Gallandt 2014 ); and (3) those based on results and interpretation of survey instruments sent to members of professional societies or stakeholders involved in weed science at the national (e.g., Davis et al. Reference Davis, Hall, Jasieniuk, Locke, Luschei, Mortensen, Riechers, Smith, Sterling and Westwood 2009 ; McWhorter and Barrentine Reference McWhorter and Barrentine 1988 ) or regional level (e.g., Sarangi and Jhala Reference Sarangi and Jhala 2018 ; Stoller et al. Reference Stoller, Wax and Alm 1993 ).

Unsurprisingly, research priorities identified through these different approaches vary. Those working most directly with stakeholders in agricultural settings (e.g., farmers and consultants) generally place greatest emphasis on herbicide-related research targeting efficient control of weeds in specific crops (e.g., Sarangi and Jhala Reference Sarangi and Jhala 2018 ; Stoller et al. Reference Stoller, Wax and Alm 1993 ). Others place greater emphasis on understanding weed biology and ecology to support integrated or ecological weed management using a wider range of strategies (e.g., Chauhan et al. Reference Chauhan, Matloob, Mahajan, Aslam, Florentine and Jha 2017 ), especially in organic production systems or minor crops where chemical options are limited (e.g., Baker and Mohler Reference Baker and Mohler 2015 ). In addition, several groups have emphasized the need for transdisciplinary research to integrate agroecological and socioeconomic approaches in weed management (Neve et al. Reference Neve, Barney, Buckley, Cousens, Graham, Jordan, Lawton-Rauh, Liebman, Mesgaran, Schut and Shaw 2018 ) and to address challenging weed problems as part of broader efforts to advance ecosystem sustainability (Jordan et al. Reference Jordan, Schut, Graham, Barney, Childs, Christensen, Cousens, Davis, Eizenberg, Ervin and Fernandez-Quintanilla 2016 ). All of these perspectives and approaches are represented to different degrees within the Weed Science Society of America (WSSA) and reflected in the results and interpretation of previous surveys of WSSA membership (Davis et al. Reference Davis, Hall, Jasieniuk, Locke, Luschei, Mortensen, Riechers, Smith, Sterling and Westwood 2009 ; McWhorter and Barrentine Reference McWhorter and Barrentine 1988 ). While some observers have speculated that views regarding weed research priorities have become increasingly polarized (Ward et al. Reference Ward, Cousens, Bagavathiannan, Barney, Beckie, Busi, Davis, Dukes, Forcella, Freckleton and Gallandt 2014 ), little documented evidence is available to evaluate such claims.

The WSSA’s E6 Weed Research Priorities Committee has met annually for decades to discuss weed science priorities and to generate priority lists that are periodically communicated to members, funding agencies, and the general public. Historically, these priorities have relied heavily on the opinions of volunteer members of the E6 committee, with various levels of informal or formal input from the wider WSSA community. Formal surveys of membership occurred in 1987 (McWhorter and Barrentine Reference McWhorter and Barrentine 1988 ) and 2007 (Davis et al. Reference Davis, Hall, Jasieniuk, Locke, Luschei, Mortensen, Riechers, Smith, Sterling and Westwood 2009 ). In the 2007 survey, respondents were asked to rank 15 research areas that had been suggested as priorities by the E6 committee almost a decade earlier (Hall et al. Reference Hall, Van Eerd, Miller, Owen, Prather, Shaner, Singh, Vaughn and Weller 2000 ). Thus, the most recent formal prioritization of weed science research with broad input from weed scientists occurred 16 years ago and was based on research categories generated almost 25 years ago. Given the many challenges, opportunities, and advancements that have arisen within the weed science discipline since that time, the current WSSA Research Priorities Committee (E6) undertook a survey to gauge current opinions on a range of research areas in weed science.

The primary objectives of our survey were to (1) identify research topics perceived by weed scientists in the United States and Canada to be important for advancing weed science and management in the next 5 to 10 years and (2) gain insight into potential gaps in current expertise and funding sources needed to address those priorities. Secondary objectives included exploring associations between respondents’ professional characteristics (areas of expertise, years of experience, institution type, and study system) and their research priorities, as well as evaluating potential shifts in research emphasis and funding since the last survey in 2007.

The survey was developed by the WSSA Research Priorities Committee (E6) in spring of 2021 and implemented as an online survey using Qualtrics software in the fall and winter of 2021 and 2022 (see Supplementary Appendix for survey questions). In brief, respondents were asked to provide professional and demographic information; report their own broad areas of research expertise; rank and prioritize both broad and specific research categories; and identify important funding sources for their research.

To determine which research categories and topics to include in the survey, we reviewed those included in the 2007 survey (Davis et al. Reference Davis, Hall, Jasieniuk, Locke, Luschei, Mortensen, Riechers, Smith, Sterling and Westwood 2009 ) and made adjustments to reflect new research areas of perceived interest that have emerged since the last survey (e.g., precision weed management and robotics) and distinguish “broad” areas of research from more specific topics. The previous surveys asked respondents to rank 15 research topics ranging in scope from “Invasive Weeds” to “Nutraceuticals” (two of which were later combined into “Other” for analysis and publication). We chose nine broad research areas for prioritization and included 5 to 10 subcategories within each for subsequent prioritization. Our approach was similar to that used by McWhorter and Ballentine ( Reference McWhorter and Barrentine 1988 ), which included rankings of six broad “research needs,” each with a set of research subcategories.

The nine broad research areas selected for the survey (Figure  1 ) were intended to reflect typical groupings used by WSSA members to describe their areas of expertise and to encompass a wide range of topics of potential interest. However, it should be noted that comparisons of broad area rankings in this survey—as with previous surveys—should be interpreted with caution, as they represent non-independent, overlapping categories with inherent ambiguities and differences in scope. To partially address these issues, respondents were asked not only to rank broad categories from highest (“top”) to lowest, but also to categorize them as “high,” “medium,” or “low” research priority areas. For example, respondents struggling to decide whether research on Invasive and Aquatic Weeds (IAW) should be ranked higher than potentially overlapping areas (e.g., Weed Ecology) could place both in a single priority class (e.g., high). We thus had two sets of rankings for these broad areas—a sorted ranking from top priority to lowest priority and a qualitative ranking of high versus medium versus low priority.

Figure 1. Percentage of respondents indicating broad areas of weed science as (A) high-priority research areas, (B) their top research priority area, and (C) their own area(s) of research expertise. WM, Weed Management.

Within each of the nine broad research areas, research subcategories were selected by the E6 committee with input from two to five additional weed scientists with relevant expertise. Initial lists of potential subcategories were generated by the committee, circulated for comment to these selected experts, and revised based on their input. As with broad research areas, respondents were asked to both rank subcategories from top to lowest priority and indicate whether they were high, medium, or low priority. Respondents could rank subcategories within as many broad areas as they chose, regardless of their self-identified areas of expertise and where they ranked the broad research area.

In contrast to previous surveys conducted by WSSA (Davis et al. Reference Davis, Hall, Jasieniuk, Locke, Luschei, Mortensen, Riechers, Smith, Sterling and Westwood 2009 ; McWhorter and Ballentine Reference McWhorter and Barrentine 1988 ), the survey was not restricted to WSSA membership, but extended to a broader range of professional societies including affiliated societies and international weed science societies listed on the WSSA website. However, response rates were low for many other societies, so our survey primarily reflects views of scientists working within WSSA and its closest affiliates. In addition, due to low response rates from outside the United States and Canada ( n = 56), results presented here include only responses from those two countries. As with previous surveys, responses represent a convenience sample, not a random sample, and may not be representative of U.S. and Canadian weed scientists as a whole.

Following Davis et al. ( Reference Davis, Hall, Jasieniuk, Locke, Luschei, Mortensen, Riechers, Smith, Sterling and Westwood 2009 ), the results in this survey are presented primarily as binned response proportions to multiple-choice questions. The percentage of respondents selecting different choices (in multiple-choice questions) or classifying research areas or subcategories in different priority classes (in ranking questions) were calculated for all respondents and for different subcategories of respondents. For optional questions (e.g., subcategory rankings and funding questions), percentages were based only on the subset of respondents answering those questions, so the number of responses varied, as noted in the “Results and Discussion.” To determine associations between respondents’ professional characteristics (i.e., institution type, study system, areas of expertise) and their responses, we used two-way contingency tables (Davis et al. Reference Davis, Hall, Jasieniuk, Locke, Luschei, Mortensen, Riechers, Smith, Sterling and Westwood 2009 ; Gotelli and Ellison Reference Gotelli and Ellison 2004 ) implemented using PROC FREQ in SAS. In cases in which the number of respondents in specific professional categories were too small to conduct valid chi-square tests (i.e., expected counts in corresponding cells of contingency tables were <5), categories were aggregated to form larger subgroups before analysis. For example, respondents indicating that they conducted the majority of their research in “vegetables,” “fruits,” or “ornamental” crops were aggregated into a larger “horticultural” category. Similarly, for analyses of subcategory prioritization, respondent institution types for agronomic systems could be separated into “private sector” (industry) versus “public sector” (government and university) due to larger sample sizes.

Profile of Respondents

We received 475 responses from weed scientists in the United States (91% of respondents) and Canada (9% of respondents). Within the United States, respondents were fairly evenly distributed by region, with 30% from the Northeastern region, 28% from the Central region, 21% from the Western region, and 20% from the Southern region. The majority of respondents were members of WSSA (68%), representing approximately 23% (271 of approximately 1,200) of WSSA total membership. This response rate was almost identical to the 23% (304/1,330) rate obtained by Davis et al. ( Reference Davis, Hall, Jasieniuk, Locke, Luschei, Mortensen, Riechers, Smith, Sterling and Westwood 2009 ) in their survey of WSSA membership.

Respondents with <10 years of weed research experience represented 38% of the total, while those with 10 to 20 or more than 20 years of experience represented 22% and 40% of the total, respectively. The relatively low percentage of responses from midcareer (10 to 20 years) scientists could be due to fewer weed scientists in that category or to a lower response rate among them. The majority of respondents were from academia (55%), followed by industry (21%), government (15%), and other institutions (9%). This distribution of responses by institution was also almost identical to that of the 2007 survey (Davis et al. Reference Davis, Hall, Jasieniuk, Locke, Luschei, Mortensen, Riechers, Smith, Sterling and Westwood 2009 ). Respondents’ study system data were also similar to those reported for previous surveys, with the majority of respondents (53%) conducting research in agronomic crops, followed by horticultural crops (16%); natural terrestrial areas (9%); forage, pasture, or rangeland (5%); aquatic habitats (4%); turf (3%); and other (10%).

Prioritization of Broad Research Areas and Areas of Expertise

Among the nine broad research areas, Cultural and Preventative Weed Management (CPWM) received the highest rankings among all respondents, with 68% listing it as a high priority and 26% as their top priority (Figure  1 A and 1 B). Herbicides and PWMR were the next most highly ranked broad research areas, with approximately 50% of respondents ranking them as high priority and 16% to 19% as top priorities. These were followed by Physical and Biological Weed Management (PBWM) (42% high priority; 6% top priority), Weed Biology (32% high priority; 7% top priority), and Weed Genomics (31% high priority; 9% top priority). Those areas perceived as lower priorities included IAW, Weed Ecology, and Social and Economic Issues (SEI), with 22% to 26% of respondents ranking these categories as high priority and 5% to 6% as their top priority.

Ranking of broad research areas varied by the institution type of respondents and generally followed expected patterns (Table  1 ). Scientists working in the private sector gave highest rankings to priorities for addressing short-term challenges with potential to generate revenue (e.g., herbicides, robotics), while those in the public sector placed greater priority on research aimed at areas with relatively little incentive for private investment (e.g., CPWM, Weed Biology). Among industry respondents, 82% ranked Herbicides as a high priority compared with 46% from academia and 32% from government. In contrast, 73% of respondents from academia and government ranked CPWM as a high priority compared with 56% for those in industry.

Table 1. Percentage of respondents (n = 393) ranking categories as high priority a based on Institution type.

a Respondents were asked to indicate whether each area was “high,” “medium,” or “low"priority based on its “potential value for advancing weed science” in the next 5–10 years.

b Significance of chi-square test (df = 6); a value <0.05 suggests that respondents prioritized research areas differently based on their institution affiliations.

Rankings of broad categories also varied based on the primary cropping system or habitat of study of respondents (Table  2 ). For example, those working primarily in agronomic and horticultural cropping systems ranked Herbicides as a higher priority than those working in natural areas, while those working in natural areas gave higher priority to Weed Ecology. However, it should be noted that among respondents conducting the majority of their work in agronomic cropping systems, prioritization of several broad categories differed substantially based on their institutional affiliations (Table  2 ). In particular, agronomists working in the public sector were four times more likely to view Weed Ecology as a high priority compared with those from industry. Similarly, almost twice as many agronomists working in industry viewed herbicide research as a high priority compared with those working in the public sector.

Table 2. Percentage of respondents (n = 392) ranking categories as high priority based on primary study system. a

a Respondents were asked to indicate whether each area was “high,” “medium,” or “low” priority based on its “potential value for advancing weed science” in the next 5–10 years.

b Includes academic and government; an asterisk (*) indicates that responses of public sector agronomists differed from those from industry (chi-square test P-value <0.05).

c Includes vegetables, fruits or nuts, and ornamentals.

d Includes forage, pasture and rangeland.

e Significance of chi-square test (df = 18); a value <0.05 suggests that respondents prioritized research areas differently based on their study systems.

Respondents self-identified their areas of expertise, with Herbicides being the most commonly selected area (63% of respondents reporting expertise; Figure  1 C). CPWM was the second most commonly selected area of expertise, with 41% of respondents. In contrast, <20% of respondents reported expertise in the following broad research areas: IAW (18%), PWMR (8%), Weed Genomics (6%), and SEI (4%). Respondents’ reported area(s) of expertise varied by institution type and study system, but not by years of experience in weed research. Those with <10 years of experience had an almost identical distribution of reported broad areas of expertise compared with those with >20 years of experience. The lack of association between years of research experience and areas of expertise suggests that broad areas of expertise in weed science may not have changed much in the past 20 years. However, more detailed information would be needed to evaluate this assertion relative to alternative explanations. For example, it is possible that more experienced scientists have shifted their areas of expertise over time or that substantial differences in expertise are only apparent for research topics within broad categories. Because previous surveys did not document respondents’ areas of expertise, we cannot directly evaluate shifts in expertise over time. Our survey, however, provides a baseline against which future surveys can measure such changes.

Comparing respondents’ research priorities (Figure  1 A and 1 B) with their areas of expertise (Figure  1 C) reveals several discrepancies. Most notably, only 8% of respondents reported expertise in PWMR compared with >50% who rated it as a high priority. Similarly, five times as many respondents rated Weed Genomics and SEI as a high priority compared with the number reporting expertise in those areas. Low levels of expertise in these areas suggest a strong need to bolster collaboration and training in areas such as engineering, computer science, genomics, sociology, and economics to help address emerging research priorities. These needs are discussed in more detail for several of the broad research areas in the next section.

Subcategory Prioritization within the Nine Research Areas

CPWM was ranked as the top research priority among the nine broad research areas (Figure  1 A). CPWM was ranked highly by respondents regardless of institution type (Table  1 ) and years of experience. However, depending on their primary study systems, respondents prioritized CPWM differently (Table  2 ). For example, CPWM was a higher priority for respondents studying turf compared with those studying aquatic habitats. Among respondents studying agronomic cropping systems, those in the public sector ranked CPWM above those from industry.

Although CPWM was not an explicit category in the 2007 WSSA survey, several related areas of research including “Non-chemical Weed Management” and “Cropping System Ecology” were ranked far below the dominant categories of “Herbicide Efficacy” and “Herbicide Resistance” at that time (Davis et al. Reference Davis, Hall, Jasieniuk, Locke, Luschei, Mortensen, Riechers, Smith, Sterling and Westwood 2009 ). This result suggests that prioritization of research related to CPWM has increased relative to herbicide categories in the last 15 years, perhaps due to increasing frequency of herbicide resistance, limited development of herbicides with new mechanisms of action, and a growing emphasis on organic and nonchemical weed management (Birthisel et al. Reference Birthisel, Clements and Gallandt 2021 ; Mennan et al. Reference Mennan, Jabran, Zandstra and Pala 2020 ).

Among the 186 respondents choosing to rank subcategories within CPWM, 67% indicated expertise in this research area, with the vast majority (77%) working in cash crop systems (horticultural and agronomic crops) and the public sector (81%). Among this group of respondents, 86% ranked the subcategory Combining Multiple Weed Management Tactics as a high priority (Figure  2 A)—not surprising given its breadth. For example, combining herbicides with cover crop residue would count in this subcategory, as would preseason tillage combined with in-season cultural practices. Interestingly, older yet more complex tactics including Crop Rotation and Diversification and Cover Cropping ranked relatively high, with more than half of respondents considering these high priorities. Weed Seedbank Management and Harvest Weed Seed Control—the latter being a relatively new tactic in the United States—received intermediate rankings, while other cultural tactics including Weed-Suppressive Crop Cultivars, Targeted Resource Placement, and Preventing Dispersal were assigned relatively low priority, with <30% of respondents ranking these as high priority. In general, rankings of subcategories within CPWM were similar across respondent institutions and study systems, with the exception of Cover Cropping, which was viewed as a high priority by 54% of those from the public sector compared with only 34% of those from the private sector.

Figure 2. Prioritization of research subcategories within broad research areas focused on weed management: (A) Cultural and Preventative Weed Management, (B) Precision Weed Management and Robotics, (C) Herbicides, and (D) Physical and Biological Weed Management. Boxes are shaded based on the percentage of respondents rating the research subcategory as a high priority (black), medium priority (gray), or low priority (white).

Despite the high prioritization of CPWM, only about 40% of total survey respondents representing our broader sample (i.e., not just those further ranking subcategories) considered this one of their areas of expertise (Figure  1 C), suggesting a potential need for increased training and collaboration in CPWM practices. This result parallels that of the 2007 WSSA survey (Davis et al. Reference Davis, Hall, Jasieniuk, Locke, Luschei, Mortensen, Riechers, Smith, Sterling and Westwood 2009 ), in which respondents reported seeking collaborators with expertise in cropping-system ecology. On the other hand, interest in collaboration with experts in Non-chemical Weed Management was ranked very low at that time.

The high prioritization placed on CPWM practices is encouraging for those advocating the expansion of weed science beyond its traditional emphasis on chemical weed control. Given rapid increases in herbicide resistance, challenges with adoption of new herbicide-tolerant crop traits, and increasing herbicide costs, developing and utilizing various CPWM practices will be critical.

PWMR was highly ranked among the nine broad research categories, with 53% of respondents categorizing it as a high priority and 16% ranking it as their top priority (Figure  1 A and 1 B). This rapidly emerging area of weed management was not included as an option in previous surveys of weed research priorities (Davis et al. Reference Davis, Hall, Jasieniuk, Locke, Luschei, Mortensen, Riechers, Smith, Sterling and Westwood 2009 ) but is clearly viewed as a promising area for managing weeds in the near future.

The ranking of PWMR varied based on the respondent’s institution and cropping system or habitat of study (Tables  1 and 2 ). For example, respondents from industry ranked PWMR higher than those from academia or government (Table  1 ). Those weed scientists working in horticultural crops ranked PWMR higher than those working in other cropping systems or habitats (Table  2 ). Interest among respondents studying these specialty crop systems is likely driven by the high economic value, lack of effective herbicides, and high manual weeding costs of these crops (Fennimore and Cutulle Reference Fennimore and Cutulle 2019 ). Likewise, >50% of the respondents studying agronomic, forage, and turf systems ranked PWMR as a high priority compared with only 25% of respondents studying natural areas.

Among the 145 respondents choosing to rank subcategories within PWMR, only 18% indicated expertise in this research area, with the vast majority working in cash crop systems (81%). Among this group of respondents, Artificial Intelligence for Identification and Discrimination of Crops and Weeds and Vision Systems for Detection of Weed-Crop-Soil Characteristics were ranked as high priority by the highest percentage of respondents (Figure  2 B). Sub-priority ratings within PWMR did not vary substantially based on institution or study system, with the exception of Autonomous Robotic Weeder Testing and Development, which was ranked as high priority by 60% of those in the public sector, compared with only 35% of those from the private sector. In general, these priorities are consistent with those emphasized by Fennimore and Cutulle ( Reference Fennimore and Cutulle 2019 ); in their review of robotic weeders for specialty crops, they conclude that research to improve “Weed-Crop Differentiation” and “Improved Physical Weed Control Actuators” should be the top priorities.

Despite the perceived importance of PWMR for advances in weed science, only 8% of all respondents reported expertise in this area (Figure  1 C). This suggests a need for greater training of weed scientists in this priority area, coupled with greater collaboration across disciplines to address priority subcategories within it. Previous calls for greater interdisciplinary collaboration in weed science research (e.g., Davis et al. Reference Davis, Hall, Jasieniuk, Locke, Luschei, Mortensen, Riechers, Smith, Sterling and Westwood 2009 ; Ward et al. Reference Ward, Cousens, Bagavathiannan, Barney, Beckie, Busi, Davis, Dukes, Forcella, Freckleton and Gallandt 2014 ) have emphasized agroecology and other disciplines as diverse as economics, sociology, and psychology; our results suggest that engineering and computer science should be added to that list. Results from this survey also support the suggestion of Fennimore and Cutulle ( Reference Fennimore and Cutulle 2019 , p. 1773) that “weed science curricula for undergraduate and graduate students should be revised to include the basics of robotic engineering.”

Herbicides ranked among the top three broad priority areas, with 52% of respondents considering them a high priority and 19% as their top priority (Figure  1 ). The ranking of Herbicides varied based on the respondent’s institution type (Table  1 ) and cropping system or habitat of study (Table  2 ). For example, 82% of respondents from industry ranked Herbicides as their top priority, compared with only 46% for those from academia and 32% from government institutions (Table  1 ). The Herbicides category was ranked as a high priority by >60% weed scientists working with agronomic and turf systems compared with only 22% of respondents working in natural areas (Table  2 ). These results demonstrate that herbicides are still widely valued for weed control across various crop production systems. Chemical weed control is often preferred over other methods because of its ease of application, relatively low cost, and effectiveness (Shaner and Beckie Reference Shaner and Beckie 2014 ).

Among the 202 respondents choosing to rank subcategories within the broad area of Herbicides, 92% indicated expertise in this area, with 79% working in cash crop systems and 37% working in industry. Among these respondents, 82% ranked Herbicide Development and Discovery, and 58% ranked Evaluating Efficacy as high priorities (Figure  2 C). More than 40% of those respondents also ranked Sprayer Equipment and Application Technology, Crop Tolerance, and Off-Target Herbicide Movement as high priorities. In general, ratings within this area were similar regardless of institution type or study system, although a larger percentage of private sector respondents rated Herbicide Development and Discovery (83%) and Sprayer Equipment and Application Technology (55%) as high priority compared with respondents from the public sector (78% and 37%, respectively). The top prioritization of Herbicide Development and Discovery likely reflects the continued concern surrounding herbicide-resistant weeds undermining the efficacy of many commonly used herbicides and the perceived need for developing herbicides with new mechanisms of action (Ruegg et al. Reference Ruegg, Quadrantiand and Zoschke 2007 ).

Reported expertise in herbicide research among all respondents was high, with 63% indicating expertise in this area (Figure  1 C). This is not surprising, given that herbicides are the primary tool for weed control in many cropping systems and that herbicide research continues to be a high priority for the discipline.

More than 40% of respondents ranked PBWM as a high priority, but <10% ranked it as their top priority (Figure  1 A and 1 B); 26% of respondents identified as having expertise in this area (Figure  1 C). Prioritization of PBWM relative to other broad categories did not differ by institution type (Table  1 ) or by primary cropping system or study habitat (Table  2 ). The latter is surprising, given well-known differences in applications of these nonchemical approaches across study systems. For example, physical weed management has long been associated with horticultural cropping systems and biological weed management with management of invasive weeds in natural systems (Cuda et al. Reference Cuda, Charudattan, Grodowitz, Newman, Shearer, Tamayo and Villegas 2008 ; Fennimore et al. Reference Fennimore, Slaughter, Siemens, Leon and Saber 2016 ; Van Driesche et al. Reference Van Driesche, Hoddle and Center 2009 ). Why these historic differences were not reflected in our survey results is unclear.

Among the 109 respondents choosing to rank subcategories within PBWM, 52% indicated expertise in this area, with 68% working in cash crop systems. Overall, among these respondents, Biocontrol was ranked as high priority by >60%, followed by Mechanical Weed Management at 51%. Management using Other Physical Means (46%) or Heat Based Weed Management (38%) followed, with Mulching and Solarization and Livestock Grazing ranked as a high priority by 29% and 26%, respectively (Fig.  2 D). However, prioritization of several of these subcategories varied by the study system of respondents (data not shown). For example, Livestock Grazing and Biocontrol were ranked as high priority by 43% and 80% of respondents working in non-cash crops compared with 18% and 54% of those working in cash crop systems, respectively.

In the 2007 WSSA survey (Davis et al. Reference Davis, Hall, Jasieniuk, Locke, Luschei, Mortensen, Riechers, Smith, Sterling and Westwood 2009 ), only 10% of respondents sought collaborators with expertise in nonchemical weed management, which includes PBWM. This may help explain the relative paucity of current expertise in this area among survey respondents. Greater collaboration beyond WSSA membership and greater research and training emphasis in PBWM may be valuable for addressing important research priorities in this area.

Weed Biology

Weed Biology was ranked as a high research priority by a third of respondents and as a top priority by <10%, placing this category in the middle of broad category rankings (Figure  1 A and 1 B). The relatively low ranking of this broad area might be an indication that a considerable number of weed scientists believe that sustainable weed management can be achieved without an in-depth knowledge of the physiological and environmental factors that determine weed growth and development or that they consider that our current knowledge of those factors is sufficient to properly design and implement effective weed management strategies.

Prioritization of Weed Biology varied based on the respondent’s institution type (Table  1 ) but not on the study system (Table  2 ). Respondents from academic and government institutions were almost twice as likely as industry respondents to select Weed Biology as a high priority (Table  1 ).

It is interesting that although Herbicides were at least twice as likely to be considered a priority for those studying agronomic, horticultural, and turf systems compared with those studying natural areas, the perception of the importance of Weed Biology did not differ across management systems. Consistent ranking of Weed Biology might indicate that there is a common, basic recognition of the value of biological knowledge for weed management regardless of the system, despite relatively low ranking.

Among the relatively small number of respondents (53) choosing to rank subcategories within Weed Biology, 40% indicated expertise in this area, 81% were from the public sector, and 64% worked primarily in cash crop systems. Among these respondents, more than half ranked Reproductive Biology as high priority, followed by Seed and Propagule Physiology and Mechanisms of Herbicide Tolerance and Resistance (Figure  3 A). Forty percent of respondents rated weed Plant Interference, Emergence and Phenology Modeling, and Physiological Responses to Climate Change as high priorities. However, in several cases, subcategory ratings varied substantially based on the institution of respondents (data not shown). For example, 76% of private sector respondents rated Mechanisms of Herbicide Tolerance and Resistance as a high priority compared with 43% of those from the public sector. Likewise, only 12% of industry respondents considered Physiological Responses to Climate Change a high priority compared with 47% of those from the public sector.

Figure 3. Prioritization of subcategories within (A) Weed Biology, (B) Weed Ecology, and (C) Weed Genomics and Transcriptomics. Boxes are shaded based on the percentage of respondents indicating the research subcategory as high priority (black), medium priority (gray), and low priority (white).

Weed Genomics

Weed Genomics was considered a high priority by 31% of respondents, with 9% ranking it as their top priority (Figure  1 A and 1 B). This ranking was roughly on par with that of Weed Biology and well below rankings of the four broad areas more directly related to weed management. This relatively low ranking could be because research in weed genomics is still in its infancy and/or that many weed scientists responding to this survey may not see a clear connection between Weed Genomics and improved weed management.

Although the importance of genetic studies to provide insights into the discovery of new herbicide targets and an in-depth understanding of weed biology have long been recognized (Hess et al. Reference Hess, Anderson and Reagan 2001 ; Ravet et al. Reference Ravet, Patterson, Krähmer, Hamouzová, Fan, Jasieniuk, Lawton-Rauh, Malone, McElroy, Merotto, Westra, Preston, Vila-Aiub, Busi and Tranel 2018 ; Tranel and Horvath Reference Tranel and Horvath 2009 ), only recently has considerable effort been made in whole-genome sequencing of important weed species (Laforest et al. Reference Laforest, Martin, Bisaillon, Soufiane, Meloche and Page 2020 ; Patterson et al. Reference Patterson, Saski, Sloan, Tranel, Westra and Gaines 2019 ; Peng et al. Reference Peng, Abercrombie, Yuan, Riggins, Sammons, Tranel and Stewart 2010 ). For example, the recently established International Weed Genomics Consortium (IWGC) aims for a coordinated international effort to provide a platform for private and public collaboration to develop genomic tools and resources to stimulate global research in weed biology and management and to ensure there is no duplication of sequencing of weed species (Ravet et al. Reference Ravet, Patterson, Krähmer, Hamouzová, Fan, Jasieniuk, Lawton-Rauh, Malone, McElroy, Merotto, Westra, Preston, Vila-Aiub, Busi and Tranel 2018 ).

Among the 67 respondents choosing to rank subcategories within Weed Genomics, 27% indicated expertise in this area, with 79% working in cash crop systems and 30% working in industry. Among these respondents, Genome Sequencing of Top-ranked Problem Weeds and Development of User-Friendly Databases was the top rated subcategory, followed by use of Weed Genomics and Transcriptomics to Understand Genetic Diversity and the Evolution of Resistance (Figure  3 C). More than two-thirds of those prioritizing these subcategories identified these as high priority. The whole-genome sequencing of problem weeds is also a top priority of IWGC, with sequencing of several of the top-ranked weeds (Palmer amaranth [ Amaranthus palmeri S. Watson], waterhemp [ Amaranthus tuberculatus (Moq.) Sauer], barnyardgrass [ Echinochloa crus-galli (L.) P. Beauv.], horseweed [ Conyza canadensis (L.) Cronquist]) completed and available to the public. Whole-genome sequencing of several other weed species (e.g., perennial ryegrass [ Lolium perenne L.], giant ragweed [ Ambrosia trifida L.], common ragweed [ Ambrosia artemisiifolia L.], and wild radish [ Raphanus raphanistrum L.]) are in progress.

Only 6% of all survey respondents indicated expertise in Weed Genomics (Figure  1 C), suggesting a need for increased training of weed scientists in this area. Further, it is important that weed scientists establish collaborations with plant evolutionary biologists and experts in plant genomics to address key issues in this research area. Nonetheless, interest in weed genomics appears to have grown in the last 15 years, although direct comparisons with the 2007 survey are not possible, as only 2% of respondents considered weed genomics a top priority with respect to their primary stakeholders at that time (Davis et al. Reference Davis, Hall, Jasieniuk, Locke, Luschei, Mortensen, Riechers, Smith, Sterling and Westwood 2009 ).

Weed Ecology

The survey clearly indicated that Weed Ecology is not considered a high research priority among the majority of survey respondents (Figure  1 A and 1 B), although rankings varied greatly depending on their institutions (Table  1 ) and study system (Table  2 ). Overall, approximately 25% of respondents considered Weed Ecology a high priority, and only 6% ranked it as their top priority. Respondents from academic and government institutions were five and seven times more likely to consider Weed Ecology a high priority than industry respondents, respectively. Respondents working in agronomic, horticultural, and turf study systems generally rated weed ecology as lower priority than those working in natural areas, forage, rangeland, or pasture. However, priorities sometimes differed substantially among weed scientists within study systems. For example, among respondents working in agronomic cropping systems, a larger portion of those in academia (24%) viewed Weed Ecology as a high priority compared with those from industry (6%).

Among the 90 respondents choosing to rank subcategories within Weed Ecology, 62% indicated expertise in this area, with 61% working in cash crop systems and 92% working in academic or government institutions (with only 8% working in industry). Among these respondents, nearly two-thirds ranked Ecological Relationships between Crops and Weeds as a high priority, followed by Climate Change Adaptation, a category with some overlap in Weed Biology (Figure  3 B). However, for several subcategories, prioritization varied based on the study system of respondents. Most notably, >60% of respondents working in natural systems rated Biodiversity Conservation as a high priority compared with only 29% of those working primarily in cash crop systems. Despite the limited information on weed adaptations to climate change, the survey suggests that weed scientists are paying attention to climate change as a driver of future weed problems or challenges in management. The role of weeds as a source of ecosystem services was ranked as a high priority for half of respondents, which suggests that many weed scientists are open to exploring and even recognize the need of better understanding the role that weeds play in agricultural and nonagricultural ecosystems beyond interfering with production practices.

An interesting result of our survey is that relatively few respondents (33%) viewed the study of Population Dynamics and Demography as a high priority, despite the high prioritization of Ecological Relationships between Cropping Systems and Weeds. This suggests that respondents may not recognize the importance of plant density fluctuations over time as a key determinant of ecological relationship between crops and weeds.

In contrast with several other broad research areas, the percentage of respondents indicating that they had expertise in weed ecology was almost identical to the percentage that viewed it as a high priority. This result suggests that the level of training received by weed scientists responding to this survey roughly matches its perceived importance as an area of research.

The relatively broad and non-independent research area of IAW was categorized as high priority by 25% of respondents (Figure  1 A). These results must be viewed in light of the fact that only 15% of respondents reported having expertise in IAW (Figure  1 C) and that the majority of responses were drawn from members of WSSA, which has historically been a professional organization of researchers managing weeds primarily in agronomic cropping systems. In terms of rank, only 5% of respondents viewed IAW as their top research priority. However, this relatively low ranking in part reflects the breadth of this area, which would be on par with “agriculture weeds,” which was not a choice on the survey. Also, IAW includes elements of all of the other categories, so respondents were asked to choose to rank IAW broadly against other overlapping areas. Nevertheless, it seems clear that among survey respondents, IAW are of lower priority than other aspects of weed management.

The percentage of respondents ranking IAW as a high priority varied by institution type (Table  1 ) and study system (Table  2 ). It was ranked the highest among government employees (ranked high priority twice as often as it was by academics and four times as often as it was by scientists in industry), although intermediate among broad research areas within this institution type. The low ranking of IAW among respondents from industry likely reflects their primary emphasis on managing weeds in row crops. On the other hand, those working in natural areas ranked IAW the highest (Table  2 ), reflecting the ecosystems most impacted by these species.

Among the 100 respondents choosing to rank subcategories within IAW, 59% indicated expertise in this area, and 92% reported working in the public sector (only 8% from industry). Among these respondents, rankings of the subcategories (Figure  4 A) somewhat reflects the opportunities perceived to have the greatest impact on mitigating these damaging species. The top ranked subcategory was Early Detection and Rapid Response (EDRR), with about 80% of respondents ranking it as high priority, followed by Management, with 70% of respondents. Prevention has long been considered the stage at which the greatest return on investment can be achieved (Keller et al. Reference Keeler, Lodge and Finnoff 2007 ), with the subcategory Risk Assessment serving that role (ranked fifth in our survey), and EDRR being most effective post-introduction at limiting the negative impacts of invasive species. High prioritization of Management among survey respondents reflects an urgent need of land managers, who have many fewer tools and options for managing invasive and aquatic species relative to their counterparts in agronomic systems. The non–management related themes (e.g., traits, rapid evolution, distribution models) were ranked relatively lower, although they remain important areas of research in the invasive species community.

Figure 4. Prioritization of subcategories within (A) Invasives and Aquatics and (B) Social and Economic Issues. Boxes are shaded based on the percentage of respondents indicating the research subcategory as high priority (black), medium priority (gray), and low priority (white).

The number of respondents who identified as having expertise in IAW was low relative to the more agronomically related weed management disciplines (Figure  1 ). This reflects the impression of the distribution of “weed scientists” who work in this area, though there are perhaps orders of magnitude more researchers with expertise in IAW who do not consider themselves weed scientists and are not affiliated with WSSA, and thus did not respond to, or never saw, our survey. This highlights an opportunity to engage the broader IAW research community, as happened in 2003 with the joint WSSA/Ecological Society of America meeting.

SEI was the lowest-ranked broad research area among respondents, with <25% ranking it as a high priority and only 5% ranking it as their top priority (Figure  1 A and 1 B). This is not surprising, given that <5% of respondents reported expertise in this area (Figure  1 C) and that it encompasses a wide range of issues viewed perhaps as beyond the scope of the weed science discipline. Nonetheless, the relatively low ranking of SEI suggests that calls for more inter- or transdisciplinary research integrating social and economic perspectives (e.g., Jordan et al. Reference Jordan, Schut, Graham, Barney, Childs, Christensen, Cousens, Davis, Eizenberg, Ervin and Fernandez-Quintanilla 2016 ; Neve et al. Reference Neve, Barney, Buckley, Cousens, Graham, Jordan, Lawton-Rauh, Liebman, Mesgaran, Schut and Shaw 2018 ; Ward et al Reference Ward, Cousens, Bagavathiannan, Barney, Beckie, Busi, Davis, Dukes, Forcella, Freckleton and Gallandt 2014 ) to solve “wicked problems” such as herbicide resistance (Jussaume et al. Reference Jussaume, Dentzman and Owen 2019 ) have not gained widespread appreciation among weed scientists responding to this survey.

The prioritization of SEI did not vary by institution type (Table  1 ) but did differ according to the study system of respondents (Table  2 ). In particular, scientists working in natural systems and forage habitats were roughly twice as likely to rank SEI as high priority compared with those in agronomic or horticultural systems.

Among the 69 respondents choosing to rank subcategories within the SEI research area, 16% reported expertise in this area, with 68% working in cash crop systems and 78% in the public sector. Among these respondents, the highest-ranked subcategory was Behavioral Decision Research, followed by Economic Impacts of Weeds and Weed Management (Figure  4 B). The lowest-ranked subcategories included Costs, Benefits and Barriers to Transdisciplinary Research, Impacts of Weeds and Weed Management on Human Health, and Labor Policy. However, in some cases, prioritization varied considerably based on institution type or study system. Most notably, those from the private sector were more than twice as likely to rate Consumer Values Regarding Weed Management as a high priority (67%) compared with those working in the public sector (30%), perhaps a reflection of their desire to understand and overcome negative perceptions of herbicides or genetic modification among consumers. In addition, those working in natural systems were much more likely to rate Impacts of Weeds on Human Health and Safety as a high priority (50%) compared with those working in cash crop systems (19%).

These ratings suggest greater interest among respondents in narrow farm-level or weed-level economic issues, rather than research addressing broader social issues or policy. This result may be discouraging to those who advocate for integration of social and economic approaches to balance trade-offs between private and collective interests related to weed management challenges (e.g., Bagavathiannan et al. Reference Bagavathiannan, Graham, Ma, Barney, Coutts, Caicedo, Clerck-Floate, West, Blank, Metcalf and Lacoste 2019 ; Jordan et al. Reference Jordan, Schut, Graham, Barney, Childs, Christensen, Cousens, Davis, Eizenberg, Ervin and Fernandez-Quintanilla 2016 ; Ward et al. Reference Ward, Cousens, Bagavathiannan, Barney, Beckie, Busi, Davis, Dukes, Forcella, Freckleton and Gallandt 2014 ).

Funding for Research

The four sources of funding identified by the highest number of survey respondents as important for weed science research were (1) private industry, (2) commodity groups, (3) U.S. Department of Agriculture–National Institute of Food and Agriculture (USDA-NIFA), and (4) state funding (Figure  5 ). More than two-thirds of survey respondents indicated that private industry was an important source of their research funding, and 32% ranked it as their top funding source. Commodity groups ranked second, with 54% listing it as an important source, and 21% as their top source. Of federal agencies, USDA-NIFA was identified as an important source of funding by the highest number of respondents (43%) and the top source of funding by 23%. Other federal funding agencies, including USDA–Natural Resources Conservation Service (USDA-NRCS) and USDA–Animal and Plant Health Inspection Service (USDA-APHIS), were identified as important by 10% to 20% of the respondents. The Army Corps of Engineers, National Science Foundation (NSF), and U.S. Agency for International Development (USAID) were identified as important by <10% of the respondents. Other federal agencies not specifically included in the survey, such as USDA–Agriculture Research Service (USDA-ARS), U.S. Department of Transportation (DOT), and U.S. Department of Defense (DOD) were identified by 16% of the respondents as important. State funding was identified as an important source by 38% of the respondents, but as the top source by only 8%. Nongovernmental organizations (NGOs) or foundations were selected as important sources of funding by 10% of the respondents.

Figure 5. Importance of different funding sources for U.S. respondents. Percentage of respondents indicating that the source is important (gray bars) or their top (black bars) funding source. NGO, nongovernmental organization; NSF, National Science Foundation; USAID, U.S. Agency for International Development; USDA-APHIS, U.S. Department of Agriculture–Animal and Plant Health Inspection Service; USDA-NIFA, U.S. Department of Agriculture–National Institute of Food and Agriculture; USDA-NRCS, U.S. Department of Agriculture–Natural Resources Conservation Service.

While these composite data are informative, it is important to note that significant differences in responses were identified by institution type (Table  3 ). Private industry and commodity groups were an important source of funding not only for those in industry—as expected—but also for those in academia and, to a lesser extent, those in government (Table  3 ). Approximately two-thirds of academic respondents identified commodity group and private industry funding as important, compared with 25% to 33% of government respondents. A much higher percentage of academic respondents (59%) identified USDA-NIFA as an important source of funding, compared with those from industry and government, and a higher percentage of government respondents identified state funding and other federal sources as important, compared with industry and academic respondents.

Table 3. Percentage of U.S. respondents (n = 297) ranking funding sources as important, by institution type. a

a Abbreviations: NGO, nongovernmental organization; NSF, National Science Foundation; USDA-APHIS, U.S. Department of Agriculture–Animal and Plant Health Inspection Service; USDA-NIFA, U.S. Department of Agriculture–National Institute of Food and Agriculture; USDA-NRCS, U.S. Department of Agriculture–Natural Resources Conservation Service.

b Significance of chi-square test; a value <0.05 suggests that the percentage of respondents considering a source important varied by insitution type or study system.

Funding sources also varied by the study system of respondents (Table  4 ). Funding from private industry was identified as particularly important for those working in agronomic, turfgrass, and forage systems (>75% reporting as important), followed by horticultural crops (53%) and aquatic study systems (42%). In contrast, only 19% of those working in natural (terrestrial) study systems reported private industry as an important funding source. Similarly, commodity group funding was identified as important primarily for those working in agronomic, turfgrass, and horticultural study systems. Commodity funding was reported as particularly important for public sector respondents studying agronomic systems (81% reporting as important). Among public sector funding sources, USDA-NIFA was identified as important by 78% of respondents studying horticultural systems, compared with 47% of agronomy respondents working in the public sector and 23% of those studying natural areas. In contrast, those studying aquatic systems most often reported funding from state government sources (92%) and the Army Corps of Engineers (67%) as important. State funding was also considered an important funding source by >50% of those studying natural areas and forage crops and 37% of those studying horticultural crops, but only 22% of those studying agronomic cropping systems. USDA-NRCS and USDA-APHIS funding were important funding sources primarily to respondents studying natural areas and forage cropping systems.

Table 4. Percentage of U.S. respondents (n = 297) ranking funding sources as important, by study system. a

b Includes academic and government; an asterisk (*) indicates that important funding sources for public sector agronomists differed from agronomists from industry (chi-square test P-value <0.05).

d Includes forage, pasture, and rangeland.

e Signifcance of chi-square test (df = 6); a value <0.05 suggests that the percentage of respondents considering a source important varied by insitution type or study system.

Differences in the importance of funding sources based on study system and institution generally followed expected patterns. Commercial funding (private industry and commodity group) was important primarily for those working in agronomic and horticultural cropping systems, reflecting the important market these crops represent to private industry and greater availability of checkoff dollars for these commodity groups. As expected, public funding sources at the state and federal level were more important for those working in natural areas and aquatic systems, where private sector incentives for investment are lower.

Results from this survey suggest that commercial funding (private industry and commodity group funding) represents an important source of support for weed science research. Among survey respondents, 53% reported commercial funding as their top source (59% among WSSA members) compared with only 43% from the 2007 survey of WSSA members (Davis et al. Reference Davis, Hall, Jasieniuk, Locke, Luschei, Mortensen, Riechers, Smith, Sterling and Westwood 2009 ). This trend is consistent with reported shifts in funding sources for U.S. agricultural research in general over this time period. For example, Nelson and Fuglie ( Reference Nelson and Fuglie 2022 ) reported that public sector spending for agricultural research has declined by a third over the past two decades. During roughly the same time period, private sector funding for research and development from agricultural input industries increased sharply (Fuglie and Nelson Reference Fuglie and Nelson 2022 ), although the distribution of that funding to weed scientists is unclear. This shift in funding sources raises concerns regarding our capacity to address research questions in weed science with relatively little private sector incentives for investment.

The Way Forward

We received 475 responses to the survey, including approximately 25% of the membership of WSSA. Despite the inherent limitations and biases of surveys like this one, we believe the results reflect opinions of a broad range of weed scientists associated with WSSA and some of its affiliates. Furthermore, the information gathered here provides useful discussion points for policy makers, funding agencies, and academic institutions as they consider allocation of resources for research and training. Although it is challenging to interpret rankings of overlapping research categories that vary in scope, survey results support several broad conclusions worth emphasizing.

Perhaps most notably, our survey suggests a strong interest in broadening weed science research beyond the historic emphasis on herbicides toward several other areas of management. In the previous WSSA survey conducted in 2007 (Davis et al. Reference Davis, Hall, Jasieniuk, Locke, Luschei, Mortensen, Riechers, Smith, Sterling and Westwood 2009 ), herbicide-related topics, including “Herbicide Efficacy Enhancement” and “Herbicide Resistance” were the top two research priorities, far surpassing other topics included in that survey. Although herbicide-focused research clearly remains an important priority today (>50% of respondents indicated it was a high priority), CPWM led the current list of broad research areas (Figure  1 ), with subcategories such as Crop Rotation and Diversification Strategies and Cover Cropping ranked as high priority by >50% of respondents. Our survey also indicates a strong interest in research in the emerging area of PWMR, with >50% of respondents considering this an important research priority. Artificial Intelligence for Weed ID and Vision Systems for Detection of Weed-Crop-Soil Characteristics were ranked as particularly important research subcategories within PWMR deserving of public support.

Despite shifts in perceived research priorities since 2007, our survey suggests that broad areas of weed science expertise have not changed much in that time, and our discipline’s ability to address research areas that it considers important may be limited as a result. Comparing survey respondents’ broad areas of expertise with their research priorities (Figure  1 A vs. C), several potential gaps are evident. Most notably, respondents to this survey are underequipped to directly address priorities in the area of PWMR. Similarly, there appears to be a mismatch between expertise in Weed Genomics and SEI and their perceived importance to our discipline.

Given discrepancies between perceived research priorities and expertise in several research areas, our survey suggests that the weed science discipline would benefit from efforts to increase training and collaboration in areas such as engineering, computer science, genomics, and economics to help address our broad research priorities. While efforts are underway to broaden collaboration and training in some of these areas (e.g., the IWGC), more work is clearly needed.

Calls for greater collaboration and training across disciplines to address weed research priorities are not new (e.g., Davis et al. Reference Davis, Hall, Jasieniuk, Locke, Luschei, Mortensen, Riechers, Smith, Sterling and Westwood 2009 ; Neve et al. Reference Neve, Barney, Buckley, Cousens, Graham, Jordan, Lawton-Rauh, Liebman, Mesgaran, Schut and Shaw 2018 ; Ward et al. Reference Ward, Cousens, Bagavathiannan, Barney, Beckie, Busi, Davis, Dukes, Forcella, Freckleton and Gallandt 2014 ; Wyse Reference Wyse 1992 ). For example, Davis et al. ( Reference Davis, Hall, Jasieniuk, Locke, Luschei, Mortensen, Riechers, Smith, Sterling and Westwood 2009 ) concluded, based in part on their interpretation of 2007 survey results, that “if it is to remain relevant,” the weed science discipline must broaden its scope beyond herbicide efficacy and encourage greater integration of topics with a “complex systems” focus. Our survey suggests that, in terms of research priorities, some movement in this direction has occurred since 2007, as evidenced by the top ranking of CPWM and the subcategory Combining Multiple Tactics. However, the relatively low ratings of Weed Biology, Weed Ecology, and Weed Genomics suggest that many respondents do not believe that expanded research in these areas is critical for the development of successful integrated weed management programs. Additionally, self-identified expertise in these topics is similar between early-career and later-career weed scientists. The low rankings of SEI also suggest that the majority of weed scientists do not prioritize integration of social and economic approaches for solving weed management challenges such as those suggested by Bagavathiannan et al. ( Reference Bagavathiannan, Graham, Ma, Barney, Coutts, Caicedo, Clerck-Floate, West, Blank, Metcalf and Lacoste 2019 ) and increasingly emphasized by federal agencies (e.g., USDA-NIFA) supporting weed science research (Jordan et al. Reference Jordan, Schut, Graham, Barney, Childs, Christensen, Cousens, Davis, Eizenberg, Ervin and Fernandez-Quintanilla 2016 ).

Identification of research priorities is an important first step, but progress in addressing those priorities depends critically on availability of the funding and expertise to do so. Although a detailed characterization of respondent funding levels was beyond the scope of this survey, our results suggest a shift toward an increased reliance on private sources of funding since 2007. This apparent shift is consistent with reported decline in public sources of funding for agricultural research in general over this time period (Nelson and Fuglie Reference Nelson and Fuglie 2022 ) and raises concerns regarding the capacity of weed scientists to address research priority areas without clear private sector incentives for investment (Clancy et al. Reference Clancy, Fuglie and Heisey 2016 ). Communicating these priority areas to public sector funding agencies and demonstrating how they will contribute to sustainable crop production are essential for the diverse categories that encompass our broader discipline. Moreover, using surveys such as this as guidance for training the next generation of weed scientists can help ensure flexibility in our discipline moving forward.

Acknowledgments

We express our gratitude to the anonymous survey respondents who made this study possible. We would also like to thank Stephen Young, Alan Helm, Douglas Bessette, Steven Fennimore, Anita Dille, David Erwin, George Frisvold, Patrick Tranel, Bill Johnson, Jason K. Norsworthy, Jason Ferrell, and Chauhan Bhagirath for their advice and valuable suggestions. We also appreciate the thoughtful comments and suggestions from two anonymous reviewers on previous versions of this article. No conflicts of interest have been declared. This research received no specific grant from any funding agency or the commercial or not-for-profit sectors.

Associate Editor: William Vencill, University of Georgia

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Agricultural Research Service Weed Science Research: Past, Present, and Future

Stephen L. Young, James V. Anderson, Scott R. Baerson, Joanna Bajsa-Hirschel, Dana M. Blumenthal, Chad S. Boyd, Clyde D. Boyette, Eric B. Brennan, Charles L. Cantrell, Wun S. Chao, Joanne C. Chee-Sanford, Charlie D. Clements, F. Allen Dray, Stephen O. Duke, Kayla M. Eason, Reginald S. Fletcher, Michael R. Fulcher, Brenda J. Grewell, Erik P. Hamerlynck, Robert E. Hoagland David P. Horvath, Eugene P. Law, Daniel E. Martin, Clint Mattox, Steven B. Mirsky, Patrick J. Moran, Rebecca C. Mueller, Vijay K. Nandula, Beth A. Newingham, Zhiqiang Pan, Lauren M. Porensky, Paul D. Pratt, Andrew J. Price, Brian G. Rector, Krishna N. Reddy, Roger L. Sheley, Lincoln Smith, Melissa C. Smith, Keirith A. Snyder, Matthew A. Tancos, Natalie M. West, Gregory S. Wheeler, Martin M. Williams , Julie Wolf, Carissa L. Wonkka, Alice A. Wright, Jing Xi, Lew H. Ziska Show 28 others Show less

Research output : Contribution to journal › Article › peer-review

The U.S. Department of Agriculture-Agricultural Research Service (USDA-ARS) has been a leader in weed science research covering topics ranging from the development and use of integrated weed management (IWM) tactics to basic mechanistic studies, including biotic resistance of desirable plant communities and herbicide resistance. ARS weed scientists have worked in agricultural and natural ecosystems, including agronomic and horticultural crops, pastures, forests, wild lands, aquatic habitats, wetlands, and riparian areas. Through strong partnerships with academia, state agencies, private industry, and numerous federal programs, ARS weed scientists have made contributions to discoveries in the newest fields of robotics and genetics, as well as the traditional and fundamental subjects of weed-crop competition and physiology and integration of weed control tactics and practices. Weed science at ARS is often overshadowed by other research topics; thus, few are aware of the long history of ARS weed science and its important contributions. This review is the result of a symposium held at the Weed Science Society of America's 62nd Annual Meeting in 2022 that included 10 separate presentations in a virtual Weed Science Webinar Series. The overarching themes of management tactics (IWM, biological control, and automation), basic mechanisms (competition, invasive plant genetics, and herbicide resistance), and ecosystem impacts (invasive plant spread, climate change, conservation, and restoration) represent core ARS weed science research that is dynamic and efficacious and has been a significant component of the agency's national and international efforts. This review highlights current studies and future directions that exemplify the science and collaborative relationships both within and outside ARS. Given the constraints of weeds and invasive plants on all aspects of food, feed, and fiber systems, there is an acknowledged need to face new challenges, including agriculture and natural resources sustainability, economic resilience and reliability, and societal health and well-being.

• Biological control
• climate change
• genome sequencing
• herbicide resistance
• integrated weed management
• invasive plant ecology
• machine learning

ASJC Scopus subject areas

• Agronomy and Crop Science
• Plant Science

Online availability

• 10.1017/wsc.2023.31

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• Link to publication in Scopus
• Link to the citations in Scopus

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• Futures Past Keyphrases 100%
• Past-present Keyphrases 100%
• Agricultural Research Service Keyphrases 100%
• Weed Science Keyphrases 100%
• Invasive Plants Keyphrases 42%
• Weeds Keyphrases 28%
• Management Tactics Keyphrases 28%
• Herbicide Resistance Keyphrases 28%

T1 - Agricultural Research Service Weed Science Research

T2 - Past, Present, and Future

AU - Young, Stephen L.

AU - Anderson, James V.

AU - Baerson, Scott R.

AU - Bajsa-Hirschel, Joanna

AU - Blumenthal, Dana M.

AU - Boyd, Chad S.

AU - Boyette, Clyde D.

AU - Brennan, Eric B.

AU - Cantrell, Charles L.

AU - Chao, Wun S.

AU - Chee-Sanford, Joanne C.

AU - Clements, Charlie D.

AU - Dray, F. Allen

AU - Duke, Stephen O.

AU - Eason, Kayla M.

AU - Fletcher, Reginald S.

AU - Fulcher, Michael R.

AU - Grewell, Brenda J.

AU - Hamerlynck, Erik P.

AU - Hoagland, Robert E.

AU - Horvath, David P.

AU - Law, Eugene P.

AU - Martin, Daniel E.

AU - Mattox, Clint

AU - Mirsky, Steven B.

AU - Moran, Patrick J.

AU - Mueller, Rebecca C.

AU - Nandula, Vijay K.

AU - Newingham, Beth A.

AU - Pan, Zhiqiang

AU - Porensky, Lauren M.

AU - Pratt, Paul D.

AU - Price, Andrew J.

AU - Rector, Brian G.

AU - Reddy, Krishna N.

AU - Sheley, Roger L.

AU - Smith, Lincoln

AU - Smith, Melissa C.

AU - Snyder, Keirith A.

AU - Tancos, Matthew A.

AU - West, Natalie M.

AU - Wheeler, Gregory S.

AU - Williams, Martin M.

AU - Wolf, Julie

AU - Wonkka, Carissa L.

AU - Wright, Alice A.

AU - Xi, Jing

AU - Ziska, Lew H.

N1 - Publisher Copyright: © The Author(s), 2023. Published by Cambridge University Press on behalf of the Weed Science Society of America.

PY - 2023/7/16

Y1 - 2023/7/16

N2 - The U.S. Department of Agriculture-Agricultural Research Service (USDA-ARS) has been a leader in weed science research covering topics ranging from the development and use of integrated weed management (IWM) tactics to basic mechanistic studies, including biotic resistance of desirable plant communities and herbicide resistance. ARS weed scientists have worked in agricultural and natural ecosystems, including agronomic and horticultural crops, pastures, forests, wild lands, aquatic habitats, wetlands, and riparian areas. Through strong partnerships with academia, state agencies, private industry, and numerous federal programs, ARS weed scientists have made contributions to discoveries in the newest fields of robotics and genetics, as well as the traditional and fundamental subjects of weed-crop competition and physiology and integration of weed control tactics and practices. Weed science at ARS is often overshadowed by other research topics; thus, few are aware of the long history of ARS weed science and its important contributions. This review is the result of a symposium held at the Weed Science Society of America's 62nd Annual Meeting in 2022 that included 10 separate presentations in a virtual Weed Science Webinar Series. The overarching themes of management tactics (IWM, biological control, and automation), basic mechanisms (competition, invasive plant genetics, and herbicide resistance), and ecosystem impacts (invasive plant spread, climate change, conservation, and restoration) represent core ARS weed science research that is dynamic and efficacious and has been a significant component of the agency's national and international efforts. This review highlights current studies and future directions that exemplify the science and collaborative relationships both within and outside ARS. Given the constraints of weeds and invasive plants on all aspects of food, feed, and fiber systems, there is an acknowledged need to face new challenges, including agriculture and natural resources sustainability, economic resilience and reliability, and societal health and well-being.

AB - The U.S. Department of Agriculture-Agricultural Research Service (USDA-ARS) has been a leader in weed science research covering topics ranging from the development and use of integrated weed management (IWM) tactics to basic mechanistic studies, including biotic resistance of desirable plant communities and herbicide resistance. ARS weed scientists have worked in agricultural and natural ecosystems, including agronomic and horticultural crops, pastures, forests, wild lands, aquatic habitats, wetlands, and riparian areas. Through strong partnerships with academia, state agencies, private industry, and numerous federal programs, ARS weed scientists have made contributions to discoveries in the newest fields of robotics and genetics, as well as the traditional and fundamental subjects of weed-crop competition and physiology and integration of weed control tactics and practices. Weed science at ARS is often overshadowed by other research topics; thus, few are aware of the long history of ARS weed science and its important contributions. This review is the result of a symposium held at the Weed Science Society of America's 62nd Annual Meeting in 2022 that included 10 separate presentations in a virtual Weed Science Webinar Series. The overarching themes of management tactics (IWM, biological control, and automation), basic mechanisms (competition, invasive plant genetics, and herbicide resistance), and ecosystem impacts (invasive plant spread, climate change, conservation, and restoration) represent core ARS weed science research that is dynamic and efficacious and has been a significant component of the agency's national and international efforts. This review highlights current studies and future directions that exemplify the science and collaborative relationships both within and outside ARS. Given the constraints of weeds and invasive plants on all aspects of food, feed, and fiber systems, there is an acknowledged need to face new challenges, including agriculture and natural resources sustainability, economic resilience and reliability, and societal health and well-being.

KW - Biological control

KW - climate change

KW - genome sequencing

KW - herbicide resistance

KW - integrated weed management

KW - invasive plant ecology

KW - machine learning

KW - robotics

UR - http://www.scopus.com/inward/record.url?scp=85169052050&partnerID=8YFLogxK

UR - http://www.scopus.com/inward/citedby.url?scp=85169052050&partnerID=8YFLogxK

U2 - 10.1017/wsc.2023.31

DO - 10.1017/wsc.2023.31

M3 - Article

AN - SCOPUS:85169052050

SN - 0043-1745

JO - Weed Science

JF - Weed Science

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Reviewing research priorities in weed ecology, evolution and management: a horizon scan

Associated data.

Table S1. The 124 pre‐submitted research questions that address fundamental and applied issues in weed ecology, evolution and management

Weedy plants pose a major threat to food security, biodiversity, ecosystem services and consequently to human health and wellbeing. However, many currently used weed management approaches are increasingly unsustainable. To address this knowledge and practice gap, in June 2014, 35 weed and invasion ecologists, weed scientists, evolutionary biologists and social scientists convened a workshop to explore current and future perspectives and approaches in weed ecology and management. A horizon scanning exercise ranked a list of 124 pre‐submitted questions to identify a priority list of 30 questions. These questions are discussed under seven themed headings that represent areas for renewed and emerging focus for the disciplines of weed research and practice. The themed areas considered the need for transdisciplinarity, increased adoption of integrated weed management and agroecological approaches, better understanding of weed evolution, climate change, weed invasiveness and finally, disciplinary challenges for weed science. Almost all the challenges identified rested on the need for continued efforts to diversify and integrate agroecological, socio‐economic and technological approaches in weed management. These challenges are not newly conceived, though their continued prominence as research priorities highlights an ongoing intransigence that must be addressed through a more system‐oriented and transdisciplinary research agenda that seeks an embedded integration of public and private research approaches. This horizon scanning exercise thus set out the building blocks needed for future weed management research and practice; however, the challenge ahead is to identify effective ways in which sufficient research and implementation efforts can be directed towards these needs.

Introduction

Weeds are defined here as any plants that have negative socio‐economic and/or environmental impacts, threaten global food security, biodiversity, ecosystem services and human health. Crop yield losses to weed competition have been estimated as 9% globally (Oerke, 2006 ), leading to estimates of annual economic losses of $27 billion and $3.2 billion, in the USA (Pimentel et al ., 2005 ) and UK (Pimentel et al ., 2001 ) respectively. In natural ecosystems, non‐native weeds have serious negative impacts on biodiversity and ecosystem functioning (Ehrenfeld, 2010 ; Simberloff et al ., 2013 ). Invasive weeds may also result in serious consequences to human health through, for example, increased loads of allergenic pollen (Hamaoui‐Laguel et al ., 2015 ). Impacts of weeds in current systems are likely to get worse rather than better, due to increased long‐distance trade, climate change, altered disturbance patterns, herbicide resistance and other factors, making improvements in weed management ever more urgent.

The global human population is projected to increase to 9 billion people by 2050, with conservative estimates suggesting an associated increase in food consumption and demand of 50% (Royal Society of London, 2009 ). This demand will need to be satisfied without increasing the global area of agricultural land, with fewer inputs and with a lower environmental impact, a concept described as ‘sustainable intensification’ (Royal Society of London, 2009 ; Tilman et al ., 2011 ; Struik & Kuyper, 2017 ). For sustainable intensification to close the gap between theoretically attainable and realised crop yields (the ‘yield gap’, van Ittersum et al ., 2013 ) whilst reducing negative environmental impacts, weed management strategies will require continued innovation, particularly considering the evolution of resistance to existing control measures (Godfray et al ., 2010 ) and the continued introduction and spread of novel weeds or weedy traits (Driscoll et al ., 2014 ). Climate and environmental change may also alter competitive interactions between agricultural weeds and crops, meaning that, over time, the nature and distribution of the most yield‐limiting weeds may change (Fuhrer, 2003 ). Additionally, the ecological impacts of invasive weeds are profound (Vilà et al ., 2011 ) and are expected to worsen with global environmental change (Bradley et al ., 2010 ). Existing management strategies for invasive plants are often proving ineffective at producing long‐term benefits (Pearson et al ., 2016 ).

The converging challenges of global food security, climate change, environmental degradation, escalating rates of plant invasion, evolution of resistance to herbicides and the systemic failure to adopt integrated weed management (IWM) pose a stark challenge to the fields of weed ecology and management. Current trends suggest that weed problems will worsen in the next 10–20 years, becoming an even more intractable barrier in efforts towards the sustainable intensification of agricultural production and the preservation of natural habitats. It is critical that future efforts be more coordinated, collaborative, innovative and conducive to adoption. These challenges provide a timely opportunity to readdress the question ‘what are the future research priorities in weed ecology and management?’.

In June 2014, a group of 35 scientists engaged in various aspects of weed research and practice, spanning agricultural and invasive weeds, genetics and evolutionary biology, ecology, weed management and social science assembled at a workshop in Benasque, Spain, to consider future dimensions in weed biology and management. To facilitate those discussions, a horizon scanning exercise was performed (Sutherland et al ., 2006 ; Grierson et al ., 2011 ; Ricciardi et al ., 2017 ). Before the workshop, invitees were asked to submit three to five ‘key questions’ that they considered to be major challenges for the discipline of weed ecology, evolution and management in agricultural and invaded natural systems over the next five to ten years. Through individual reflection and facilitated group discussion, the 124 questions submitted were ranked in importance. The top 30 ranked questions are presented here (Table  1 ) and form the basis of the commentary that follows. A full list of the submitted questions is included as supporting information, together with further details of the ranking exercise.

The 30 top‐ranked current and future research questions in weed ecology and management. Questions are grouped and discussed under seven research themes

Horizon scanning priorities and opportunities in weed ecology and management

In summarising the top‐ranked research questions (Table  1 ), seven salient themes were identified, each of which is discussed below.

Transdisciplinary research

The two top ‐ ranked questions (and two others) placed a strong emphasis on the need for broadening research horizons, such that multistakeholder approaches to tackle weed problems and their management are fostered. Within these transdisciplinary frameworks (Lang et al ., 2012 ; Jordan et al ., 2016 ), weed ecologists, weed scientists, land managers, farmers, economists and social scientists should work together with agricultural, industrial and governmental stakeholders with an interest in tackling intractable weed problems (Graham, 2013 ; Ervin & Jussaume, 2014 ). Narrow framing of weed problems is less likely to engage the full range of stakeholders needed to devise and implement innovative solutions, and weed research must be considered in the context of wider efforts towards the design of sustainable farming systems. Continued technological innovation will be a key requirement for developing, testing and promoting sustainable weed management strategies, though a better balance is required between public and private sector research, development and funding for weed science. Whereas the public sector has been more inclined to focus on a range of systems‐based approaches, the private sector has continued to seek to develop ‘patentable’, technological solutions. Transdisciplinary science can serve to facilitate public–private partnerships that ensure that the most promising technological advances are deployed in systems that preserve their efficacy, maintain weed management and agroecosystem diversity and limit the potential undesirable environmental impacts of weed management.

Adoption of integrated weed management

Two questions (ranked 6 and 21) identified the importance of continued efforts to increase, understand and incentivise adoption of IWM approaches (see Liebman et al ., 2016 ). Underlying reasons for this lack of adoption are multifaceted and likely reflect a continued desire for ‘simple’ technological solutions, short‐term planning horizons and a failure by researchers to demonstrate and communicate the benefits of more integrated approaches. In part, future research approaches can address these questions using transdisciplinary frameworks that enable codevelopment of weed control technology and IWM systems, socio‐economic approaches to better understand farmer decision‐making and a wider framing of weed management challenges and solutions, including through public–private collaborations.

Weeds as agroecological actors

A series of questions (ranked 5, 7, 10, 11, 17, 22) recognised the need for a greater research effort to reconcile the negative and positive impacts of weeds in agroecosystems. The interactions of weeds with other trophic levels and in relation to soil health and functioning can be important for delivering ecosystem services (Marshall et al ., 2003 ). These services can include the provision of food, shelter and habitat for natural enemies of crop pests or for pollinating insects, the maintenance of vegetation cover during non‐cropped phases of the rotation to control soil erosion and for the enhancement of soil structure and function (Navas, 2012 ). As such, weed functional diversity may play an important role in enhancing crop productivity by reducing losses due to insect pests and maintaining or enhancing soil health. Trophic interactions may also play important roles in regulating weed populations through, for example, weed seed predation (Westerman et al ., 2005 ; Franke et al ., 2009 ) and microbial degradation of viable seeds in the soil seedbank (Chee‐Sanford et al ., 2006 ; Müller‐Stöver et al ., 2016 ). Of course, weeds may also increase the negative impacts of other crop pests by acting as hosts, shelter and/or food sources for plant pathogens (Wisler & Norris, 2005 ) and herbivores. Understanding biotic interactions between weeds and organisms at other trophic levels will be important for designing weed management strategies that enhance the natural capacity for ecosystems to regulate weed and pest populations. In this way, weed management strategies must be considered in the context of multifunctional landscapes that optimise crop production and environmental integrity whilst maintaining provisioning, sustaining and cultural ecosystem services. More diverse weed floras, selected for by more diverse weed management and cropping systems, may buffer systems against dominance by one or a few aggressive, resistance‐prone species, therefore increasing systemic resilience to weeds. Indeed, evidence from the long‐term Broadbalk experiment at Rothamsted Research has identified a negative correlation between weed diversity and crop yield loss (Moss et al ., 2004 ). This observation suggests that increased weed diversity may not always have a negative impact on crop yield.

Weed evolution

Workshop participants recognised a need to better understand the nature and importance of weed adaptation that underpins the evolution of weedy traits in agricultural and invaded natural systems (ranked 3, 9, 12 and 30). We are reminded of the words of Harper ( 1956 ) that ‘Arable weeds constitute an ecological group selected and maintained in association by their fitness for existence under conditions of crop cultivation. They comprise species that have been selected by the very practices that were originally designed to suppress them’. The ability of weedy plants to rapidly adapt to novel environments and anthropogenic management has been proposed as a key facet of the ‘weed syndrome’ (Vigueira et al ., 2012 ). In agricultural systems, weed management, particularly the use of herbicides, exerts extreme selection pressure, and the capacity for weeds to rapidly evolve resistance to herbicides has been demonstrated extensively (Powles & Yu, 2010 ). Further, one of our questions acknowledged the need to also understand adaptive potential in relation to cultural weed management. In invasion ecology (see below), it is suggested that the success of invasive plants may be due, at least in part, to their ability to rapidly adapt to novel environments (Prentis et al ., 2008 ). In the light of these phenomena, it has been proposed that weedy plants provide excellent model systems for studying contemporary adaptation in plants (Baucom & Holt, 2009 ; Neve et al ., 2009 ; Vigueira et al ., 2012 ). The extent to which phenotypic plasticity versus genetic variation is implicated in this adaptive potential is also an open question and, added to this, there is increasing interest in the role of epigenetic regulation in rapid evolution in plants (Becker & Weigel, 2012 ). In practical terms, answering these questions will be important for understanding how weed populations and communities respond to management strategies that aim to disrupt contemporary evolution through the design of heterogeneous landscapes, crop rotations and through the optimisation and adoption of IWM strategies.

Invasiveness

Important questions relating to a better understanding of weed invasiveness (ranked 13, 23, 27), drew on themes developed in the two preceding sections. To what extent are invasions facilitated (or hindered) by interactions (or lack of) across trophic levels? What is the importance of post‐invasion evolution to invasion success? Invasion of an ecosystem by one species may be facilitated by native species or by previous invaders with sequential, facilitated invasions potentially leading to ‘invasional meltdown’ (Simberloff & von Holle, 1999 ). The success of invading species may be due to release from natural enemies, present in their native habitat, but absent in the invaded range (Williamson, 1996 ; Mitchell & Power, 2003 ), though reports of pathogen accumulation and subsequent population decline of invasive plant species after initial establishment have also been noted (Flory & Clay, 2013 ). Interactions between plants and soil microbes can also contribute to invasiveness (Klironomos, 2002 ; Callaway et al ., 2004 ). Likewise, the failure of some species to invade may be due to the absence of mutualistic organisms in environments into which they are introduced (Richardson et al ., 2000 ).

Climate change

Global climate change (ranked 4, 8, 16, 18, 26) will impact the dispersal of weedy plants, the invasibility of agricultural and natural habitats and competitive interactions. Climate change is clearly recognised as a major driver for increased rates of plant invasion (Diez et al ., 2012 ), and in agricultural situations, the geographical range over which weeds are highly competitive versus crops (the ‘damage niche’) may shift in response to altered cultivation practices associated with climate change (McDonald et al ., 2009 ; Stratonovitch et al ., 2012 ). The ability to better predict the introduction pathways and invasive potential of plants under climate change is critically important, so that those species likely to have the greatest negative environmental and socio‐economic impacts can be identified and anticipated. The ability to predict those plant traits that will be most impacted by climate change will help to understand which species will become more invasive under climate change. However, it is also important to recognise that a changing climate may result in wider ecosystem change and, in this context, the concept of what defines ‘native’ and ‘invasive’ species may also change (Webber & Scott, 2012 ).

Weed science

A final set of questions (ranked 14, 24, 25, 29) raised several important issues relating to the future scope, definition, ambitions and approaches for the discipline of weed science (biology, ecology, management). A narrowing of focus was highlighted, invoking arguments about a ‘critical juncture’ for the discipline (Mortensen et al ., 2012 ) and acknowledging that the advent and unprecedented adoption of herbicides for weed management have resulted in a discipline that has approached weed science from an increasingly narrow plant physiological versus a broader plant ecological perspective (Neve et al ., 2014 ). Two questions addressed a similar issue about the need for our discipline to find a better balance between ‘applied’ and ‘fundamental’ science, and there was a consensus that much weed research ‘fell between the cracks’ in this regard. This may reflect a general perception that the study of weeds, even when focused on fundamental questions of weed biology, is an overtly ‘applied’ science, sometimes limiting access to more basic science funding. This ‘problem’ is less evident in plant invasion biology where scientific questions are successfully framed in the wider context of community assembly and ecosystem functioning and where the study of plant invasions is recognised as a means to address fundamental questions in plant ecology. In the future, the discipline of agricultural weed science should recognise and rise to the challenge of framing fundamental questions in plant ecology and evolution around the study of weeds in agroecosystems. Presenting weed science in transdisciplinary terms will similarly open up opportunities for those focused on the biology and management of weeds to expand the scope and focus of the discipline. These endeavours will facilitate wider efforts to attract the best scholars into the weed science discipline, with associated benefits in terms of raising the profile of the discipline, conducting fundamental science with ‘impact’ and addressing many of the challenges and opportunities highlighted by this horizon scanning exercise.

The overarching question that we have sought to address is how can we achieve weed management that is effective, economical, minimises negative environmental consequences and is robust to weed adaptation and future environmental change? From the preceding discussion, a single, unifying ‘meta‐theme’ has emerged: the need for more‐diversified agroecosystems to tackle intractable weed problems in ways that are economically and environmentally sustainable. Indeed, we observe that most of the research themes outlined above are pertinent to diversified agroecosystems and are largely of uncertain relevance in low‐diversity agroecosystems. The severe problems of weed management in low‐diversity systems are clear, and we call for a shift to focusing on critical scientific questions about weed management in more‐diversified systems. This effort will add impetus to wider efforts to enhance diversification in agriculture, which remains highly challenging in the face of many factors that favour more simplified cropping systems, production technologies and market drivers, even though such simplified systems now show limited sustainability.

Transdisciplinary approaches (Jordan et al ., 2016 ) acknowledge the social, economic and political dimensions of weed management, engaging multiple stakeholders in the cocreation and codesign of IWM systems, overcoming potential barriers to subsequent adoption (Llewellyn, 2007 ; Wilson et al ., 2009 ; Liebman et al ., 2016 ) and ensuring a closer integration between public and private sector perspectives and drivers in weed management. More system‐based approaches to weed management can help to address some of the tensions and trade‐offs between economic, environmental and societal objectives, recognising the need for a closer integration between ‘technological‐’ and ‘ agroecological ’‐based solutions (Jordan & Davis, 2015 ). In this sense, we see opportunity and potential in drawing parallels with global healthcare challenges. Indeed, the concept of ‘one health’ in human and animal healthcare demonstrates an emerging consensus for a more holistic approach (Hueston et al ., 2013 ) that recognises a strong environmental component and ecological interactions in the epidemiology of human and animal disease.

A more systemic, diversity‐oriented focus acknowledges that weeds can perform positive as well as negative roles in agroecosystems (Marshall et al ., 2003 ; Navas, 2012 ), interacting with species at other trophic levels to deliver provisioning and regulating ecosystem services. Similar arguments can apply in natural systems invaded by non‐native weedy plants where there needs to be a clearer focus on those species which have the greatest ecological impact, accepting that some invasive species have few long‐term negative impacts. It is critical to recognise that these agroecological approaches do not envision cropping systems that tolerate large populations of competitive weeds. Instead, we argue that more diverse management systems that support and maintain a higher level of weed diversity will select against one or a few dominant, competitive species that typically come to dominate low‐diversity management systems. Whilst the notion of tolerating a more diverse weed flora may remain anathema to many, we point to the extensive evidence that current technological approaches have, with few exceptions, led to the dominance of one or a few, highly competitive, herbicide resistance‐prone species (see Délye et al ., 2010 ; Ward et al ., 2013 ; Owen et al ., 2014 ). The move towards more‐diversified weed management is wholly consistent with the need to better understand and manage weed evolution . Low‐diversity weed management systems with heavy reliance on herbicides and without sufficient crop rotation impose strong directional selection for weedy traits, and a central tenet of IWM must be to diversify selection pressures to avoid the dominance of agricultural fields by one or a few highly adapted species, whether they be native or invasive in origin.

Global and regional climate change will continue to drive changes in plant species distributions and competitiveness, likely increasing the invasiveness of some species (Dukes & Mooney, 1999 ) and leading to new weed problems in agricultural and natural ecosystems. These challenges similarly call for broadening horizons in weed management to better understand the ecological and evolutionary drivers of invasion under climate change. Designing weed management systems that are more resilient to future invasions requires a similar focus on transdisciplinarity that acknowledges the social, economic and political dimensions of weed problems and the need for systemic ecological approaches that limit the invasion and ongoing adaptation of new weed species. As a direct outcome of our Spanish workshop, we organised a follow‐up meeting on transdisciplinarity in weed research in Canada in 2016. For this, we brought in a much wider range of disciplines and participants, including social scientists, extension scientists and local landowners. This workshop focused on establishing a common language and approach to integration of social and weed science to achieve the goals of effective long‐term weed solutions.

These challenges and their underlying research and philosophical questions present an opportunity for reinvention in weed/invasion science to broaden the scope of the discipline and, in doing so, to address emerging concerns about a disconnection between ‘basic’ and ‘applied’ science and the need to continue to attract the best scholars into the discipline. There is a healthy, ongoing debate about the future of the weed science discipline (Mortensen et al ., 2012 ; Ward et al ., 2014 ; Barrett et al ., 2017 ; Harker et al ., 2017 ). We should embrace that debate, avoiding fractious divisions that threaten to promulgate a false dichotomy between ‘technological’ and ‘agroecological’ approaches to weed management. The design of sustainable weed management systems that are robust to weed adaptation, weed invasion and future climate change and that place weed science in a broader context of sustainable intensification requires system‐based approaches that integrate technological and agroecological principles in diversified agroecosystems.

Supporting information

Data S1. Materials and methods.

Acknowledgements

The workshop organisers would like to express sincere gratitude to the University of Lleida, Spain, for technical support and facilities. The European Weed Research Society generously contributed a grant to the workshop organisers to support attendance of early career researchers (B.B., D.L., J.N., L.H., M.R., M.S., S.H.). P.N. acknowledges the financial support of the Biotechnology and Biological Sciences Research Council (BB/L001489/1 and BBS/OS/CP/000001). J.N.B. acknowledges the USDA Controlling weedy and Invasive Plants program (2013‐67013‐21306). S.G. received financial support from Meat and Livestock Australia for attendance at the workshop. D.Z. was supported by an NERC Fellowship (NE/I022027/1). B.B. received support from Sociedad Espanola de Malherbologia (SEMh). M.C. was awarded a Grains Research and Development Corporation of Australia Travel Award.

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Sosnoskie Lab: Research topics

New specialty crop herbicides.

One of Lynn's research focuses is identifying new herbicide active ingredients for use in specialty crops. Compared to corn, soybean and cotton, commercial fruits and vegetables are grown on very few acres in the United States. Additionally, these crops are often sensitive to many herbicides/herbicide modes of action. Combined, these factors can limit the number of registered chemicals available for weed control in non-agronomic systems. In partnership with commodity groups, agricultural manufacturers, and the IR-4 Project, Sosnoskie’s lab is screening novel products for potential labeling.

Herbicide resistance

Repeated use of some herbicides over time and space can lead to intense pressure that selects for weed biotypes able to tolerate various herbicide chemistries. So another focus area of Lynn's research is confirming and describing herbicide resistance in weed species that have grown increasingly difficult to control.

This includes glyphosate resistance and resistance to the ALS-inhibiting chemistries in Palmer amaranth ( Amaranthus palmeri ) and waterhemp ( Amaranthus tuberculatus ). It also includes resistance to paraquat in horseweed ( Erigeron canadensis ).

Other weed species-herbicide combinations of concern and investigation include common lambsquarters ( Chenopodium album )/bentazon, Powell amaranth ( Amaranthus powellii )/PPO-inhibiting herbicides, and common ragweed ( Ambrosia artemisiifolia )/clopyralid.

New weed control tools

While herbicides are an important component of weed management, they are not a silver bullet. Sustainable programs must investigate other tools and technologies for controlling unwanted vegetation. Lynn’s lab is also exploring non-chemical strategies for weed suppression including cover crops and mulches and vision-guided and electric weeders.

Research Topics

Plant and insect biodiversity can contribute to crucial ecosystem services in agricultural landscapes, including pollination and biological control.

The goal of our research is to inform the development of integrated, multi-tactical weed and crop management strategies that are both economically and ecologically sustainable.

Our lab’s interest in weedy plants in agroecosystems is paralleled by our work on invasive species in forest systems. We are studying population dynamics and spatial distributions of forest invasive species including Microstegium vimieum (Japanese stiltgrass).

We are interested in the pattern and process of dispersal and how dispersal impacts management of invasive weed species. Currently several projects in the lab examine seed transported along roads and in the atmosphere.

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Weed Research is an international peer-reviewed journal that publishes topical and innovative papers on all aspects of weeds, defined as plants that impact adversely on economic, aesthetic or environmental aspects of any system. Topics include: Weed biology and control, Herbicides, Invasive plant species in all environments, Population and spatial biology, Modelling, Genetics, Diversity and Parasites. The journal welcomes submissions on work carried out in any part of the world. In addition to research papers, the journal seeks review articles and shorter insights papers covering personal views, new methods and breaking news in weed science.

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Introduction

What herbicides will we be using in 2050, traditional herbicide chemistries, new herbicide targets and biopesticides, rna interference herbicides and genetic engineering, precision agriculture and robotics, the need for precision, co-robotics, the symbiosis among man, machine, and crop plants, beginning of the robotic weeding era, harnessing biology for weed management, enhancing crops for improved competitive ability, biological control of weeds, information technology for extension, communication and computer power, trends in future information transfer, training the next generation of weed scientists, conclusions.

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The discipline of weed science is at a critical juncture. Decades of efficient chemical weed control have led to a rise in the number of herbicide-resistant weed populations, with few new herbicides with unique modes of action to counter this trend and often no economical alternatives to herbicides in large-acreage crops. At the same time, the world population is swelling, necessitating increased food production to feed an anticipated 9 billion people by the year 2050. Here, we consider these challenges along with emerging trends in technology and innovation that offer hope of providing sustainable weed management into the future. The emergence of natural product leads in discovery of new herbicides and biopesticides suggests that new modes of action can be discovered, while genetic engineering provides additional options for manipulating herbicide selectivity and creating entirely novel approaches to weed management. Advances in understanding plant pathogen interactions will contribute to developing new biological control agents, and insights into plant-plant interactions suggest that crops can be improved by manipulating their response to competition. Revolutions in computing power and automation have led to a nascent industry built on using machine vision and global positioning system information to distinguish weeds from crops and deliver precision weed control. These technologies open multiple possibilities for efficient weed management, whether through chemical or mechanical mechanisms. Information is also needed by growers to make good decisions, and will be delivered with unprecedented efficiency and specificity, potentially revolutionizing aspects of extension work. We consider that meeting the weed management needs of agriculture by 2050 and beyond is a challenge that requires commitment by funding agencies, researchers, and students to translate new technologies into durable weed management solutions. Integrating old and new weed management technologies into more diverse weed management systems based on a better understanding of weed biology and ecology can provide integrated weed management and resistance management strategies that will be more sustainable than the technologies that are now failing.

The year 2050 is a landmark date as perceived by government, industry, and the media. Around that time, the world's human population is expected to peak at 9 billion, straining global capacity to provide sufficient energy, freshwater, and food ( Figure 1A ) ( Alexandratos and Bruinsma 2012 ). Current crop production levels are not adequate to feed the projected population, and meeting this anticipated demand is viewed as a major challenge for humanity. The burden of meeting these needs will be exacerbated by climate change, loss of water resources, and reductions in arable land due to multiple causes. Weed management is essential for agricultural production and management of landscapes and the environment and will play an important role in determining whether we meet future food production requirements.

This article is the result of a symposium held at the 2016 WSSA conference in San Juan, Puerto Rico. The objective of the symposium was to consider the long-term future of weed control and the knowledge needed to frame a sustainable system for weed management. Symposium speakers were asked to extrapolate from current and emerging technologies to imagine what weed management must look like in 2050 if agriculture is to realize the yield increases required to sustain the world's future population. Weeds are a persistent problem, and the continuing rise in numbers of herbicide-resistant biotypes reinforces the lesson that weed control technology must constantly advance to stay ahead of weed evolution and adaptation. Fortunately, the rapid pace of technological advancement and new breakthroughs in the life sciences offer the potential for new and improved methods of weed management.

Trends discussed in this article. (A) The growing world human population and the agricultural production needed to meet growing demand. Data and projections based on World Bank estimates. (B) Rise in herbicide-resistant weed biotypes and leveling off of new herbicide sites of action discovered. Historical data based on Heap ( 2017 ). Projections of herbicide resistance assume continued patterns of herbicide use, but eventual leveling off is expected due to reduced use of some herbicides and saturation of resistance in weed populations. Projection of new herbicide sites of action assumes breakthroughs leading to four new chemistries over the next 35yr. (C) Broad trends in computational power, communication networking, and biological manipulation. Lines are representative of rising trajectories, but otherwise only intended to promote discussion within the context of the article. Gray vertical line indicates the present year in all graphs.

The 32 yr until 2050 provide a relatively long time frame in which many things are possible, some of which we can imagine and many we cannot. This is both an opportunity and a challenge. Taking the optimistic viewpoint that innovation in crop genetics will be sufficient to meet the yield requirements of a world population of around 9 billion, the challenge of weed control will remain indefinitely. Weeds will continue to evolve and persist, and we should take this as a challenge to find truly sustainable solutions to weed management.

Recent reviews that look to the future of weed management provide excellent summaries of current strengths of, gaps in, and needs of weed science (e.g., Bajwa et al. 2017 ; Shaner and Beckie 2014 ). Various authors have advocated improved framing of research questions to reveal fundamental principles of weed ecology and evolution ( Justine et al. 2012 ; Ward et al. 2014 ), increasing the use of integrated weed management approaches ( Mortensen et al. 2012 ), better integrating basic knowledge with applied weed science ( Moss 2008 ), and/or seizing on new research opportunities ( Fernandez-Quintanilla et al. 2008 ). We generally agree with these analyses and recommendations, but here we offer a different perspective to project how weed control will be conducted in the relatively distant future.

This exercise is intended to focus on weed management technologies that may change substantially over the next decades. Although we do not directly address weed biology, we expect the same advances in science and information processing that contribute to new weed management will also foster a revolution in understanding plant growth and development, responses to stress, and environmental interactions. Indeed, understanding of weed biology and ecology is integral to sustainable weed management, as weed populations adapt and evolve in response to new selective pressures. A priority on funding and training in these areas is reflected in our recommendations.

From the early 1950s until the early 1980s, a new herbicide mechanism of action (MOA) was commercialized every 2.5 to 3yr ( Figure 1B ) ( Duke 2012 ). However, no new MOAs have been introduced since the 1980s. And although one major company has stated that they are developing a broad-spectrum herbicide with a new MOA ( Bomgardner 2016 ), the relentless linear increase in weeds with evolved herbicide resistance since the mid-1970s ( Heap 2017 ) has created a great need for herbicides with new MOAs. Even new herbicides with old MOAs would be welcome (assuming they have no cross-resistance to cases of evolved resistance), but there has even been a decrease in the introduction of new herbicides with old MOAs ( Jeschke 2016 ). The lack of any new MOAs since the 1980s has been surprising, as normal diminishing returns would suggest discovery of at least a few new MOAs. The increase in evolved herbicide resistance, coupled with the lack of new MOAs threatens to make almost all existing herbicides unusable by 2050.

The lack of new MOAs and slowing of the herbicide discovery pipeline is probably due to several factors, including drastic consolidations of the pesticide industry, a substantial devaluation of the non-glyphosate herbicide market after glyphosate-resistant crops were introduced, more stringent regulatory requirements for new products (much greater cost to get a new product to market), and diminishing returns of discovery approaches. Use of combinatorial chemistry to inexpensively produce vast numbers of compounds for testing in high-throughput evaluations has not broken the bottleneck. In general, new herbicides with old MOAs and new transgenic crops that are resistant to old herbicides (e.g., 2,4-D and dicamba) are only short-term solutions to some existing weed problems, because resistance already exists to these herbicides.

Use of negative cross-resistance, the enhanced sensitivity to a herbicide from the herbicide class to which resistance has evolved, has the potential to prolong the use of some of our old herbicides. An example of negative cross-resistance is the mutation in a hydrilla [ Hydrilla verticillata (L. f.) Royle] phytoene desaturase (PDS) gene (Arg-304 conversion to Thr) that provides 52-fold resistance to norflurazon but renders the mutant PDS 5-fold more sensitive to diflufenican ( Arias et al. 2006 ). There are other examples of negative cross-resistance with herbicides with other MOAs such as photosystem II inhibitors ( Fuerst et al. 1986 ). Thus, the herbicide to which there is negative cross-resistance can be either mixed or alternated with the herbicide to which there is resistance to prevent and/or remove mutant plants. This strategy has not yet been used, but it could be helpful in the future to prolong the use of older herbicides.

The future of chemical control depends on the discovery of herbicides with new MOAs, but this raises the question of whether novel good herbicide target sites even exist. First, not every enzyme in a metabolic pathway is a good herbicide target. For example, even though 5-enolpyruvylshikimate-3-phosphate synthase and acetolactate synthase of the shikimate and branched-chain amino acid pathways, respectively, are excellent herbicide targets, good inhibitors of other enzymes of these pathways are too weakly herbicidal to be commercialized. A particular enzyme of a pathway may not be a good herbicide target if too much of it must be inhibited to cause plant death, if it is a relatively high abundance protein, or if there is more than one enzymatic path to the product. Thus, only a small fraction of potential herbicide targets are viable.

There are more than the 25 or so commercial herbicide target sites that are currently used ( WSSA 2017 ), and research with natural phytotoxins has demonstrated several additional novel potential herbicide target sites ( Dayan and Duke 2014 ; EvansRoberts et al. 2016; Venturelli et al. 2015 ). But, in most of these cases, the natural herbicide is too expensive, too toxic, or lacking appropriate physicochemical properties (e.g., uptake and translocation) to be a good herbicide. Nevertheless, these compounds can point the way to discovery of new target sites (i.e., new MOAs) that can be the focus of in vitro screening of less expensive and/or toxic compounds with better physicochemical properties.

One promising direction is the discovery and development of novel herbicides based on natural products that are by-products of microorganisms or extracts of plants. Only a small fraction of the world's microbial and plant biodiversity has been screened for herbicidal activity. We know that interesting herbicidal compounds with novel mechanisms of action have been discovered, and some compounds have been very successful commercial herbicides (e.g., glufosinate based on phosphinothricin, a breakdown product of bialaphos discovered from Streptomyces viridochromogenes and S. hygroscopicus by researchers in Japan). One company, Marrone Bio Innovations, has screened water extracts from approximately 15,000 microorganisms (bacteria, fungi, and actinomycetes) and 350 plant extracts and found several novel herbicidal compounds with novel modes of action (P Marrone, personal communication). Some microbial strains and a plant extract are in development at Marrone Bio Innovations and show promise as cost-effective commercial herbicides, but based on success rates, it is more technically challenging to develop a cost-effective and broad-spectrum bioherbicide than a biofungicide, bioinsecticide, or bionematicide. In the 1980s and 1990s many companies had natural product-screening discovery efforts, but the advent of glyphosate-resistant crops led to the dismantling of these operations. Today's molecular and other tools allow much more targeted and informed screening through genomics and metabolomics.

A potential new technology is the use of RNA to silence key weed genes through the process of RNA interference (RNAi), leading to either enhanced weed susceptibility to herbicides or outright death of the weed. Applied as a spray, RNA has great potential for weed management, because sequences can be designed to selectively target a specific weed species or a group of related weed species. Presumably, targets of current herbicide chemistries could be inhibited, but there would be no cross-resistance with traditional herbicides, because RNAi works through a different mechanism. Potential new targets could also be identified.

Hurdles blocking the commercial implementation of RNAi herbicides include technical problems such as formulating RNA to achieve efficient uptake into the target plant as a sprayed product. Another challenge is the development of methods for economical large-scale production of RNAs, although the cost of this is being dramatically reduced. In addition, it is not known how fast weeds will develop resistance to RNAi herbicides. From a regulatory perspective, it is not clear how long it would take to register a new herbicide based on this technology, and the opposition from consumer groups is uncertain. Unfortunately, there are no peer-reviewed research articles on the topic of sprayable RNAi for weed management, so we only have conference reports from one major company indicating that substantial effort is being put into developing this technology ( Sammons et al. 2015 ).

Other novel approaches to developing herbicides could be enabled by genetic engineering. For example, phosphite was proposed as an herbicide many years ago, but toxicity to crops was an issue (e.g., Rothbaum and Baillie 1964 ). Engineering phosphite metabolism into crops so that they can transform it to phosphate can both eliminate the need to use phosphate fertilizers and kill weeds ( López-Arredondo and Herrera-Estrella 2012 ). Furthermore, phosphite is both toxic to some plant pathogens and induces plant defense systems against pathogens ( Pinto et al. 2012 ; Saindrenan et al. 1988 ). The continuing decline of viable herbicides caused by increases in weed resistance will make such innovative approaches more attractive.

A revolutionary approach to suppressing pest populations is the use of “gene-drive” technology ( Leftwich et al. 2016 ). Although mechanisms vary, the concept involves a genetic element that is passed on to progeny at a rate greater than the 50% expected from Mendelian inheritance. While the phenomenon has been known for years, the emergence of the CRISPR/ Cas9 (clustered regularly interspaced short palindromic repeats/ CRISPR-associated protein 9) genetic editing system provides a simple, powerful tool for generating a gene drive (National Academies of Sciences, Engineering, and Medicine [NASEM] 2016 ). CRISPR/Cas9 is efficient in inserting targeted mutations in both alleles of an individual, resulting in a conversion from the heterozygous to the homozygous condition and transmission of a specific gene to nearly all progeny. This holds great promise, as the release of organisms containing a gene drive could—in just several generations—result in the replacement of a given gene with a version designed by humans. Perhaps the simplest and most compelling example of this is a proposal to eliminate malaria by releasing mosquitoes that carry a gene-drive version of a gene that compromises the mosquito’s ability to serve as a vector of the Plasmodium parasite ( Hammond et al. 2016 ). Similar ideas could be used to suppress weed populations, for example, by rendering herbicide-resistant populations of Palmer amaranth ( Amaranthus palmeri S. Wats.) to be once again susceptible to glyphosate, or even directly degrading the competitive advantage of an invasive species ( NASEM 2016 ). Whether this will work or not depends on many factors, such as the reproductive system of the target weed, its longevity, seed persistence, and fitness of the introduced trait.

Gene-drive technology raises many issues related to ethics and potential unintended consequences, but it represents a bold new tool with potential for managing ecosystems. Concerns surrounding its deployment might prevent this approach from ever being used on plants in the field. The technology is young, and additional research and development of risk mitigation strategies could lead to public acceptance. In any case, it exemplifies the type of breakthrough that could fundamentally change weed management in coming decades.

Weed management in specialty crops will change significantly by 2050. In addition to the trends in herbicide discovery and resistance described earlier, weed management in high-value specialty crops like vegetables, flowers, and herbs faces specific problems, such as the reluctance of herbicide registrants to list specialty crops on herbicide labels due to financial liabilities, as well as farm labor shortages and other factors that have led to increases in the cost of hand weeding ( Duke 2012 ; Fennimore and Doohan 2008 ; Taylor et al. 2012 ). These trends will likely persist into the future, as it is unlikely that the cost of herbicide development will decline, that pesticide manufacturers will be more willing to accept potential liability from herbicide injury to specialty crops, or that farm labor costs will decrease. Another factor moving the market away from traditional herbicides is the increasing demand for organic food ( USDA-ERS 2015 ). Conditions are optimal to realize dramatic improvements in robotics, machine vision, crop/weed detection (i.e., weed control automation), and solar power (efficiency, payload weight, battery life) that may form the leading edge of a technological revolution in broader weed management over the next 32 yr.

An example of how the combination of scarce labor availability and inadequate herbicide availability has led to innovation is the development of automated lettuce thinners and intelligent cultivators. The majority of lettuce in Arizona and California is direct seeded 4 to 7 cm apart in rows on raised beds 1- or 2-m wide with multiple rows per bed. Traditionally, laborers with hoes have thinned lettuce to 22- to 30-cm spacing between lettuce plants at a cost of approximately $444 ha -1 for both thinning and hand weeding ( Fennimore et al. 2014 ). However, thinning requires timely operations, and when laborers are in short supply or unavailable, alternative methods are needed for lettuce thinning. Therefore, small engineering companies have stepped in to fill the void left by the labor shortage. The automated lettuce thinners and intelligent cultivators use a camera for machine vision, positional monitoring, and an actuator that consists of a cultivator knife or solenoid-activated spray nozzle. The machinevision cameras feed information into a processor that uses an algorithm to detect the crop row (pattern recognition) and spacing between the crop plants in the row. Mosqueda et al. ( 2017 ) evaluated a lettuce thinner in five commercial fields. They found that both the automated thinner and hand thinning resulted in the same 26-cm spacing between lettuce plants, but the automated thinner had a standard deviation of 3.8 cm compared with 4.5 cm for hand thinning. The process of hand thinning and hand weeding took 29.3 h ha -1 , while machine thinning plus hand weeding reduced the time by about 36% ( Smith 2015 ).

To develop integrated approaches for commercial- scale weed control strategies, technological solutions including mechatronics (the combination of electronics and mechanical engineering), machine learning, and autonomous machines will play an important role. Technology is no stranger to weed control. Early research on the development of intelligent machines for the automation of on-farm cultural practices at a commercial scale began in the 1960s with work at the University of California-Davis and in the United Kingdom on automated machines for thinning of sugar beets (Beta vulgaris L). Over the past six decades, engineers have been working on new and improved technologies that build upon these early visions. For example, in the 1990s, research at UC Davis successfully designed, developed, and demonstrated intelligent, precision pulsed-jet spray technology in which a robotic system can apply a micro-dose of herbicide at the individual leaf (1 cm) scale to weeds in a field from a mobile platform ( Downey et al. 2004 ; Giles et al. 2004 ; Lamm et al. 2002 ; Zhang et al. 2012b ).

Advanced smart-machine technology for automatic weed control has been demonstrated in certain row crops when weed density is low; however, the proportion of weeds controlled automatically is still well below 100%, and commercial-scale applicability to all crops, weed species, and growing conditions has yet to be demonstrated (e.g., Fennimore et al. 2014 ). Currently, the most critical technological bottleneck preventing the realization of fully automatic weed control machines is the lack of a robust weed sensor that can detect and distinguish among closely related crop and weed species at rates well above 95% in the field environment. When isolated as images of individual leaves, advanced software algorithms for species identification have been developed (e.g., Leafsnap 2016 ). However, Hearn ( 2009 ) demonstrated that even when advanced leaf shape recognition algorithms were employed, only 72% of 151 different species were successfully recognized by automated machine-vision methods. In a traditional machine-vision sensing approach using leaf- or plant shape-based feature recognition, high weed levels are problematic due to the visual occlusion caused by the intermingling of weed and crop foliage ( Franz et al. 1991 ). While some commercial success has been demonstrated at early growth stages when weed densities are low and crop plants are readily distinguished from weeds by plant size and planting pattern, new approaches are needed to identify weeds under moderate to heavy weed levels and when plant size is not a reliable means of weed detection. In the immediate term, the two most promising sensing technologies for automated weed control systems are hyperspectral imaging and a systems approach based upon a crop-mapping sensor used at planting.

Hyperspectral imaging methods for weed detection are more robust under high weed densities than shape-based methods, because the method measures the reflectance spectra at each point in the image regardless of the visibility of the entire plant or distinct leaf shape. The species identity is then determined for each point by spectral feature recognition rather than by shape analysis (e.g., Slaughter et al. 2004 , 2008; Zhang and Slaughter 2011b ; Zhang et al. 2012b ). In addition to the method's robustness to partial leaf occlusion, Zhang and Slaughter (2011a) observed that the technique could reliably distinguish between closely related species (e.g., domestic tomato [ Solatium lycopersicum L.] and black nightshade [ Solanum nigrum L. ]), indicating a potential to overcome the challenge observed by Hearn ( 2009 ) in distinguishing between species with similar leaf shapes. The hyperweeding method is subject to the genotype by environment interaction effect on the spectral reflectance of each species ( Zhang et al. 2012a ). To become a commercial success, equipment manufacturers will need to develop advanced machine-learning methods that characterize the spectral reflectance features of important crop and weed species over a wide range of growing environments. Zhang et al. ( 2012a ) demonstrated that a machine-learning approach using a two-stage expert system was robust to the genotype by environment interaction effect by first employing an “environment expert” that mined expert knowledge from historical data to identify the best environmental match in prior growing seasons to the current season. Then, as a second step, it employed a “species expert” that would classify unknown plants by species using historical data from the most similar growing environment in the database to accurately classify the crop and weed plants.

A systems approach is another promising technique that could be implemented commercially in the short term to develop smart machines for automated weed control. In the systems approach concept, knowledge of the crop-plant locations at planting is mapped and retained for future use in crop-plant care tasks such as weed control. A weeding robot can then access the crop-plant map in real time later in the season, once weeds emerge, to distinguish crop plants from weeds based upon location. Several researchers have demonstrated the feasibility of mapping the location of crop plants in real time during planting using centimeter-accuracy realtime kinematics global positioning system (GPS) (e.g., Ehsani et al. 2004 ; Griepentrog et al. 2005 ; Pérez-Ruiz et al. 2012a ; Sun et al. 2010 ). An automated GPS weeding system was developed by PérezRuiz et al. ( 2012b ) that demonstrated the feasibility of accessing the GPS crop-plant location map in real time and using that knowledge to control the path of a pair of miniature robotic hoes to automatically kill weeds growing between crop plants in the row. An advantage of this technique is that it does not require knowledge of any crop or weed genotype by environment interaction affects and is readily adapted across a wide range of crop species and growing conditions. Another advantage is that physically robust centimeteraccuracy GPS equipment is already in commercial use in agriculture, and the cost of this type of technology is likely to decrease while its accuracy increases with future development and adoption.

Mechatronics and automation technologies are likely to become more effective and commercially viable as future weed control strategies and are already being used in industrialized countries in specific crops ( King 2017 ). Typically, vegetable crops like broccoli ( Brassica oleracea L. var. botrytis L.) , cabbage ( Brassica oleracea L.), field-grown flowers, herbs, lettuce ( Lactuca sativa L.), onion (Allium cepa L.), and tomato among others are hand weeded to achieve intrarow weed control ( Fennimore et al. 2014 ; Melander et al. 2015 ). Industry has responded to the need for automation of intrarow cultivators. As an example, the Robovator intrarow cultivator from Denmark is equipped with two flat-blade tines per crop row that undercut weeds at 1 to 2 cm below the soil surface. The tines are positioned in the intrarow area until they approach a crop plant, at which point the computer system opens the tines to safely pass by the crop, then closes them again on the following side ( Melander et al. 2015 ). The Robovator system is designed to detect the difference between the crop plant and weed based on the recognition of the crop row (as described earlier) and the size difference between the crop and weed. In the Robovator, each row has a camera, and images from the cameras are processed to determine the position of the crop, and then the computer signals the actuator to open and close at the proper location (Tati et al. 2016; Melander et al. 2015 ). In broccoli and lettuce, the Robovator reduced hand-weeding time by 39% and 27%, respectively, compared with the standard cultivator (Tati et al. 2016). Another exciting approach is being developed by Blue River Technology (  http://www.bluerivert.com ), a robotics company spin out from Stanford University. They already market the LettuceBot, a machine for precision thinning of lettuce, and are now releasing a technology called “See & Spray” for precision application of herbicides for weed control in cotton. Their approach uses extensive collections of plant images that enable their tractor-mounted unit to differentiate crop plants and weeds. They state that this “does not rely on spacing or color to identify weeds” to detect differences between plants. An advantage of this approach is the potential reduction in volumes of herbicides applied, especially at low weed densities, where the differences in herbicide use between precision spraying and broadcast applications can be dramatic.

Automatic weed removal technology provides a path to alternative weed control tools that is much more promising, at least for specialty crops, than the traditional herbicide development model that has dominated for the past 60 yr. There are fewer than 10 companies in the world that have the capacity to discover, develop, and register herbicides ( Jeschke 2016 ). In contrast, there are many more companies with expertise in robotics that can build automatic weed removal equipment, and development of robotic weeders is much less expensive than development of herbicides. So far, automated lettuce thinners have relied upon control of automated control of spray nozzles to precisely apply herbicides, acids, or fertilizer solutions. Automated intrarow cultivators have relied upon modified hoe blades controlled by processors ( Melander et al. 2015 ). However, there are many more weed control technologies to be explored for automation, such as lasers, sequential flaming, or spraying abrasives ( Erazo-Barradas et al. 2017 ; Forcella 2009 , 2012, 2013; Norremark et al. 2009 ). The power of automated weed control is the merger of traditional weed control technology with robotics. When automation technology, weed detection, and actuation are combined with a weed control device, the result is creation of a different and more effective tool.

Crop breeding for improved ability to compete with weeds has long been a goal for weed science. Early studies focused on identifying top-yielding cultivars when grown under intense weed pressure. Burnside ( 1972 ) tested the competitive ability of 10 soybean [ Glycine max (L.) Merr.] cultivars to season-long weed pressure. Three soybean cultivars, ‘Harosoy 63,’ ‘Amsoy,’ and ‘Corsoy,’ were identified as the most weed-competitive cultivars. No analyses, however, of why these cultivars were more productive was completed. Another study compared the weed competitiveness of three high-yielding, lodging-resistant rice ( Oryza sativa L.) cultivars with populations of barnyardgrass [ Echinochloa crus-galli (L.) Beauv.] ranging from 100 to 200 seed heads m -1 ( Smith 1974 ). Results suggested that late-maturing cultivars were more competitive, but again, there was no indication of any mechanism that may have accounted for this greater competitive ability. The competitive ability of tall wheat ( Triticum aestivum L.) cultivars over wild oat ( Avena sativa L.) was attributed to rapid dry matter accumulation per unit area during early seedling development ( Balyan et al. 1991 ). Recognizing that crop cultivar selection for weed-competitive ability was not proving successful, Korres and Proud-Williams (2002) concluded that crop density rather than cultivar selection was a better indicator of enhanced competitiveness with weeds. Finally, Watson et al. ( 2006 ) summed up their research on the weedcompetitive ability of 29 barley ( Hordeum vulgare L.) cultivars by stating, “Correlation coefficients were not strong enough to attempt reliable co-selection within a breeding program.” In summary, the search for enhanced weed-competitive crops based on morphological traits has not resulted in the knowledge required by plant breeders to reliably enhance the competitive ability of crops with weeds.

An alternative strategy is to focus research on the molecular, physiological, and morphological mechanisms of both interspecific and intraspecific competition. To accomplish this, we must understand how crop plants detect neighbors via plant communication and how this knowledge is then transferred into action through molecular, physiological, and morphological changes within the crop plant ( Ballare and Pierik 2017 ; Choe et al. 2016 ). Rajcan and Swanton (2001) suggested that early detection of neighboring weeds through changes in light quality, specifically red/far-red light ratio, would be a novel approach to understanding the mechanisms of early plant competition. This was refined into a hypothesis that early-season crop-weed competition was not driven by resource limitation but rather by changes in light quality caused by the presence of neighboring weed seedlings ( Rajcan et al. 2004 ), and has been further tested and demonstrated since ( Gal et al. 2015 ; Green-Tracewicz et al. 2011 ; Page et al. 2010 ). In the absence of direct competition for resources of light, water, and nutrients, neighboring weed seedlings can cause an accumulation of H 2 O 2 (a stress indicator) in both corn ( Zea mays L.) ( Afifi and Swanton 2012 ) and soybean tissue ( McKenzie-Gopsill et al. 2016 ). The molecular and physiological changes that occur as a result of the detection of neighboring weed seedlings may provide insights into the actual mechanism of crop yield loss.

There is also the opportunity to think of seed treatments not only for crop protection but as “gene triggers” that would enable crop plants to withstand physiological stress caused by abiotic and biotic variables. Seed treatments with neonicotinoid insecticides have been shown to enhance crop competitiveness in the presence of weeds. Thiamethoxam applied as a seed treatment was found to enhance maize seed germination and root growth ( Afifi et al. 2015a ) and to activate free radical-scavenging enzymes that reduced the accumulation of H 2 O 2 in maize seedlings emerging in the presence of aboveground neighboring weed seedlings ( Afifi et al. 2015b ). Thiamethoxam also prevented the loss of nodules when soybean seedlings were grown in the presence of neighboring weeds ( Kim et al. 2016 ). The ability to place a small amount of chemical into a seed and trigger genes that enhance stress tolerance to weeds opens up a whole new area of research for manipulating crop-weed interactions.

A prognosis of strategies that might be used for weed control in 2050 would be incomplete without including biological control of weeds and bioherbicides. Biological control is defined as the use of a natural enemy or a complex of natural enemies—biological control agents—to bring about weed suppression. The agents can be phytophagous arthropods (insects and mites), plant pathogens (fungi, bacteria, viruses, and nematodes), fish (e.g., grass carp [ Ctenopharyngodon idella ]), birds (e.g., geese ( Anserini sp. ), and other animals (e.g., sheep ( Ovis aries )). The importation and use of nonnative agents from a different part of the world to control (i.e., suppress or manage) an exotic invasive weed in its new home is termed “classical biological control.” Use of agents indigenous to a region by augmenting their population densities above normal levels to bring about weed suppression is called an “augmentation biocontrol strategy.”

The term “bioherbicides” has two meanings. First, it has been applied to a subset of biological control achieved by massproducing indigenous pathogens of weeds and applying them at higher than natural population densities to suppress susceptible weeds. In other words, it is an augmentation strategy, also known as inundative biocontrol. Second, the term is also used, broadly, according to the U.S. Environmental Protection Agency terminology to denote three types of biologically based herbicides: (1) biochemical herbicides (microbial metabolites, plant-derived compounds, and certain naturally occurring chemicals; discussed in “New Herbicide Targets and Biopesticides”); (2) microbial herbicides containing living or dead, plant-pathogenic or nonpathogenic microbes mixed in or not with their metabolites; and (3) genetically modified plants expressing pesticidal (herbicidal) substances (plant-incorporated protectants). It is anticipated that all of the above types of biologically based weed control methods will play a role by 2050, because they have the inherent advantages of relatively low cost of discovery and use, long-term benefits and sustainability, effectiveness, and environmental friendliness. Crops genetically modified to produce weed-fighting chemicals (allelochemicals) represent the least developed of these biocontrol technologies ( Duke 2003 ).

Classical biological control by arthropods and pathogens has had a long and illustrious history of practical contribution to weed control in non-crop situations. It has played an important role in different parts of the world, often with spectacular results, in bringing certain exotic invasive weeds to manageable levels, thereby providing vast savings in control costs while also mitigating environmental damage. Just a small list of examples of weeds successfully controlled by classical biological control include: control of alligatorweed [ Alternanthera philoxeroides (Mart.) Griseb.] by arthropods; common St. Johns wort ( Hypericum perforatum L.) by arthropods; creeping croftonweed [ Ageratina riparia (Regel) R. M. King & H. Rob.] and pricklypears ( Opuntia spp.) by arthropods and secondary pathogens; Port Jackson willow [ Acacia saligna (Labill.) Wendl. f.] by a pathogen; purple loosestrife ( Lythrum salicaria L.) by arthropods; and waterhyacinth [ Eichhornia crassipes (Mart.) Solms] by arthropods and secondary pathogens. For more examples and details, see Winston et al. ( 2014 ).

While classical biocontrol is a proven method to manage invasive weeds in undisturbed sites such as natural areas, forests, rangelands, certain water bodies, and wastelands, it is not suitable for controlling weeds in agricultural lands that are disturbed by management practices and cropping cycles. Nonetheless, looking forward to 2050, there is value to investment in classical biocontrol of weeds. Although specific biological control agents take a decade or more in some cases to research and deploy, the return on investment from successful cases typically lasts a very long time, providing increasing returns on investment ( McFadyen 1998 ). To reap continued future benefits, certain challenges to our ability to practice biological control need to be addressed with policy leadership at governmental levels. For example, there should be a coordinated global framework to facilitate the collecting and sharing of agents for biological control and to introduce the agents following sound, scientifically based prerelease risk assessment, safety and efficacy determination, and cost-benefit analysis.

Mass-production of microbes applied as bioherbicides to suppress weeds is a promising method of weed control, and several agents have been registered or approved for use as herbicide products in Canada, China, Japan, the Netherlands, South Africa, and the United States ( Bailey 2014 ; Stubbs and Kennedy 2012 ). Examples include Lockdown® (previously registered as Collego®), containing Colletotrichum gloeosporioides f. sp. aeschynomene to control northern jointvetch [ Aeschynomene virginica (L.) Britton, Sterns & Poggenb.]; Chontrol® (previously used as BioChon®), Chondrostereum purpureum for weedy broadleaved trees and shrubs; Hakatak®, Colletotrichum gloeosporioides f. sp. hakeae for silky hakea ( Hakea sericea Schrad. & J. C. Wendl); Stumpout®, Cylindrobasidium laeve for black and golden wattles ( Acacia mearnsii De Wild, and A. pycnantha Benth.); and SolviNix® , Tobacco mild green mosaic tobamovirus for tropical soda apple ( Solanum viarum Dunal). Although these bioherbicides, which are in the market, and those that were registered but are currently out of the market have served specific clientele needs to an extent, their overall contribution to weed control in terms of total usage has been extremely small compared with a typical chemical herbicide. This is true with agricultural as well as environmental weeds, and the reasons include the living bioherbicides’ inconsistency in performance due to uncontrollable interactions of the biotic agent, climate, weed characteristics, and some technical aspects, such as product storage conditions and half-life, formulation issues, and sometimes the need for specialized application technology. In addition, user acceptance of this largely unfamiliar technology and competition from chemical herbicides are also major factors. The narrow spectrum of these products further destines them to be niche products. Certainly, with the ever-increasing weed resistance to chemical herbicides, an effective bioherbicide against herbicide-resistant A. palmeri could still be a valuable product.

To have wider acceptance and relevance in the coming decades, the future microbial herbicides must be capable of controlling multiple rather than single weed targets. Their efficacy should be based on certain stable gene functions or metabolites that can operate independent of minor fluctuations in ambient temperature and moisture conditions in the field. In addition, in the coming decades, understanding how certain pathogens kill plant cells, tissues, or entire plants should be a goal. To this end, work must continue on the conventional search-and-screen efforts to find suitable weed-pathogen pairs to serve as models for study. For example, host-pathogen systems wherein pathogenicity is controlled by a gene-for-gene interaction could be used to study how systemic necrosis resulting in plant death is triggered and cascaded. Exciting possibilities exist for using omics methods to discover weed and pathogen genes and gene products involved in the herbicidal end result. As more knowledge is gained on plant-pathogen interactions, the use of newer molecular methods based on RNAi, small interfering RNA, and CRISPR/Cas9 will play a significant role in the discovery of newer products and methods of weed control. These newer molecular genetic approaches to weed control will be more readily employed if they are considered to be biologically based controls and are regulated as such.

Advances in computational power and information technology will have value beyond weed control technology; they will also impact how information is transferred and used in making weed control decisions. The amount and availability of information are increasing at exponential rates, making it difficult to accurately predict how information will be transferred in the year 2050 ( Figure 1C ). Currently, university and industry professionals use all forms of communication resources available to convey research findings to clientele ( Lubell et al. 2014 ). These include written publications and newsletters, telecommunicationss, office/ field visits, and multiple electronic resources including email, Facebook, Twitter, Instagram, LinkedIn, Pinterest, blogs, NetMeeting, and many more. Web search engines have become so ubiquitous and powerful that almost any information can be accessed, although the accuracy of the information may be suspect. The future holds ample opportunity to make information delivery and application more efficient and effective.

One current trend is the transition from a literate to a postliterate society. At the dawn of the 21st century it was estimated that more than 80% of adults worldwide could read and write at a minimum level. However, we are entering a postliterate era, in which the ability to read or write may no longer be necessary or common ( Lee 2013 ). The postliterate society replaces the written word with recorded sounds—CDs, audiobooks, broadcast spoken word and music through radio, pictures (e.g., jpeg)—and moving images—television, film, MPG, streaming video, video games, and virtual reality. A postliterate society might still include people who are literate, who know how to read and write, but choose not to. Almost all people in this category would be media literate, multimedia literate, visually literate, and transliterate. Postliteracy occurs when the ability to comprehend the written word decays. Between 1982 and 2007, reading declined by nearly 20% for the overall U.S. population and 30% for young adults ages 18 to 24, and currently 40 million Americans read at the lowest literacy level ( Tucker 2009 ). We spend less time reading, but the amount of pure information that we produce as a civilization continues to expand exponentially. The public appetite for electronic sounds and images seems insatiable.

There are at least four trends that may affect future information transfer relevant to weed management: wearable technology, contextualized learning, big data, and augmented learning. Wearable technology could serve to link growers to the most relevant information sources while they are in the field. This technology is currently available in many forms and may include “awareables” (wearable technology that is aware of people and their environment). Wearables include smartwatches, activity trackers, smart jewelry, head-mounted optical displays, and earbuds. Three things are required for a wearable: contact, connections, and context. Contact is about physical contact with the body that allows devices to detect what the wearer is doing. Connections to other devices are required to create a form of intelligence. While wearables are currently tethered to smartphones today, in the future they will become independent devices that can connect to the cloud. Context means wearables have the intelligence to understand the context in which users are working with a device and to tailor the data sent as a result.

Contextual learning is when information is provided in a way that individuals are able to construct meaning based on their own experiences. Examples of contextualized learning in agriculture would be buying a bag of crop seed from your seed dealer, buying a six-pack of tomatoes from your neighborhood store, or buying a pesticide from your dealer. When a credit card is used in the transaction, the supplier of the product can download to the buyer's electronic device personalized information such as planting dates or pesticide application advice based on that person's location as determined through the device’s electronic tracking feature. Information about soil type, environmental requirements, fertility, moisture, maturity, and other specific facts can be modified for that person's location.

“Big data” is a term for data sets so large or complex that traditional data-processing applications are inadequate. Data sets in agriculture are growing rapidly, in part because they are increasingly gathered by cheap and multiple information-sensing mobile devices, aerials (remote sensing), software logs, cameras, microphones, RFID readers, and wireless sensor networks. Most of these are already being used in agriculture, and their use can only be expected to grow. Accuracy in big data analysis may lead to more confident decision making, and better decisions can result in greater operational efficiency, cost reduction, and reduced risk. Challenges of big data include analysis, capture, data curation, searching, sharing, storage, transfer, visualization, querying, and information privacy.

Augmented learning is an on-demand learning technique in which the environment adapts to the learner. Learners can gain greater understanding of a topic from information provided on demand. For example, instead of focusing on memorization, the learner experiences an adaptive learning experience based on the current context. The augmented content can be dynamically tailored to the learner’s natural environment by displaying text, images, or video or transmitting audio. Most implementations of augmented learning are forms of e-learning. In desktop computing environments, the learner receives supplemental, contextual information through an on-screen pop-up window, toolbar, or sidebar. In mobile reality systems, annotations may appear on the learner's individual “heads-up display” or through headphones for audio instruction. For example, apps for Google Glasses can provide video tutorials and interactive click-throughs. This technology could be used to provide timely education on aspects of weed biology and management practices, for example, scouting of weeds could integrate weed identification with relevant information on potential yield losses, management options, and alerts about herbicide-resistant populations.

Despite the future wide availability of information in novel formats, some traditional teaching venues will likely continue. These may include county, area, and state grower meetings, field and demonstration tours, and schools and workshops where hands-on training is conducted. State weed control guides in written or electronic formats may continue to help growers consider effective weed control practices. These educational formats have not been discontinued over many decades, even though the numbers attending have decreased. What evidence is there that these sources of education will continue? These group meetings allow on-site human interaction in the form of discussion, detailed explanation, impromptu divergence of topics, and questions and answers, all of which can be limited and cumbersome in some electronic formats. Some people may always prefer to supplement electronic resources with a hard copy of a state weed guide or pertinent publications in their pickup, tractor, or office.

Lack of changing human behavior in weed control and herbicide use is a central issue that has been extensively considered in academia and industry ( Barrett et al. 2016 ; Ervin and Jussaume 2014 ; Jordan et al. 2016 ; Riemens et al. 2010 ; Simpson 2015 ). Accurate information on effective weed control strategies and herbicide use is available from many sources. The information has been delivered with such saturating penetration into mainstream agriculture that lack of knowledge is not a reason for nonacceptance. This pervasive and perennial trend of not adopting sustainable weed control practices has accelerated the evolution of herbicide-resistant weeds. All written journal articles, extension publications, print media, and educational venues use a myriad of tactics, including logic, reasoning, persuasion, objectivity, subjectivity, emotion, idealism, altruism, economics, efficiency, and fear to change human behavior. Despite the efforts and education spent on changing growers' attitudes and behavior, evidence exists that adoption is slow. Rather than prognosticate how weed management information will be transferred in the year 2050, perhaps weed science should employ the expertise of sociologists and socioeconomists to make accurate information better adopted and used.

The fundamental principles of weed science will be essential knowledge for weed science students for the foreseeable future. Herbicides will continue to be used, though perhaps in a more limited fashion, so training in herbicide chemistry, physiology, and technology must continue. Weed biology and ecology will continue to grow in importance through 2050, as insights into weed development and competitive interactions provide new options for managing weed populations. Keeping these facts and some of the other trends outlined earlier in mind, we must realize that weed science students will need more diverse training to be able to adapt to new employment opportunities. In Table 1 we suggest research and training areas that are needed if weed management is going to keep pace with weed evolution.

In terms of employment for weed science graduates, we foresee that opportunities in the agricultural chemical industry will likely decline further as the number of major chemical companies continues to shrink and herbicide sales shift to generic distributors that focus on sales with little emphasis on research. Instead, it is more likely that weed scientists in 2050 will work for small technology companies engaged in engineering, information technology/big data, or biotechnology that does not require large infrastructure. There is abundant opportunity for growth of agricultural implement engineering and manufacturing companies that integrate the use of robotic and weed/crop-sensing technologies with weed control actuators. These companies will need scientists who understand weed biology, ecology, and weed management, but at the same time are familiar with weed-sensing technology and advances in weed/ crop detection and differentiation. Weed science students will also benefit from learning basic plant biology and plant pathology, with the interrelated fields of molecular biology, genomics, bioinformatics, and biotechnology providing fertile ground for developing new insights into plant competition, plant pathogen interactions, or gene silencing. Integration of the diverse and growing knowledge of weed biology and ecology, and factors that affect them, will be necessary for development of integrated weed and resistance management strategies that preserve new technologies as they become available. Above all, students will need to be technologically savvy. This is essential for manipulating and interpreting the big data that are the increasingly the common output from experiments. Students will also need to be ready to engage with growers who are embracing technology in their operations. The amount of data available to growers will only increase, and there will be many opportunities for the weed expert to use such data to understand and manage weed populations.

Research and training needs for weed science.

Meeting the world's requirements for food and fiber crops in 2050 given current weed control methods is a daunting task. Prospects look bleak without new herbicide MOAs or a coordinated strategy to manage and prevent herbicide-resistant weeds. But trends in computing power, robotics, and life sciences suggest that multiple paths exist for improving weed control that can be integrated with existing methods to create more sustainable weed management systems ( Figure 1 ). However, time is short and new technologies may take years to develop and implement, so a sense of urgency is needed. In this article, we have identified priority areas for research and education and hope that progress will follow. We would like to see more investment in research into novel and sustainable methodologies, ideally from a diverse range of sources, including industry and commodities as well as state and federal funders. Universities and government laboratories should create new positions devoted to novel approaches to weed management. Regulatory modifications and incentives that smooth the way for innovation in weed control would also be valuable in accelerating implementation of research advances over the next decade. Finally, today's students are the ones who will deal with this challenge over the course of their professional careers, and they must be trained broadly and encouraged to think creatively to be ready to discover and implement transformational weed management strategies.

Acknowledgments.

The authors acknowledge support for the symposium from WSSA. Additional support to J.H.W. was provided by National Institute of Food and Agriculture project no. 135997. No conflicts of interest have been declared.

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Advances in Weed Science

A Journal of The Brazilian Weed Science Society

Climate change, an emerging threat to weed management

8th international weed science congress – weed science in climate of change, weed management in rice, experimental methods and emerging technologies in weed science, new insights in herbicide physiology, environmental fate of herbicides, about the journal.

Advances in Weed Science , formerly Planta Daninha, is an international peer-reviewed, scientific, and Open Access Journal, published continuously by the Brazilian Weed Science Society ( Sociedade Brasileira da Ciência das Plantas Daninhas  – SBCPD).

Open Access – the journal is open access to the reader. To keep the journal free for readers, article processing charges (APC) must be paid by authors or their institutions. More information in the APC menu.

Recent Articles See All

Herbicide effectiveness and crop yield responses in direct-seeded rice: insights into sustainable weed management.

Adv. Weed Sci. 2024; 42: e020240004

DOI: 10.51694/AdvWeedSci/2024;42:00012

Abstract Background: Conventional method of rice cultivation has proven to be resource intensive, limiting its long term sustainability. On the contrary direct seeding offers a potential rice establishment method provided its increased susceptibility to weed infestation is taken care of. Objective: The principle aim of this study was to evaluate both pre- and post-emergence herbicides for effective weed suppression, while optimizing time window for herbicide application. Methods: A comprehensive two year study was conducted to assess the efficacy of new […]

Keywords: direct seeding ; herbicides ; Rice cultivation ; root growth ; Weed flora ; yield

Interference and level of economic damage of soybean voluntary plants infesting bean

Adv weed sci 2024; 42: e020240072.

DOI: 10.51694/AdvWeedSci/2024;42:00011

Abstract Background: The interference caused by volunteer soybean plants from grains lost before or during harvest can cause economic losses to bean producers due to the competition they cause, especially for succeeding crops. Objective: Therefore, the objective of this work was to determine the competitive ability and economic damage level (EDL) of bean cultivars in the presence of different densities of soybean volunteer plants. Methods: The experiments were installed in completely randomized design, and replicated for two consecutive years, 2020/21 […]

Keywords: Glycine max ; harvest losses ; Phaseolus vulgaris

Mechanistic understanding and sustainable management of non-target site herbicide resistance in modern day agriculture

Adv. weed sci. 2024; 42: e020240056.

DOI: 10.51694/AdvWeedSci/2024;42:00009

Abstract Background The evolution of non-target site resistance (NTSR) to herbicides in weeds has made weed management extremely difficult. Weeds can develop NTSR to herbicides because of changes in one or more physiological processes. Objective This review aims to address the complexities of NTSR by investigating the factors influencing the evolution of NTSR in weeds. It explains mechanisms associated with NTSR and examines sustainable management strategies. Methods This review draws upon an extensive examination of existing literature on NTSR. It […]

Keywords: chemical control ; herbicide resistance ; integrated weed management ; Metabolic resistance

Persistence of S-metolachlor in the soil as affected by moisture content

Adv. weed sci. 2024; 42: e020240042.

DOI: 10.51694/AdvWeedSci/2024;42:00007

Abstract Background: Several factors may affect herbicide fate in the soil, including soil moisture which can affect herbicide availability and degradation and mixture with other degradable herbicides. Objective: The objectives of this research were to evaluate the effects of soil moisture content and association with glyphosate on S-metolachlor persistence in lowland soil. Methods: Greenhouse experiments were conducted in 2011 and repeated in 2012 using a randomized complete block design in a factorial arrangement (3×3×5) with four replications. Factor A included […]

Keywords: carryover ; chloroacetamide ; crop rotation ; Rice Paddy

Impact of different sowing dates and weed management strategies on phenological development, productivity, and thermal efficiencies of direct seeded rice

Adv. weed sci. 2024; 42: e020240069.

DOI: 10.51694/AdvWeedSci/2024;42:00008

Abstract Background Sowing dates and weed management practices could alter several phenological phases of direct seeded rice. However, limited is known about the impacts of these aspects on phenology, thermal efficiencies, and agro-meteorological indices of direct seeded rice. Objective The objective of the study was to evaluate the effect of sowing dates and weed management strategies on phenology, thermal efficiencies, and agro-meteorological indices of direct seeded rice. Methods Two sowing dates [10th May (early) and 3rd June (late)] and six […]

Keywords: Agrometeorological Indices ; Drum Direct Seeded Rice ; Heat Units ; phenology

Glyphosate residues in coffee bean: Impact of application methods and compliance with MRLs

Adv weed sci 2024; 42: e020240060.

DOI: 10.51694/AdvWeedSci/2024;42:00006

Abstract: Background: Farmers often use glyphosate for cost-effective land clearance to streamline coffee harvest processes despite recommendations against its application near the harvest period. However, as set by national and international regulatory authorities, this practice poses a high risk of exceeding the maximum residue limit (MRL) for glyphosate in coffee beans. Objective: In this study, glyphosate residues in green coffee beans were assessed, considering different herbicide application methods (mechanical or manual), nozzles (hooded or unhooded), application volumes, and ripening stages. […]

Keywords: Coffee Harvest ; Global Coffee Platform ; Hooded Nozzle ; Maximum Residue Limit ; Regulatory Authorities ; Safe Re-entry Interval

Lasiodiplodia theobromae and Bipolaris bicolor isolated from infected Eleusine indica ' class="title-article"> Understanding the environmental and herbicide response of Lasiodiplodia theobromae and Bipolaris bicolor isolated from infected Eleusine indica

Adv. weed sci. 2024; 42: e020240063, understanding the environmental and herbicide response of lasiodiplodia theobromae and bipolaris bicolor isolated from infected eleusine indica.

DOI: 10.51694/AdvWeedSci/2024;42:00005

Abstract: Background: In a prior study, Lasiodiplodia theobromae (Pat.) Griffiths and Maubl. and Bipolaris bicolor (Mitra) Shoemaker., were found to suppress the growth of Eleusine indica (L.) Gaertn, but limited information exists on their response to environmental factors and herbicides for integrated E. indica control. Objective: This study aimed to determine the tolerance levels of L. theobromae and B. bicolor to pH, temperature, photoperiod, relative humidity, and herbicides. Methods: The mycelia and conidia of L. theobromae and B. bicolor were […]

Keywords: Bipolaris bicolor ; environmental factors ; herbicides ; Lasiodiplodia theobromae

Machine learning algorithms applied to weed management in integrated crop-livestock systems: a systematic literature review

Adv. weed sci. 2024; 42: e020240047.

DOI: 10.51694/AdvWeedSci/2024;42:00004

Abstract: In recent times, there has been an environmental pressure to reduce the amount of pesticides applied to crops and, consequently, the crop production costs. Therefore, investments have been made in technologies that could potentially reduce the usage of herbicides on weeds. Among such technologies, Machine Learning approaches are rising in number of applications and potential impact. Therefore, this article aims to identify the main machine learning algorithms used in integrated crop-livestock systems for weed management. Based on a systematic […]

Keywords: artificial intelligence ; image processing ; weed control ; Weed prevention

Special Topics See All

• Edinalvo Rabaioli Camargo

Most Cited Articles See All

Conyza bonariensis biotypes resistant to the glyphosate in southern brazil, planta daninha 2007; 25(3): 573-578.

DOI: 10.1590/S0100-83582007000300017

Glyphosate is a non-selective herbicide used for over 20 years to control weeds in Rio Grande do Sul. Horseweed (Conyza bonariensis) is a common weed in Rio Grande do Sul and traditionally sensitive to glyphosate. However, during the last years, some horseweed plants have not shown significant injury symptoms after treatment with glyphosate, suggesting that they are resistant to this herbicide. Aiming to evaluate the response of a population of horseweed plants to glyphosate, one field and two greenhouse experiments […]

Keywords: EPSP inhibitors ; herbicide resistance

Interference periods of weeds in the sugarcane culture. I – Purple nutsedge

Planta daninha 2000; 18(2): 241-251.

DOI: 10.1590/S0100-83582000000200006

The objective of this research was to study interference periods between weeds and sugarcane culture in a experimental area located in Pradópolis, São Paulo State, Brazil. In these experiment, sugarcane was planted in May of 1995, and harvested 15 months later. The climatic conditions in São Paulo State during the months that follow sugarcane planting in the experiment (normal time when growers plant sugarcane), are characterized by negative balance of rain and evapotranspiration and mild temperatures, and the rainy season […]

Keywords: competition ; Cyperus rotundus ; Saccharum officinalis ; weed

Corn yield response to weed and fall armyworm controls

Planta daninha 2010; 28(1): 103-111.

DOI: 10.1590/S0100-83582010000100013

The interference imposed the by weeds on corn decreases practically all vegetative characteristics. As consequence, the green ear and grain yield are also reduced. Losses due to the fall armyworm (Spodoptera frugiperda) attack can reduce corn grain yield up to 34%. In general, weed and insect control issues are addressed separately in research papers. Nevertheless, interaction between weeds and insects may exist. This study aimed to evaluate green ear and corn grain yield response to weed and fall armyworm control. […]

Keywords: Azadirachta indica ; Spodoptera frugiperda ; weed-pest interaction ; Zea mays

Responses of Plants to Pesticide Toxicity: an Overview

Planta daninha 2019; 37: e019184291.

DOI: 10.1590/S0100-83582019370100065

ABSTRACT: Pesticides are applied all over the world to protect plants from pests. However, their application also causes toxicity to plants, which negatively affects the growth and development of plants. Pesticide toxicity results in reduction of chlorophyll and protein contents, accompanied by decreased photosynthetic efficiency of plants. Pesticide stress also generates reactive oxygen species which causes oxidative stress to plants. To attenuate the negative effects of oxidative stress, the antioxidative defense system of plants gets activated, and it includes enzymatic […]

Keywords: antioxidative defense system ; oxidative stress ; physiological responses

Resistance of italian ryegrass (Lolium multiflorum) to glyphosate

Planta daninha 2004; 22(2): 301-306.

DOI: 10.1590/S0100-83582004000200018

Italian ryegrass (Lolium multiflorum) is cultivated as forage and/or cover crop in no-till system. However, it is also a serious weed in wheat and other winter cereals in Southern Brazil. Experiments were conducted at greenhouse and field conditions to evaluate the susceptibility of two ryegrass biotype to glyphosate as well as the efficacy of other herbicides on the post-emergence control of the species for sowing wheat under no-till system. The experimental design was a completely randomized design for the greenhouse […]

Keywords: EPSPs injury ; herbicide ; post-emergence ; resistance

Potential of sorghum and pearl millet cover crops in weed supression in the field: II – Mulching effect

Planta daninha 2004; 22(1): 1-10.

DOI: 10.1590/S0100-83582004000100001

The weed supression capacity of cover crops is well known and explored, although only a few works have been conducted on the relative importance of the physical and allelopathic effects on this phenomenon. Two trials were carried out in the field, in 1999/2000 and 2000/2001, at the experimental area of the University of Rio Grande do Sul, Brazil, arranged in a randomized experimental block design with four replications to evaluate the effects of sorghum and pearl millet mulch on weedsupression. […]

Keywords: allelopathy ; Pennisetum americanum ; physical factors ; Sorghum spp ; straw levels

Seed longevity of red rice ecotypes buried in soil

Planta daninha 2006; 24(4): 611-620.

DOI: 10.1590/S0100-83582006000400001

Red rice is a troublesome weed in irrigated rice production and is spread through contaminated commercial rice seed and machinery. Seed dormancy is a major trait for red rice. Studies were carried out at two locations to determine red rice seed longevity in the soil of several ecotypes from four US states. Five months after burial near Beaumont, Texas only three ecotypes had viable seed (<1%) when buried at 5 cm, but 9 ecotypes had viable seed after two years […]

Keywords: blackhull ecotypes ; Oryza sativa ; red rice ; rice ; seed dormancy ; seed survival ; strawhull ecotypes

Brachiaria brizantha intercrop' class="title-article"> Influence of herbicides and sowing systems on maize – Brachiaria brizantha intercrop

Planta daninha 2005; 23(1): 59-67, influence of herbicides and sowing systems on maize – brachiaria brizantha intercrop.

DOI: 10.1590/S0100-83582005000100008

The aim of this study was to evaluate the occurrence of weeds, nutritional state and yield of maize – B. brizantha

Keywords: atrazine ; crop-livestock integration ; nicosulfuron

Ecological factors associated to aquatic macrophyte colonization and growth and management challenges

Planta daninha 2002; 20(spe): 21-33.

DOI: 10.1590/S0100-83582002000400003

The aquatic macrophytes have been considered an important community in freshwater ecosystems. However, their excessive colonization and growth usually cause serious impacts on multiple use of these ecosystems. Most aquatic environments are colonized at different degrees by aquatic plants in some phase of ecological succession. Nevertheless, massive growth is usually associated with anthropogenic actions such as introduction of alien species and habitats of alterations. Knowledge about ecology and biology of the species that colonize tropical ecosystems is still scarce. This […]

Keywords: aquatic ecosystems ; ecological succession ; limiting factors ; reservoirs

Use of growth retardants in wheat

Planta daninha 2009; 27(2): 379-387.

DOI: 10.1590/S0100-83582009000200022

In general, lodging has been controlled by restricting nitrogen fertilizer application and/or using short cultivars. Growth retardants can also be used to solve this problem.The objective of this study was to evaluate the effect of rates and application times of three growth retardants on Pioneiro wheat cultivar. The trial was carried out in Viçosa-MG, from May to September 2005, in a factorial and hierarchical scheme, in a randomized block design with four replications and a control treatment. The treatments consisted […]

Keywords: chlormequat ; paclobutrazol ; plant height ; trinexapac-ethyl ; Triticum aestivum ; yield

Avena sterilis subsp. ludoviciana ) populations: Field margins vs. within fields' class="title-article"> Herbicide resistance development in winter wild oat ( Avena sterilis subsp. ludoviciana ) populations: Field margins vs. within fields

Adv. weed sci. 2024; 42: e020240061, herbicide resistance development in winter wild oat ( avena sterilis subsp. ludoviciana ) populations: field margins vs. within fields.

DOI: 10.51694/AdvWeedSci/2024;42:00002

Abstract: Background: The resistance of grass weeds to herbicides is expanding in wheat fields. An effective strategy for managing herbicide resistance is to prevent the likelihood of resistance development spreading from field margins to within fields. Objective: This study was conducted to evaluate the resistance development in winter wild oat (Avena sterilis subsp. ludoviciana) populations collected from within fields and field margins of 11 winter wheat fields to the commonly used ACCase and ALS-inhibiting herbicides. Methods: Seeds of 22 A. […]

Keywords: ACCase inhibitor ; ALS inhibitor ; herbicide resistance ; winter wild oat

Characterization of junglerice: growth habit and morphological plasticity determined by population density

Adv. weed sci. 2024; 42: e020240059.

DOI: 10.51694/AdvWeedSci/2024;42:00003

Abstract: Background: Numerous studies have described junglerice (Echinochloa colona) competitiveness against crops, but its behavior concerning plant density as an outcome of intraspecific competition has not been well documented. Objective: This study aimed to characterize morphology based on population density and determine the degree of density dependence. Methods: Junglerice was grown in field conditions in a range of densities from 0.25 to 300 plants m-2. Plant height and width, tillering, aerial dry weight, seed weight, seed number, and hundred-seed weight […]

Keywords: adaptability ; Aerial structures ; Density Dependence ; Intraspecific Interactions ; Monospecific Experiments

Echinochloa colona exposed to sublethal doses of four commonly-used rice herbicides and high-temperature stress' class="title-article"> Seed production potential of Echinochloa colona exposed to sublethal doses of four commonly-used rice herbicides and high-temperature stress

Adv. weed sci. 2024; 42: e020240052, seed production potential of echinochloa colona exposed to sublethal doses of four commonly-used rice herbicides and high-temperature stress.

DOI: 10.51694/AdvWeedSci/2024;42:00001

Abstract: Background: Echinochloa colona (junglerice), a troublesome weed in rice, is resistant to 15 herbicide active ingredients. High temperatures are linked to reduction of herbicide efficacy. Objective: Evaluate growth and seed production of junglerice, after five generations of recurrent selection with sublethal dose of rice herbicides under heat stress. Methods: Junglerice plants previously subjected to recurrent selection with herbicides and heat stress for three cycles were exposed to further iterative cycles of selection with heat stress (45 °C) and sublethal […]

Keywords: abiotic stress ; Fecundity ; Fitness penalty ; Heat stress ; Increased fitness ; Recurrent selection ; weed resistance ; Weediness

Experimental methods for phenotypic and molecular analyses of seed shattering in cultivated and weedy rice

Adv. weed sci. 2023; 41: e020230049.

DOI: 10.51694/AdvWeedSci/2023;41:00030

Abstract The seed shattering trait has been repeatedly reshaped during rice evolution. Reduced in cultivated rice and increased in weedy rice, shattering is of great agronomic importance because of its association with yield losses. Since its first descriptions, the phenotypic patterns and the genetic regulation of cultivated and weedy rice seed shattering have been extensively studied, with a variety of methods and techniques. The aim of this review is to discuss and recommend the most suitable experimental methods for phenotypic […]

Keywords: Abscission layer ; Breaking tensile strength ; Oryza sativa ; Seed shattering ; Weedy rice evolution

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Advances in Weed Science Journal Launch

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June 25, 2024

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Farmland weeds can help combat pests

by University of Bonn

Leaving some weeds between crops can help to combat pests on agricultural land, according to a new study carried out by the University of Bonn. This step has particularly positive effects in combination with other measures: the cultivation of different types of crops and planting strips of wildflowers. The results have now been published in the Journal of Pest Science .

Intercropping, i.e. planting different types of crops on the same field has a number of benefits: The crops have different requirements and the crops face less competition than when grown in monocultures. This means that they make better use of the water and nutrients and deliver a better yield overall. Some types of crops—such as beans—are also able to fix nitrogen from the air, thereby delivering this nutrient as a natural fertilizer. The other crop also benefits as a result.

"Intercropping also makes it difficult for weeds to grow," says Prof. Thomas Döring from the Institute of Crop Science and Resource Conservation (INRES) at the University of Bonn. "The crops are also much less infested with pests. Insects usually specialize on one type of plant and they thus find fewer of the right type of plants with intercropping."

While these benefits have been proven many times, Döring and his colleague Dr. Séverin Hatt have now investigated whether these benefits can be improved even further in combination with other measures.

Strips of wildflowers attract aphid predators

The researchers cultivated two different crop mixes—beans and wheat and poppy and barley—in a field experiment lasting two years. In addition, they planted strips of wildflowers along the edges of the fields. "These strips attract beneficial insects that feed on pests," explains Döring, who is also a member of the PhenoRob Cluster of Excellence and the transdisciplinary research area "Sustainable Futures." "These insects include hoverflies and ladybirds, whose larvae are very effective predators of aphids."

In fact, the researchers found that aphid colonization of the mixed crops fell significantly next to the wildflower strips. They also discovered another effect: Mixing beans and wheat or poppy and barley naturally suppressed the growth of weeds without actually eradicating them completely. If the farmer took no additional measures, wild plants would continue to randomly grow across the field.

Residual weeds make it easier for beneficial insects to spread

"We have now been able to demonstrate that these residual weeds make it easier for beneficial insects to spread deeper into the field," says Döring. "And they did not reduce the yield in the process. In contrast, the study showed that they even helped to control pests."

The results were collected from fields that were cultivated under organic farming conditions. The extent to which these findings can be transferred to conventional farming still needs to be investigated.

However, the researchers are already able to issue a clear recommendation for organic farming based on their findings: Farmers should plant wildflower strips, use a greater mix of seeds and consider tolerating some residual weeds. This combination of measures will help them keep pests under control and at the same time maintain weeds at an acceptable level.

Provided by University of Bonn

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Legal weed limps into next phase in Germany

So-called cannabis clubs will be allowed to sell the drug legally in Germany starting Monday, but in practice it will be some time before the associations get up and running.

Germany legalized cannabis in April, allowing adults to possess 25 grams (0.9 ounces) and cultivate up to three marijuana plants at home.

As the next step in the reform, from July 1 it will be possible to legally obtain weed through regulated "cannabis clubs" in the country.

The associations will be allowed to have up to 500 members each and will be able to distribute up to 50 grams of cannabis per person per month.

Mariana Cannabis, an umbrella organization for around 180 future cannabis clubs across Germany, already has around 20,000 members.

But at the group's production site in Leverkusen, just north of the western city of Cologne, there are no seeds or cuttings to be seen.

That is because before the clubs can begin operating, they must apply for a license that can take up to three months to obtain.

"We are impatient, but we still have to wait," Keno Mennenga, a spokesman for Mariana Cannabis, told AFP.

Black market

In Munich, members of the Cantura cannabis club have been paying 25 euros ($27) a month since March, before the first part of the law even came into force.

The club has invested thousands of euros in office space, security and cultivation equipment, according to its CEO, Fabian Baumann.

"We need around eight weeks from cutting to harvesting," he said. "If everything goes well, we'll be able to supply cannabis to our members this year. That would be wonderful."

When launching the first phase of the law in April, the German government insisted that it was not promoting cannabis use but rather seeking to curb the black market for the drug .

"The German model is based on a gradual approach. The idea is to be cautious and to evaluate in real time," said Ivana Obradovic, an expert with the France-based Monitoring Centre for Drugs and Drug Addiction (OFDT).

She said the model had incorporated lessons from several other systems that have been tested around the world.

"The idea is to keep control of supply so that it doesn't prosper rapidly," Obradovic said.

In the United States, the legalization of cannabis in many states has created "a situation of overproduction, particularly in California and Oregon, where production exceeds local demand by five to six times", she said.

Nonetheless, all countries that have legalized cannabis have seen some level of decline in black market sales.

In Canada, around 75 percent of cannabis users now buy through legal channels, compared with just 40 percent in 2018, the year the drug was legalized, according to the OFDT.

Mennenga, at Mariana Cannabis, acknowledged that in Germany, "The black market is in control and it's getting worse".

"We can stop it getting worse."

Political fears

Bluetezeit, a Berlin-based start-up specializing in cannabis products, hopes that Germany will eventually authorize the sale of the drug in pharmacies or licensed shops.

For Nikolaos Katsaras, head of the company, only a competitive and lucrative legal market can compete with a black market that has been established for years.

In the meantime, Bluetezeit has already built up an online community of 10,000 members.

The company plans to develop cannabis clubs while also selling cannabis products online and offering consultations for people who want to use the drug for medical purposes.

Katsaras said he aimed to "take the pulse of the market" in deciding the right direction for the company.

His only fear is that a general election set for Germany in 2025 brings a change of government, which could put the brakes on the industry's development.

Friedrich Merz, leader of the Christian Democrats (CDU), the main opposition party, has said he will annul the legalization of cannabis if his party returns to power.

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