Herbicide-resistant Palmer amaranth is creating additional challenges for producers choosing to adopt a furrow-irrigated rice production system due to the absence of a sustained flood, enabling extended weed emergence. Fluridone has been shown to control Palmer amaranth effectively in cotton production systems and was recently registered for use in rice. Experiments were initiated in 2022 and 2023 to evaluate 1) Palmer amaranth control and rice tolerance to preemergence- and postemergence-applied fluridone at a 0.5x (84 g ai ha-1) and 1x rate (168 g ai ha-1) on a silt loam soil and 2) the effect of various herbicide programs containing fluridone on Palmer amaranth biomass, seed production, and rough rice grain yield. Preemergence applications of fluridone at a 1x rate in combination with clomazone resulted in 84% control of Palmer amaranth 21 d after treatment (DAT). Fluridone, in combination with clomazone preemergence, caused up to 36% rice injury 21 DAT; however, early season injury did not negatively affect rice yields. Palmer amaranth biomass and fecundity were reduced with herbicide programs that included fluridone plus florpyrauxifen-benzyl, and, in some instances, there was no Palmer amaranth biomass or seed production following multiple applications of both herbicides. Fluridone- and florpyrauxifen-benzyl-based herbicide programs achieved effective control of Palmer amaranth when applied timely, but injury to hybrid rice is enhanced with preemergence applications of fluridone that are not permitted with the current label.

Cover crop adoption is increasing among growers with the occurrence of herbicide-resistant weed species. A field study conducted at three sites from autumn 2021 through the crop harvest in 2022 in Alabama aimed to evaluate the combined effect of cover crop residue and herbicides for weed control and improved cotton lint yield. The experiment was conducted in split-plot design with main plots consisting of six cover crop treatments: cereal rye, crimson clover, oat, radish, cover crop mixture, and winter fallow. The subplots included four herbicide treatments: (i) preemergence, pendimethalin + fomesafen, (ii) postemergence, dicamba + glyphosate + S-metolachlor, (iii) preemergence followed by postemergence, and (iv) nontreated (NT) check. Cover crops, excluding radish, exhibited greater weed biomass reduction than winter fallow with corresponding herbicide treatments of either preemergence, postemergence, or preemergence + postemergence as compared to control (winter fallow and NT check). Considering preemergence + postemergence treatment, cereal rye, crimson clover, oat, and cover crop mixture provided >95% weed biomass reduction as compared to control. Looking at the overall effect of cover crop, cereal rye outperformed and showed greater weed biomass reduction than radish relative to control. Preemergence + postemergence herbicide treatment resulted in greater lint yield than other treatments. Cotton in cereal rye plots had a greater lint yield than in winter fallow at one out of three locations. In conclusion, integrating herbicides and incorporating high-residue cover crops such as cereal rye is an effective weed management strategy to control troublesome weeds.

Georgia growers can benefit from double-cropping grain sorghum following watermelon to maximize land use and add economic value to their operations. However, capitalizing on the economic advantages of harvesting two crops within a single season must account for potential herbicide injury to rotational crops. An integrated weed management strategy that includes a preplant application of fomesafen and terbacil is recommended for weed control in watermelon production systems. However, currently labeled plant-back restrictions for grain sorghum require a minimum of 10 and 24 mo for fomesafen and terbacil, respectively. Therefore this research aimed to determine the tolerance of grain sorghum to fomesafen and terbacil following soil applications applied 90 to 100 d before planting (DBP). Experiments were conducted at the University of Georgia Ponder Research Farm from 2019 to 2023. The experimental design was a randomized complete block with four replicates. Five rates of fomesafen (35, 70, 140, 210, and 280 g ai ha−1), four rates of terbacil (3.5, 7.0, 10.5, and 14.0 g ai ha−1), and a nontreated control were evaluated. In 2019, fomesafen caused significant sorghum leaf necrosis, plant density reductions, height reductions, and yield reductions of at least 16%, especially when applied at rates ≥ 210 g ai ha−1. Terbacil had little to no effect on sorghum injury, density, height, or yield in any year. These results suggest that sorghum has sufficient tolerance to terbacil when applied 90 to 100 DBP. In four of five years, sorghum had an acceptable tolerance to fomesafen when applied 90 to 100 DBP. However, yield losses observed in 2019 suggest that caution should be taken when fomesafen is applied 90 to 100 DBP grain sorghum at ≥ 210 g ai ha−1.

Pink purslane is often ranked as one of the most troublesome weeds in vegetable production systems in Georgia. Pink purslane encroachment along field edges and in-field of agronomic crops has recently increased. Postemergence herbicides are an effective component of agronomic crop weed management. However, little research has addressed pink purslane control in agronomic crops. Therefore, greenhouse and field studies were conducted from 2022 to 2023 in Tifton, Georgia, to evaluate the response of pink purslane to postemergence herbicides commonly used in agronomic crops. Greenhouse screening provided preliminary evidence whereby 13 of the 21 postemergence herbicides evaluated provided ≥80% aboveground biomass reductions. These 13 herbicides were then used for field studies. Results from the field studies, pooled across two locations, indicated that only three of the 13 herbicides provided aboveground biomass reductions of ≥70% compared to the nontreated control. Those herbicides included atrazine at 1,682 g ai ha−1, glufosinate at 656 g ai ha−1, and lactofen at 219 g ai ha−1 with 79%, 70%, and 83% biomass reduction, respectively (P < 0.05). This research suggests that many of the postemergence herbicides used on agronomic crops will not effectively control pink purslane. Thus, when trying to manage pink purslane with postemergence herbicides in agronomic crops, growers should plant crops or cultivars that are tolerant of either atrazine, glufosinate, lactofen, or a combination of these.

The adsorption and degradation of the herbicide triasulfuron [2-(2-chloroethoxy)-N-[[(4-methoxy-6-methyl-1,3,5-triazin-2-yl)amino]carbonyl]benzenesulfonamide] (CMMT) on homoionic Fe3+-, Al3+-, Ca2+-, or Na+-exchanged montmorillonite in aqueous medium were studied. Ca- and Na-exchanged montmorillonite were ineffective in the adsorption and degradation of triasulfuron. The adsorption on Fe-and Al-exchanged montmorillonite was rapid, and equilibrium was attained after 5 min. Degradation of the herbicide was slow and the type of the degradation products depended on the nature of the exchangeable cations. In the presence of Fe3+-rich montmorillonite, the metabolites 2-(2-chloro-ethoxy)benzenesulfonamide (CBSA), 2-(2-chloroethoxy)-N-[[(4-hydroxy-6-methyl-1,3,5-triazin-2-yl)amino]carbonyl]benzenesulfonamide (CHMT), and l-[2-(2-chloroethoxy)benzene-l-sulfonyl]-7-acetyl-triuret (CBAT) were the only identified products, whereas 2-amino-4-methoxy-6-methyltriazine (AMMT), CBSA, CHMT, and CBAT were the primary metabolites for the Al3+-rich montmorillonite. A Fourier transform infrared (FT-IR) study of montmorillonite samples after the interaction with triasulfuron in organic solution suggests that the hydrolysis mechanism involves the adsorption of the herbicide on the 2:1 layers.

The adsorption of the herbicides quinmerac 7-chloro-3-methylquinoline-8-carboxylic acid (QMe) and quinclorac 3,7-dichloroquinoline-8-carboxylic acid (QCl) on homoionic Fe3+-, Al3+-, Cu2+-, Ca2+-, K+- and Na+-exchanged montmorillonite was studied in aqueous solution. Adsorption data were fitted to the logarithmic form of the Freundlich equation. Ca- and Na-exchanged montmorillonites were ineffective in the adsorption of QMe. On the other hand, the QMe adsorption on Fe-exchanged montmorillonite was rapid and the equilibrium was attained after 15 min. An H-type isotherm was observed for the QMe adsorption on Fe-clay, indicating a high affinity of the solute for the sorption sites and almost complete adsorption from dilute solution. On the other hand, the adsorption isotherm of QMe on Al- and K-clay was of the S-type. This shape suggests that the solvent molecules may compete for the sorption sites. A Fourier transform infrared (FTIR) study suggested that the adsorption mechanism of QMe on Fe-, Al- and K-clay involves the protonation of QMe molecule due to the acidic water surrounding the saturating cations. The greater acidity of Fe-clay compared with Al- and K-clay explains both the lower QMe adsorption observed on Al and K systems and the lack of adsorption on Na and Ca systems. In contrast, the formation of a Cu complex permitted QMe to be adsorbed to a large extent to Cu-clay as shown by FTIR analysis. The QCl was adsorbed only by Fe-clay and the adsorption isotherm of QCl on Fe clay was of the S-type. This finding is consistent with the lower basic character of the QCl molecule nitrogen. In fact, the replacement of the electron-releasing methyl group in QMe with an electron-withdrawing Cl atom to form QCl makes the nitrogen lone-pair electrons of the quinoline ring unavailable for either protonation or complexation.

Herbicides are the primary tool for controlling weeds in peanut (Arachis hypogaea L.) and are crucial to sustainable peanut production in the United States. The literature on chemical weed management in peanut in the past 53 yr (1970 to 2022) in the United States was systematically reviewed to highlight the strengths and weaknesses of different herbicides and identify current research gaps in chemical weed management. Residual weed control in peanut is achieved mainly with dimethenamid-P, ethalfluralin, pendimethalin, and S-metolachlor. More recently, the use of the protoporphyrinogen oxidase inhibitor flumioxazin and acetolactate synthase inhibitors, such as diclosulam, for residual weed control in peanut has increased considerably. Postemergence broadleaf weed control in peanut is achieved mainly with acifluorfen, bentazon, diclosulam, imazapic, lactofen, paraquat, and 2,4-DB, while the graminicides clethodim and sethoxydim are the major postemergence grass weed control herbicides in peanut. Although several herbicides are available for weed control in peanut, no single herbicide can provide season-long weed control due to limited application timing, lack of extended residual activity, variability in weed control spectrum, and rotational restrictions. Therefore, effective weed management in peanut often requires herbicide mixtures and/or sequential application of preplant-incorporated, preemergence, and/or postemergence herbicides. However, the available literature showed a substantive range in herbicide efficacy due to variations in environmental conditions and flushes of weed germination across years and locations. Despite the relatively high efficacy of herbicides, the selection of herbicide-resistant weeds is another area of increasing concern. Future research should focus on developing new strategies for preventing or delaying the development of resistance and improving herbicide efficacy within the context of climate change and emerging constraints such as water shortages, rising temperatures, and increasing CO2 concentration.

Weed management is a significant challenge that must be addressed both globally and in Australia, where traditional methods of control have become limited. The avoidance of mechanical practices has resulted in reduced erosion but has also led to an increased reliance on chemicals and a subsequent increase in rates of herbicide resistance. To address this challenge, alternative forms of weed management, such as electric weed control (electro-weeding), need to be considered. Electric weed control functions by transferring electrical current through the target plant following electrode contact, causing the plant’s cells to burst and either killing the plant or suppressing its growth. However, a multitude of variables, such as electrical power and speed of application, weed morphology, and site-specific environmental conditions, can impact the use of electric weed control and its efficacy. While electric weed control holds promise, and despite its recent global popularity with numerous companies producing machinery, the applicability, efficacy, and risks of using electric weed control internationally and in Australia have yet to be thoroughly analyzed. Given the existing knowledge gaps, this review provides a comprehensive overview of the theory and recent advances in electric weed control. Additionally, the review discusses the potential for resistance development and safety risks associated with electric weed control and presents an overview of modern machines and their application in various settings. It also highlights the need for further research to determine the applicability and efficacy of implementing this new weed control method before widespread adoption and integration into pest management strategies.

Potato is the third most important staple food crop globally following rice and wheat. In the United States, potato is grown on approximately 410,000 ha with a farm-gate value of US$1,032 million. In Canada, potato is grown on approximately 134,000 ha with a farm-gate value of US$235 million. The objective of this manuscript, compiled by the Weed Science Society of America Weed Loss Committee, was to estimate potato yield loss caused by weed interference. Potato yield data from weedy and weed-free plots (or plots with >95% weed control) was obtained from researchers working on weed management in potato in the United States and Canada or from published manuscripts from 2000 to 2018. Potato yield loss from weed interference was 12% to 61% when no weed management tactics were implemented. The average yield loss for all states/provinces (where data was obtained) due to weed interference was 44%. Weed interference would cause a farm-gate loss of approximately US$465 million and US$61 in the United States and Canada, respectively, if weeds are not controlled. These results indicate that weed management is critical for successful potato production, and that an ongoing need for research exists on weed management in this crop.

The topic of sustainability is popular in mainstream media and a common discussion theme, particularly for the agriculture discipline that serves the entire world. Individuals and corporations often have a desire to be sustainable in their practices, but the commentary on “being sustainable” can be confusing in terms of realistic practices. To define whether weed science is sustainable one must first identify the resource or object to be sustained. From a historical perspective, weed control in the United States over the past 40 yr has revolved around no-tillage row crop acres. The implementation of no-till or reduced till has undeniable benefits in sustaining natural resources, especially two of our most valuable resources: soil and water. While the overall trend toward chemical weed control has been shown to decrease agriculture’s impact on the environment, depending solely on herbicides is not sustainable long term with the rise in herbicide-resistant weed species. We also consider the benefits and challenges associated with agronomic trends within the context of sustainability and expand consideration to include emerging technology aligned to human health and environmental stewardship. The key to improving farming is producing more and safer food, feed, and fiber on less land while reducing adverse environmental effects, and this must be accomplished with the backdrop of human population growth and the desire for an improved standard of living globally. Emerging technologies provide new starting points for sustainable weed management solutions, and the weed science community can initiate the conversation on sustainable practices and share advancements with our colleagues and community members. In addition to broadening the sustainability concept, targeted and relevant communication tools will support the weed science community to have successful and impactful discussions.

Weeds represent one of the most important biotic threats to agricultural plant health, and the potential global impact of weeds on crop yields is similar to that of all other pests (animal pests and pathogens) combined. Canola is the most-grown crop in Canada based on seeded area and generates on average Can$29.9 billion in economic activity each year. The objective of this report, sponsored by the Weed Science Society of America Weed Loss Committee, was to provide an updated estimate of potential yield and monetary losses due to weed interference in spring canola grown in Canada and the United States. Quantitative yield data from field experiments were provided by researchers and weed science professionals in the northern Great Plains region; the major canola-producing area of North America. Overall, 89 yield loss estimates were compiled, covering the 18-yr period from 2003 to 2020. Average canola yield losses due to weed interference in Alberta, Saskatchewan, Manitoba, and North Dakota were 35%, 30%, 18%, and 28%, respectively. Potential yield losses weighted by canola harvested area averaged 30%, 28%, and 30% for Canada, the United States, and both countries combined, respectively. Therefore, unfettered weed interference in spring canola represents a potential monetary loss of Can$2.21 billion, $0.16 billion, and $2.37 billion for farmers in Canada, the United States, and both countries combined. The realization of such losses could manifest through continued selection for herbicide-resistant weeds, indicating the critical need for canola farmers to diversify resistance selection pressures by implementing proactive integrated weed management programs.

Limited information exists on the global economic impact of glyphosate-resistant (GR) weeds. The objective of this manuscript was to estimate the potential yield and economic loss from uncontrolled GR weeds in the major field crops grown in Ontario, Canada. The impact of GR weed interference on field crop yield was determined using an extensive database of field trials completed on commercial farms in southwestern Ontario between 2010 and 2021. Crop yield loss was estimated by expert opinion (weed scientists and Ontario government crop specialists) when research data were unavailable. This manuscript assumes that crop producers adjust their weed management programs to control GR weeds, which increases weed management costs but reduces crop yield loss from GR weed interference by 95%. GR volunteer corn, horseweed, waterhemp, giant ragweed, and common ragweed would cause an annual monetary loss of (in millions of Can$) $172, $104, $11, $3, and $0.3, respectively, for a total annual loss of $290 million if Ontario farmers did not adjust their weed management programs to control GR biotypes. The increased herbicide cost to control GR volunteer corn, horseweed, waterhemp, giant ragweed, and common ragweed in the major field crops in Ontario is estimated to be (in millions of Can$) $17, $9, $2, $0.1, and $0.02, respectively, for a total increase in herbicide expenditures of $28 million annually. Reduced GR weed interference with the adjusted weed management programs would reduce farm-gate monetary crop loss by 95% from $290 million to $15 million. This study estimates that GR weeds would reduce the farm-gate value of the major field crops produced in Ontario by Can$290 million annually if Ontario farmers did not adjust their weed management programs, but with increased herbicide costs of Can$28 million and reduced crop yield loss of 95% the actual annual monetary loss in Ontario is estimated to be Can$43 million annually.

Downy brome (Bromus tectorum L.) is a highly invasive winter annual grass that can fill open niches in native plant communities. Prescribed burning is often used to control B. tectorum and can be combined with herbicide treatments to extend the duration of control and promote the native plant community. Several herbicides have been evaluated in conjunction with burning for B. tectorum control, although the herbicide indaziflam has not. In September 2017, two B. tectorum–infested sites were burned in Colorado foothill shrublands. In March 2018, indaziflam was applied alone or in combination with glyphosate, rimsulfuron, or imazapic. These treatments were compared with imazapic plus glyphosate as a standard. All treatments were made within burned and non-burned areas in a crossed-nested design. Bromus tectorum cover and the desirable plant community responses were evaluated 1 and 2 yr after treatment (YAT). In non-burned areas, all indaziflam treatments reduced B. tectorum cover compared with the control. In contrast, reductions from the imazapic treatments did not persist after the first year. Most post-burn treatments further decreased B. tectorum cover compared with the non-burned treatments. The most effective treatments (indaziflam 44 and 73 g ai ha−1 + imazapic 123 g ae ha−1) provided similar levels of control (<1% B. tectorum cover at 2 YAT), with or without burning. Desirable plant cover, richness, and diversity were not negatively impacted by burning or herbicide treatments. Plant diversity and species richness increased at Site 2 when burning was followed by indaziflam treatments. This study indicates that B. tectorum control using indaziflam can be enhanced when applied after burning, and the combinations with imazapic or rimsulfuron provide a wider application window compared with the combination with glyphosate.

Yield losses due to weeds are a major threat to wheat production and economic well-being of farmers in the United States and Canada. The objective of this Weed Science Society of America (WSSA) Weed Loss Committee report is to provide estimates of wheat yield and economic losses due to weeds. Weed scientists provided both weedy (best management practices but no weed control practices) and weed-free (best management practices providing >90% weed control) average yield from replicated research trials in both winter and spring wheat from 2007 to 2017. Winter wheat yield loss estimates ranged from 2.9% to 34.4%, with a weighted average (by production) of 25.6% for the United States, 2.9% for Canada, and 23.4% combined. Based on these yield loss estimates and total production, the potential winter wheat loss due to weeds is 10.5, 0.09, and 10.5 billion kg with a potential loss in value of US$2.19, US$0.19, and US$2.19 billion for the United States, Canada, and combined, respectively. Spring wheat yield loss estimates ranged from 7.9% to 47.0%, with a weighted average (by production) of 33.2% for the United States, 8.0% for Canada, and 19.5% combined. Based on this yield loss estimate and total production, the potential spring wheat loss is 4.8, 1.6, and 6.6 billion kg with a potential loss in value of US$1.14, US$0.37, and US$1.39 billion for the United States, Canada, and combined, respectively. Yield loss in this analysis is greater than some previous estimates, likely indicating an increasing threat from weeds. Climate is affecting yield loss in winter wheat in the Pacific Northwest, with percent yield loss being highest in wheat-fallow systems that receive less than 30 cm of annual precipitation. Continued investment in weed science research for wheat is critical for continued yield protection.

Multiple herbicide-resistant populations of horseweed [Conyza canadensis (L.) Cronquist] continue to spread rapidly throughout Ontario, notably in areas where no-till soybean [Glycine max (L.) Merr.] is grown. The occurrence of multiple herbicide resistance within these populations suggests that the future role of herbicide tank mixtures as a means of control will be limited. An integrated weed management strategy utilizing complementary selection pressures is needed to reduce the selection intensity of relying solely on herbicides for control. Field studies were conducted in 2018 and 2019 to test the hypothesis: if fall-seeded cereal rye (Secale cereale L.) can reduce C. canadensis seedling density and suppress seedling growth, then the interaction(s) of complementary selection pressures of tillage, cereal rye, and herbicides would improve the level of C. canadensis control. Laboratory studies were conducted to determine whether the allelopathic compound 2-benzoxazolinone (BOA) affected the root development of C. canadensis seedlings. The interactions observed among multiple selection pressures of tillage, cereal rye, and herbicides were inconsistent between the 2 yr of study. A monoculture of cereal rye seeded in the fall, however, did reduce seedling height and biomass of C. canadensis consistently, but not density. This reduction in seedling height and biomass was likely caused by the allelopathic compound BOA, which reduced seedling root development. Control of C. canadensis seedlings in the spring required the higher registered rates of dicamba or saflufenacil. The addition of shallow fall tillage and the presence of cereal rye did not improve the variability in control observed notably with 2,4-D or the lower rates of saflufenacil or dicamba. With the implementation of complementary weed management strategies, environmental variables in any given year will likely have a direct influence on whether these interactions are additive or synergistic.

Common teasel is a troublesome invasive weed in North and South America. Additional information on the efficacy of herbicide application and mowing at different growth stages will help in common teasel management. First, an outdoor pot experiment was performed to assess the effects of increasing application rates and combinations of glyphosate and 2,4-D amine when applied at the 4-leaf, rosette, and bolting stages. Second, field experiments were performed to evaluate the impact of time of cutting on invasive common teasel height, head number, and head length. Finally, germinability of seeds collected from naturally growing plants was determined to evaluate the feasibility of mowing invasive common teasel after flowering. Only glyphosate applied at 1.08 kg ae ha−1 at the 4-leaf stage provided adequate control (>90%). Although control was not satisfactory (<90%) when applying glyphosate at 2.16 kg ae ha−1 at the rosette and bolting stages, and 2,4-D at 1.75 kg ai ha−1 at 4-leaf stage, significant injury and biomass decline were observed. Glyphosate and 2,4-D combinations did not improve common teasel control compared with single applications of each. Cutting rosettes strongly reduced inflorescence production (34%–49%) and cutting flowering plants prevented total regrowth. Germination of seeds averaged 14% when harvested 10 d after flowering, and maximum seed germination (>90%) occurred 30 d after flowering. Glyphosate applied alone at the recommended commercial rate early in the growing season, together with cutting at the flowering stage, may be the most beneficial way of controlling invasive common teasel.

Potential yield losses in grain sorghum due to weed interference based on quantitative data from the major grain sorghum-growing areas of the United States are reported by the WSSA Weed Loss Committee. Weed scientists and extension specialists who researched weed control in grain sorghum provided data on grain sorghum yield loss due to weed interference in their region. Data were requested from up to 10 individual experiments per calendar year over 10 yr between 2007 and 2016. Based on the summarized information, farmers in Arkansas, Kansas, Missouri, Nebraska, South Dakota, and Texas would potentially lose an average of 37%, 38%, 30%, 56%, 61%, and 60% of their grain sorghum yield with no weed control, and have a corresponding annual monetary loss of US $19 million, 302 million, 7 million, 32 million, 25 million, and 314 million, respectively. The overall average yield loss due to weed interference was estimated to be 47% for this grain sorghum-growing region. Thus, US farmers would lose approximately 5,700 million kg of grain sorghum valued at approximately US $953 million annually if weeds are not controlled. With each dollar invested in weed management (based on estimated weed control cost of US $100 ha−1), there would be a return of US $3.80, highlighting the return on investment in weed management and the importance of continued weed science research for sustaining high grain sorghum yield and profitability in the United States.