Zahoor A. Ganie

Acetyl-CoA carboxylase (ACCase)-inhibiting herbicides are primarily applied for controlling grass weeds in broadleaf crops. These herbicides are foliar-active, providing minimal residual weed control. This review aims to summarize 1) the history and use of ACCase-inhibiting herbicides in the United States; 2) ACCase-inhibitor-resistant weeds, their mechanisms of resistance, and management strategies; and 3) the future of ACCase-inhibiting herbicides. Herbicides that inhibit ACCase belong to three chemical families: aryloxyphenoxypropionates, cyclohexanediones, and phenylpyrazoles. They function by inhibiting the enzyme ACCase activity, thereby blocking the first step in de novo fatty acid biosynthesis and thus preventing the production of phospholipids and essential secondary metabolites in susceptible plants. Diclofop-methyl was the first ACCase inhibitor discovered in 1975, and commercialized in 1982 in the United States. Pinoxaden was the last herbicide to be commercialized in 2005. As of 2025, a total of 51 grass weed species have been documented as being resistant to ACCase-inhibiting herbicides worldwide, including 16 in the United States. The resistance in these weeds is attributed to both target-site and non–target site mechanisms. Mixing ACCase-inhibiting herbicides with auxinic herbicides can reduce grass weed control due to antagonistic interactions. Therefore, selecting an appropriate tank-mix partner with an ACCase inhibitor is crucial for achieving broad-spectrum weed control, or a dual-tank precision sprayer could be used. Clethodim is the most widely used ACCase-inhibiting herbicide, with 920,339 kg applied to approximately 16% of soybean crops planted in the United States in 2023, at an average application rate of 179 g ha ^‒1 . A recent discovery, metproxybicyclone, will be the first carbocyclic aryl-dione herbicide from a new ACCase inhibitor family. This novel herbicide will be applied postemergence to control sensitive and ACCase inhibitor-resistant grass weeds in broadleaf crops. Continued research efforts are focused on discovering new ACCase-inhibiting herbicides capable of controlling ACCase inhibitor-resistant grass weeds.

Alabama, located in the northern subtropics, is the third‐largest producer of peanut [ Arachis hypogaea (L.)] in the United States. Historically, herbicides have been the primary means of weed control in peanut. However, increasing cases of herbicide‐resistant weeds and a lack of commercially available herbicide‐tolerant technology have limited the herbicide options for weed control in this crop. There is an urgent need to integrate non‐chemical tools to prolong the effectiveness of the existing weed management program in peanut. A 2‐year study in a split‐split plot design was conducted at the Wiregrass Research and Extension Center, Alabama, for investigating integrative and individual effects of row orientation, mulch, and row spacing, in conjugation with a uniform, standard herbicide program, on weed control and yield in peanut. In this study, crop rows planted in east‐west orientation allowed least weed emergence in both years, closely followed by the northeast‐southwest (NE‐SW), as compared to other row orientations. However, the NE‐SW orientation yielded greatest across the years. Row spacing did not influence weed density but affected weed biomass by influencing canopy closure timing as revealed by leaf area index and normalized difference vegetation index (NDVI) data. Mulching influenced both weed density and biomass, especially early in the season. Based on the current study, the NE‐SW row orientation along with mulch or cover optimized early‐season weed suppression and yield in Alabama peanut fields.

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.

Glyphosate is the most widely used herbicide in the United States; however, concern is escalating about increasing residues of glyphosate and its metabolite aminomethylphosphonic acid (AMPA) in soil. There is a lack of scientific literature examining the response of cover crops to soil residues of glyphosate or AMPA. The objectives of this study were to evaluate the impact of glyphosate or AMPA residues in silty clay loam soil on emergence, growth, and biomass of cover crops, including cereal rye, crimson clover, field pea, hairy vetch, and winter wheat, as well as their germination in a 0.07% (0.7 g L^–1) solution of AMPA or glyphosate. Greenhouse studies were conducted at the University of Nebraska–Lincoln to determine the dose response of broadleaf and grass cover crops to soil-applied glyphosate or AMPA. The results indicated that soil treated with glyphosate or AMPA up to 105 mg ae kg^–1 of soil had no effect on the emergence, growth, above-ground biomass, and root biomass of any of the cover crop species tested. To evaluate the impact of AMPA or glyphosate on the seed germination of cover crop species, seeds were soaked in Petri plates filled with a 0.7 g L^–1 solution of AMPA or glyphosate. There was no effect of AMPA on seed germination of any of the cover crop species tested. Seed germination of crimson clover and field pea in a 0.7 g L^–1 solution of glyphosate was comparable to the nontreated control; however, the germination of cereal rye, hairy vetch, and winter wheat was reduced by 48%, 75%, and 66%, respectively, compared to the nontreated control. The results suggested that glyphosate or AMPA up to 105 mg ae kg^–1 in silt clay loam soil is unlikely to cause any negative effect on the evaluated cover crop species.

Herbicide resistance has emerged globally as a serious threat to profitable crop production. FMC promotes integrated weed management approaches including responsible use of existing herbicides, use of non‐herbicide weed control tools, awareness about herbicide resistance issues, and support to herbicide resistance management initiatives. FMC is dedicated to developing sustainable weed control solutions through the discovery of new herbicides with novel sites‐of‐action, effective formulations, advanced application technology, and proactive monitoring for herbicide resistance. © 2020 Society of Chemical Industry

Giant ragweed is one of the most competitive annual broadleaf weeds in corn and soybean crop production systems in the United States and eastern Canada. Management of giant ragweed has become difficult due to the evolution of resistance to glyphosate and/or acetolactate synthase (ALS)-inhibitor herbicides and giant ragweed’s ability to emerge late in the season, specifically in the eastern Corn Belt. Late-season herbicide application may reduce seed production of weed species; however, information is not available about late-season herbicide applications on giant ragweed seed production. The objective of this study was to evaluate the effect of single or sequential late-season applications of 2,4-D, dicamba, glyphosate, and glufosinate on inflorescence injury and seed production of glyphosate-resistant (GR) giant ragweed under greenhouse and field conditions (bare ground study). Single and sequential applications of glufosinate resulted in as much as 59 and 60% injury to giant ragweed inflorescence and as much as 78 and 75% reduction in seed production, respectively, under field and greenhouse conditions. In contrast, single or sequential applications of 2,4-D or dicamba resulted in ≥ 96% inflorescence injury and reduction in seed production in the field as well as in greenhouse studies. The results indicated that 2,4-D or dicamba are effective options for reducing seed production of glyphosate-resistant giant ragweed even if applied late in the season. Targeting weed seed production to decrease the soil seedbank will potentially be an effective strategy for an integrated management of GR giant ragweed.

Glyphosate and 2,4-D have been commonly used for control of common and giant ragweed before planting of corn and soybean in the midwestern United States. Because these herbicides are primarily applied in early spring, environmental factors such as temperature may influence their efficacy. The objectives of this study were to (1) evaluate the influence of temperature on the efficacy of 2,4-D or glyphosate for common and giant ragweed control and the level of glyphosate resistance and (2) determine the underlying physiological mechanisms (absorption and translocation). Glyphosate-susceptible (GS) and glyphosate-resistant (GR) common and giant ragweed biotypes from Nebraska were used for glyphosate dose–response studies, and GR biotypes were used for 2,4-D dose–response studies conducted at two temperatures (day/night [d/n]; low temperature [LT]: 20/11 C d/n; high temperature [HT]: 29/17 C d/n). Results indicate improved efficacy of 2,4-D or glyphosate at HT compared with LT for common and giant ragweed control regardless of susceptibility or resistance to glyphosate. The level of glyphosate resistance decreased in both the species at HT compared with LT, primarily due to more translocation at HT. More translocation of 2,4-D in GR common and giant ragweed at HT compared with LT at 96 h after treatment could be the reason for improved efficacy. Similarly, higher translocation in common ragweed and increased absorption and translocation in giant ragweed resulted in greater efficacy of glyphosate at HT compared with LT. It is concluded that the efficacy of 2,4-D or glyphosate for common and giant ragweed control can be improved if applied at warm temperatures (29/17 C d/n) due to increased absorption and/or translocation compared with applications during cooler temperatures (20/11 C d/n).