Yellow toadflax is an invasive perennial broadleaf weed that negatively affects forage production and wildlife habitat. Few herbicides effectively manage this weed. Glyphosate is a nonselective herbicide that can help manage yellow toadflax but is rarely used in pasture/rangeland because it may injure desirable vegetation. The effectiveness of wiper-applied glyphosate followed by (fb) applications of either chlorsulfuron or picloram was evaluated on yellow toadflax grown in a greenhouse. Glyphosate was applied with a wiper at 0% or 50% diluted concentrate. Chlorsulfuron (26 g ai ha−1) was applied alone or immediately after the wiper application of glyphosate. Picloram (560 g ae ha−1) was applied in a similar manner. At 3 mo after herbicide treatments, estimates of injury to yellow toadflax were greatest with glyphosate, glyphosate fb chlorsulfuron, and glyphosate fb picloram (77% to 86%) compared with chlorsulfuron or picloram applied alone (52% to 56%). The response of subsequently harvested biomass was not different after herbicide treatments. One month after treatment, flowering and regrowth of biomass and root biomass were quantified. Flowering, regrowth, and root biomass demonstrated the greatest (>50%) recovery with wiper-applied glyphosate and wiper-applied glyphosate fb broadcast-applied chlorsulfuron or picloram compared with <50% recovery with broadcast applications of chlorsulfuron or picloram. The results of the experiment suggest that wiper-applied glyphosate fb broadcast applications of chlorsulfuron or picloram can help manage yellow toadflax regrowth compared with single herbicide treatments.

Bahiagrass, guineagrass, and vaseygrass are dominant weeds in bermudagrass pastures. Chemical control of these weeds is difficult, as some herbicides damage bermudagrass. The objectives of this study were to assess the effect of glyphosate and glyphosate mixes with imazapic and nicosulfuron + metsulfuron on bahiagrass control and to evaluate the effect of glyphosate and/or imazapic and nicosulfuron + metsulfuron on guineagrass and vaseygrass control under greenhouse conditions. Bahiagrass field trials were conducted in Citra and Ona, FL, in 2016 and 2018, respectively, while greenhouse experiments were conducted in Ona in 2017 and 2018. Glyphosate tank mixes reduced bahiagrass biomass in Ona, whereas at Citra, biomass reduction did not differ between treatments, although visual estimates of control were lowest with glyphosate at 0.28 kg ae ha−1. Results from the greenhouse experiment show that 0.38 and 0.50 kg ae ha−1 of glyphosate were needed to achieve 80% (ED80) control at 30 d after treatment (DAT), whereas 0.60 and 0.47 kg ae ha−1 were required to reduce 80% biomass of guineagrass and vaseygrass at 60 DAT, respectively. Vaseygrass needed lower imazapic rates (0.05 and 0.19 kg ae ha−1) for ED80 control (visual estimates) and biomass reduction, respectively, whereas guineagrass required higher doses (0.31 and 0.28 kg ae ha−1 for visual estimates of control and biomass reduction, respectively). Glyphosate at 0.56 kg ae ha−1, glyphosate + imazapic, or nicosulfuron + metsulfuron reduced guineagrass biomass, whereas imazapic only, glyphosate tank mixes, and nicosulfuron + metsulfuron resulted in the highest vaseygrass biomass reduction. Glyphosate and glyphosate tank mixes were consistent in controlling all grasses, yet imazapic was effective at higher rates for guineagrass.

A survey was conducted among teak and melina growers across Costa Rica to assess their perceptions of problematic weed species and to document current weed management practices in forest plantations. A total of 180 farmers were selected from six provinces, yielding an 87% response rate. Results revealed that 47% of respondents had established plantations on formerly forested land, while 43% did so on previously used pastureland. Most farmers employed an integrated approach toward weed management that included manual, mechanical, and chemical methods. The most problematic species cited most frequently included coyol palm, jaraguagrass, orchid vine, raspa guacal, and arrocillo. Herbicide use was widespread, with glyphosate, metsulfuron-methyl, and paraquat being the most common active ingredients, typically applied singly, in mixtures, or sequentially. The findings reveal a heavy reliance on only three herbicides and highlight the need for targeted control of species in the Poaceae family and climbing vines. This work contributes valuable insights into weed dynamics in tropical forest plantations and emphasizes the need for region-specific and sustainable management strategies to mitigate potential productivity constraints and reduce reliance on herbicides.

Effective waterhemp management in crop rotations that include sugar beet requires a proactive approach, starting with robust weed management in the preceding crop. Sugar beet is vulnerable to weeds due to its poor competitiveness during its early growth stages and a limited availability of effective herbicide options within this rotation. This research aimed to evaluate multi-tactic weed management strategies, including planting soybean in narrow rows with low- and high-input treatments, and a high-input treatment plus harvest-time weed seed control (HWSC) simulation, on waterhemp control and seed production in soybean, and their effects on waterhemp density in the following sugar beet crop. Field experiments were conducted from 2021 to 2023 in Franklin, Moorhead, and Rosemount, Minnesota. Soybean planted in narrow rows closed the canopy earlier at Franklin in 2021 and at Moorhead in 2022. Soybean row spacing did not affect waterhemp control, density, biomass, or seed production at any site-year. A high-input treatment consisting of flumioxazin applied preemergence followed by (fb) an early postemergence application of lactofen + acetochlor fb a late-postemergence application of 2,4-D + glyphosate provided ≥95% waterhemp control at harvest at all site-years and seed production was reduced to 0 seeds m−2 at Franklin and Rosemount. At those locations, waterhemp control at harvest was comparable among all high-input herbicide treatments. Soybean planted in narrow rows yielded 9.4% and 18.5% more than soybean planted in wide rows at Franklin and Rosemount, respectively, while no yield difference was observed at Moorhead. Waterhemp emergence in the subsequent season’s sugar beet crop fell by 72% to 92% at the Franklin site in 2022, Moorhead in 2023, and Rosemount in 2023 after high-input herbicide treatments. However, adding HWSC to a high-input treatment did not result in a further reduction of waterhemp density. In this research, 1 yr of effective waterhemp control with high-input herbicide treatments in soybean reduced waterhemp emergence in the following season’s sugar beet crop.

A new encapsulated saflufenacil formulation has been developed and premixed as a single product with pyroxasulfone to provide control of small-seeded annual grass and broadleaf weeds and to extend the application window to early postemergence when applied to field corn. Pyroxasulfone + encapsulated saflufenacil applied preemergence alone and in mixtures with other herbicides were examined for crop response and weed control efficacy. We hypothesized that applying pyroxasulfone + encapsulated saflufenacil with a tank-mix partner would expand the spectrum of weed species that can be controlled and improve overall weed control efficacy compared to pyroxasulfone + encapsulated saflufenacil applied alone. Six field experiments were completed at three locations in southwestern Ontario in 2022 and 2023. Pyroxasulfone + encapsulated saflufenacil was applied alone, at 146 g ai ha−1 (pyroxasulfone 90 g ai ha−1, saflufenacil 56 g ai ha−1) or 245 g ai ha−1 (pyroxasulfone 150, saflufenacil 95 g ai ha−1), and with the following herbicide partners: atrazine, dicamba, or mesotrione + atrazine. All herbicide treatments were applied prior to corn and weed emergence. Weed control, density and biomass, and corn injury and yield were assessed. All pyroxasulfone + encapsulated saflufenacil treatments caused no injury to corn. At 8 wk after emergence (WAE) pyroxasulfone + encapsulated saflufenacil (245 g ai ha−1) controlled common lambsquarters, redroot pigweed, and foxtail species by 42%, 59%, and 41%, respectively. Applications of pyroxasulfone + encapsulated saflufenacil (146 or 245 g ai ha−1) with dicamba or mesotrione + atrazine improved common lambsquarters and redroot pigweed control at 8 WAE compared with pyroxasulfone + encapsulated saflufenacil applied alone. Pyroxasulfone + encapsulated saflufenacil (146 or 245 g ai ha−1) applied with dicamba or mesotrione + atrazine provided similar control of common lambsquarters, redroot pigweed, and foxtail species to that of S-metolachlor/atrazine/mesotrione/bicyclopyrone, which is a standard herbicide used to control these weeds. Corn yield for all pyroxasulfone + encapsulated saflufenacil herbicide mixtures was similar to that of the weed-free control and the standard herbicide.

Weed management in peanut primarily relies on intensive herbicide programs. Integrating cereal rye as a cover crop may reduce herbicide input without compromising weed control. Field experiments were conducted to evaluate cereal rye termination management and herbicide programs in peanut. Main plot treatments included a winter fallow control and four cereal rye termination scenarios: 1) early termination 28 d before peanut planting (DBP) with residue rolled flat; 2) early termination 28 DBP with residue left standing; 3) late termination 14 DBP with residue rolled flat; or 4) late termination 14 DBP with residue left standing. Subplot treatments consisted of four herbicide programs: 1) preemergence + early postemergence + mid-postemergence herbicides; 2) preemergence + mid-postemergence herbicides; 3) early postemergence + mid-postemergence herbicides; and 4) a nontreated control. Early cereal rye termination (28 DBP), whether rolled or standing, reduced Palmer amaranth density by 36% to 48% without preemergence herbicides and by 36% to 50% when preemergence herbicides (fluridone or flumioxazin) were applied. Sicklepod density was unaffected by early termination. In contrast, late termination reduced sicklepod density by 47% to 50% and Palmer amaranth density by 64% to 86% relative to the winter fallow control at 28 d after preemergence application. Across all treatments, cereal rye reduced Palmer amaranth and sicklepod biomass by 63% to 67% and 63% to 65%, respectively, 28 d after mid-postemergence herbicides were applied. However, standing cereal rye residue reduced peanut yield compared to rolled residue and the winter fallow. Late-terminated, rolled cereal rye residue combined with reduced herbicide programs (preemergence + mid-postemergence or early postemergence + mid-postemergence) provided weed control and yield comparable to the intensive herbicide program (preemergence + early postemergence + mid-postemergence) in winter fallow control. Based on these findings, late-terminated, rolled cereal rye has the potential to reduce herbicide input while maintaining peanut yield and effective weed suppression.

Volunteer corn is a problem weed in sorghum fields rotated with corn. The commercial availability of imazamox-resistant (igrowth®) and quizalofop-resistant (Double Team™) sorghum allows the use of imazamox and quizalofop, respectively, for controlling grass weeds; however, information is not available regarding their efficacy for control of volunteer corn. The objective of this study was to evaluate the efficacy of imazamox and quizalofop for control, density and biomass reduction of glufosinate/glyphosate-resistant corn volunteers in imazamox- and quizalofop-resistant sorghum. Two separate field experiments were conducted near Clay Center, NE, in 2023 and 2024. Imazamox applied early postemergence (E-POST) and late postemergence (L-POST) (53 and 79 g ai ha–1) controlled up to 98% and 89% of corn volunteers 28 d after application (DAA) in 2023 and 2024, respectively, in igrowth® sorghum. Similarly, quizalofop applied E-POST and L-POST (58 and 73 g ai ha–1) provided 98% and 99% control of volunteer corn in 2023 and 2024, respectively, in Double Team™ sorghum. Quizalofop reduced volunteer corn density (0 to 0.2 plants m–1) and biomass (0 to 13 g m–2) compared to nontreated control in both years. The results suggest that imazamox and quizalofop could be used as POST herbicides for control of glufosinate/glyphosate-resistant corn volunteers in imazamox- and quizalofop-resistant sorghum, respectively.

In southern Australia, sowthistle and prickly lettuce are difficult to control when they grow among pulse crops because few postemergence herbicide options exist to control them and resistance to herbicides that inhibit acetolactate synthase (ALS) has become widespread. The introduction of new herbicide-tolerance traits to these crops is one possible avenue for improving control options. This study evaluated ways to control ALS inhibitor–resistant common sowthistle and prickly lettuce in a novel breeding line of metribuzin-tolerant lentil being developed in Australia. Field experiments conducted over 3 site-years in South Australia aimed to evaluate various rates and application timings of metribuzin, with and without the postemergence addition of diflufenican, compared to preemergence terbuthylazine applications. Herbicide treatments achieved significant levels of control of both common sowthistle and prickly lettuce compared to untreated control plots, and there was no negative effect of these treatments on lentil establishment or yield, despite two sites experiencing environmental conditions that were conducive to crop damage by the herbicides. Greater control was obtained when higher rates of metribuzin were applied post-sowing preemergence and after the postemergence application of diflufenican. Terbuthylazine treatments also performed well compared to the untreated control; however, terbuthylazine was not as effective as the higher rates of metribuzin. These results indicate that the introduction of a metribuzin-tolerant lentil cultivar will provide an effective in-crop broadleaf weed control option while also avoiding some of the damage associated with currently available herbicides.

Quinclorac is a selective postemergence herbicide with activity on both grasses and broadleaf weeds, including the problematic field bindweed, making it useful in systems with mixed weed populations. Field studies conducted from 2021 to 2022 in California, Michigan, New Jersey, New York, and Oregon assessed both crop safety and weed control efficacy for potential registration in grapes. Quinclorac was applied as a directed spray at 0.42 and 0.84 kg ai ha−1 at three timings: 90 d before harvest (Timing A), 60 d before harvest (Timing B), and post-harvest (Timing C). No grapevine injury was observed in California or Oregon. However, injury occurred in Michigan, New Jersey, and New York, with maximum ratings up to 32%, though severity varied by year and location. Mixed-effects modeling showed that cumulative rainfall and soil clay-plus-organic matter (COM) content explained 52% of the variation in injury (P < 0.001), with injury increasing as rainfall and COM content rose. Despite visible symptoms at some low-COM, high-rainfall sites, quinclorac had no significant effect on yield, berry size, or dormant pruning weights. Field bindweed control was consistently improved by quinclorac, particularly when a post-harvest application was included. Under the evaluated rates and timings, quinclorac posed an unacceptable risk of grapevine injury in many environments and is not currently suitable for use in grapes. Future work should focus on identifying management practices to mitigate the potential for injury.

Late-season escapes of Palmer amaranth and waterhemp (both are Amaranthus species) pose a significant challenge in cotton production due to their high fecundity, herbicide resistance, and ability to replenish the weed seedbank at harvest. While harvest weed seed control (HWSC) has been adopted in grain systems, its feasibility in cotton remains unknown due to differences in cotton harvesting equipment design. Therefore, this study aimed to determine the fate of Amaranthus spp. seeds during harvest with cotton pickers and stripper harvesters, and evaluated the efficacy of an impact mill to destroy a range of weed seeds present in different types of cotton debris. Along with the seed cotton, cotton strippers removed 52% of the Amaranthus seeds, compared with just 7% with pickers, which are then cleaned at the cotton gin. About 85% of the seeds were retained on the plant after harvest by the pickers, and about 15% by the strippers. Seeds shattered to the ground accounted for 8% with pickers and 18% with strippers. Additionally, the cotton stripper’s field cleaner mechanism removed 15% of the weed seeds. Together, seeds collected in seed cotton, retained on the plant, or separated by field cleaners (in strippers) represent points for HWSC implementation. Different types of cotton debris were then run through a stationary weed-seed impact mill with a known number of seeds for seven weed species to determine seed destruction efficacy. The stem debris had a 29% moisture content, which is too high for the impact mill and caused mill clogging; however, seed kill levels of 98% were achieved in bur debris and gin debris types, values similar to those reported in grain systems. Together, these findings provide a framework for incorporating HWSC practices into cotton, offering growers and processors a way to reduce weed seedbank inputs.

Recent reports of glyphosate-resistant (GR) waterhemp pose serious concerns among crop producers in New York. Field experiments were conducted in 2019 and 2020 near Waterloo, New York, to evaluate the effectiveness of preemergence, postemergence, preemergence followed by (fb) postemergence, and preemergence herbicides fb row cultivation (RC) to control glyphosate-resistant (GR) waterhemp in dicamba-resistant (DR) soybean. In 2019, all two-pass herbicide treatments resulted in significantly reduced GR waterhemp densities (2 to 13 plants m−2) compared with nontreated plots (160 plant m−2) at 8 wk after preemergence/2 wk after postemergence, reductions in shoot dry biomass (85% to 99% of nontreated), and greater soybean grain yields (2,659 to 2,936 kg ha−1). In addition, flumioxazin, acetochlor, chlorimuron + flumioxazin + metribuzin, acetochlor + fomesafen + metribuzin, carfentrazone + sulfentrazone + metribuzin, and S-metolachlor + sulfentrazone + metribuzin applied preemergence resulted in significant reductions in GR waterhemp density (3 to 19 plants m−2) and shoot dry biomass (60% to 98% of nontreated). In 2020, most preemergence (except cloransulam), postemergence only, and preemergence fb postemergence herbicide application strategies resulted in lower densities of GR waterhemp (1 to 46 plants m−2) compared with nontreated plots (104 plants m−2) at 8 wk after preemergence/2wk after postemergence and lower shoot dry biomass (66% to 99% of nontreated). All two-pass strategies as well as metribuzin, acetochlor + fomesafen + metribuzin, carfentrazone + sulfentrazone applied preemergence resulted in higher grain yields (3,343 to 4,244 kg ha−1). These results conclude that two-pass strategies tested in this research can consistently provide effective control of GR waterhemp in DR soybean in New York.

The rapid spread of herbicide resistance in weeds, driven by gene flow through multiple pathways, poses an increasing challenge for agricultural systems. This review summarizes the extent and distance of pollen- and seed-mediated gene flow (PMGF and SMGF, respectively) in selected self-pollinated weeds and the environmental factors that influence PMGF. A comprehensive literature review was focused on assessing PMGF patterns, dispersal mechanisms, and influencing factors across self-pollinated weed species. Statistical analyses were conducted to evaluate correlations between PMGF and environmental variables, including temperature, precipitation, humidity, and elevation. Self-pollinated weeds in the Asteraceae family show the highest PMGF (average 10.63%), with common groundsel showing 24% at 0.5 m from the pollen source. Solanaceae and Chenopodiaceae are plant families with the second and third highest PMGF (average 10.00% and 1.58%, respectively). Within Solanaceae, eastern black nightshade exhibited the maximum PMGF (17%), whereas in Chenopodiaceae, magenta spreen showed the highest gene flow, reaching 3% at 15 m from the pollen source. In contrast, the lowest mean PMGF was observed in Poaceae and Brassicaceae (average 1.87% and 0.33%, respectively). Furthermore, among environmental variables, only temperature showed a significant correlation (P < 0.05). Due to the limited number of studies, this correlation should be viewed cautiously, as it likely reflects general patterns rather than a causal link to PMGF. Bold-seeded grasses such as oat may disperse seeds at low frequency (14-18%), however, light-seeded species such as horseweed can disperse as high as 99% of their seeds. Understanding gene flow in self-pollinated weeds with high fecundity is vital to limiting herbicide resistance spread in such species.

Wild rice is a high-value specialty crop in California. Weeds are an important pest issue in this crop, yet to date, only carfentrazone is registered for weed control in this crop. Herbicide field trials were conducted in 2022 and 2023 in Shasta and Yolo counties, California, in support of the IR-4 project’s mission to register new pesticides for specialty crops. Herbicides tested for efficacy and crop safety included cyhalofop-butyl, florpyrauxifen-benzyl, penoxsulam, propanil, and triclopyr at two application rates each, as well as carfentrazone applied at the labeled rate. At all sites, weed control was acceptable with most treatments and comparable to that of carfentrazone. Generally, florpyrauxifen-benzyl, penoxsulam, and triclopyr provided the greatest broad-spectrum weed control. In particular, uncommon weeds such as common spikerush and longleaf pondweed (Shasta County sites in 2022 and 2023, respectively) were controlled well with these herbicides. Propanil was also very effective against these two species, yet it provided only up to 25% control of ricefield bulrush. Crop response to herbicides was variable. Carfentrazone, cyhalofop-butyl, florpyrauxifen-benzyl, and propanil all caused minor and transient injury to the wild rice, characterized by chlorosis, leaf burn, and stunting. Florpyrauxifen-benzyl and triclopyr also caused some leaf deformation, which the wild rice did not recover from. The most significant crop injury was caused by penoxsulam, resulting in severe or complete stand loss at the low and high rates, respectively, across all site-years. Triclopyr also caused unacceptable lodging at both rates at all sites, significantly reducing yield at the higher rate. Crop yields in noninjured plots were similar to those from the untreated control and carfentrazone-treated plots, although the higher rate of florpyrauxifen-benzyl did reduce yields somewhat. These data provide important crop-safety information for wild rice and will inform further herbicide program research toward potential registration for wild rice in California.

Palmer amaranth is an increasing concern for producers in the northeastern United States. A new Palmer amaranth population (NY_PA) was identified in a soybean field in Ontario County, New York, in 2024. The main objectives of this research were to 1) confirm whether this NY_PA population is resistant to glyphosate and atrazine, and 2) determine the effectiveness of various postemergence herbicides alone or in mixtures to control it. Along with the NY_PA population, two previously known glyphosate-resistant Palmer amaranth populations from Connecticut (CT_PA) and Kansas (KS_PA), and a known glyphosate-susceptible population from Alabama (AL_SUS) were also evaluated. Results from the quantitative polymerase chain reaction assay revealed that the NY_PA population had an average of 180 copies of the 5-enolpyruvylshikimate-3-phosphate synthase (EPSPS) gene with a single EPSPS gene copy in the AL_SUS population. A greenhouse dose-response study revealed that the NY_PA and CT_PA populations had 7-fold to 11-fold resistance to atrazine. Nearly all postemergence herbicides tested, including 2,4-D, dicamba, saflufenacil, glufosinate, and lactofen alone or in mixtures with 2,4-D, dicamba, and glufosinate, provided effective control (90% to 100%) of Palmer amaranth weeds collected in Connecticut, Kansas, and New York. All these postemergence herbicides, alone or in mixtures, reduced shoot dry biomass of all three populations by 82% to 97% compared with plants in nontreated control plots. These results confirm the first report of Palmer amaranth populations from New York and Connecticut with resistance to multiple herbicides (glyphosate and atrazine). Effective postemergence herbicides tested in this research can be used to manage these Palmer amaranth populations.

The recommended method of control for glyphosate-resistant (GR) Italian ryegrass in Mississippi is to apply residual herbicides in the fall; however, these treatments may negatively affect rice performance. This study was conducted to evaluate rice performance following fall-applied treatments of residual herbicides + flumioxazin at different rates. Pooled over with and without flumioxazin and herbicide rates, clomazone and dimethenamid-P caused <10% injury 28 d after emergence. Acetochlor delayed rice maturity by 2 d to clomazone, dimethenamid-P, and flumioxazin. Rice density was reduced ≥4 plants m−2 following fall-applied acetochlor and dimethenamid-P compared to nontreated plants. Rough rice yields were reduced by ≥670 kg ha−1 with fall-applied acetochlor alone and dimethenamid-P compared to nontreated plants. Acetochlor should not be used as a fall-applied treatment in areas where rice is scheduled to grow the following season. Given current label restrictions and rice injury caused by acetochlor and dimethenamid-P, clomazone remains the only viable option for controlling GR Italian ryegrass where rice is scheduled to be planted the following spring.