Glyphosate has been a cornerstone of weed management in Illinois corn and soybean production, supporting conservation tillage, lowering production costs, and stabilizing yields. Growing regulatory scrutiny, litigation, herbicide resistance, and public concern have raised the possibility of restrictions or a complete ban on glyphosate use. This paper evaluates the farm-level revenue consequences of a hypothetical glyphosate prohibition in Illinois agriculture. Using a staged analytical framework, we first quantify baseline glyphosate use and expenditures, then draw on the agronomic and economic literature to estimate yield elasticities for corn and soybean under a complete ban assuming no substitution (where a yield elasticity measures the percentage change in crop yield associated with a one-percent change in glyphosate use, capturing the sensitivity of production to its removal). We subsequently examine producer substitution toward alternative weed-management programs and quantify the resulting changes in production costs and farm revenues under maintained yields. Finally, we extend the analysis to scenarios in which increased demand raises substitute input prices and yields decline modestly due to imperfect weed-control performance. The results indicate that, for corn and soybean producers combined, the statewide loss will be in the order of $300-609 million per year, i.e. about a 1.8-3.6% revenue loss. Our manuscript is the first one to offer a transparent, evidence-based assessment of how glyphosate removal would affect farm revenues through yield and cost channels.

Timely soybean planting is important for maximizing yield, with farmers tending to plant their crops earlier. However, when a soybean crop is planted ultra-early (before April 15th in Ohio), seedlings are exposed to cold and moist conditions that can lead to a smaller plant population, delayed canopy closure, and reduced ability to compete with weeds. The objective of this study was to evaluate herbicide treatments for their effect on weed development and soybean yield when the crop was planted ultra-early (before April 15) and at a normal time (early to mid-May in Ohio). Weed biomass was significantly reduced when the crop was treated at early postemergence. However, preemergence followed by early postemergence herbicide applications were generally less effective at suppressing weeds than treatments that included an early postemergence and late postemergence application, for which weed density was reduced and weed control was improved later in the season. In 2024, when the number of soybean plants was very low due to freeze damage, an early postemergence application of dicamba + glyphosate and a late postemergence application of glyphosate + glufosinate + S-metolachlor resulted in the greatest weed control and yield from the crop that was planted ultra-early. The results from this study indicate that when soybean was planted ultra-early, treatments that included two postemergence applications, particularly those that included a residual herbicide applied at late postemergence, were better suited to maintain weed suppression later in the season and protect soybean yield potential when the soybean plant population was very low and pressure from grass weeds was high.

Glufosinate is a key postemergence herbicide in U.S. soybean production, particularly where resistance to glyphosate and inhibitors of acetolactate synthase is widespread. A 25-question survey of soybean growers, agronomists, and industry professionals in Arkansas and Wisconsin was conducted in Fall 2022 to characterize glufosinate use patterns, weed management challenges, and stakeholder perceptions. Palmer amaranth was reported as the most problematic weed in Arkansas (97% of respondents), and waterhemp was most frequently reported in Wisconsin (92%). Suspected glyphosate resistance was widely reported (97% in Arkansas, 88% in Wisconsin), and suspected glufosinate resistance was reported by 37% of Arkansas respondents and by 3% of Wisconsin respondents. Eighty-four percent of Arkansas respondents reported integrating glufosinate into their weed management programs, as did 53% of Wisconsin respondents, and most respondents said they used it to target broadleaf weeds ≤15 cm tall. Carrier volumes were 103 to 140 L ha−1 (chosen by 75% of Arkansas respondents), and 150 to 187 L ha−1 (chosen by 86% of respondents from Wisconsin). Arkansas respondents most frequently reported using glufosinate in sequential first and second postemergence applications (62%). In Wisconsin, glufosinate use was reported mostly only as a first postemergence application (37%), followed closely by sequential use in the first and second postemergence applications (34%). Weed size, followed by carrier volume and air temperature, were ranked as the most important factors affecting glufosinate performance. Ammonium sulfate was the most used adjuvant (45% in Arkansas; 67% in Wisconsin), and spray water quality was rarely tested. Frequently reported tank-mix partners included glyphosate and inhibitors of protoporphyrinogen oxidase in Arkansas and synthetic auxins and clethodim in Wisconsin. Extension efforts should emphasize applying glufosinate to small weeds (<10 cm in height), optimizing application technology and spray solution characteristics (nozzle, carrier volume, water quality/adjuvant selection), and spraying under favorable environmental conditions. Improving application consistency can reduce weed escapes and repeat postemergence applications, thereby lowering selection pressure and preserving glufosinate as an important postemergence option.

The use of unmanned aerial vehicles (UAVs) shows promise as a potential new way to apply herbicides; however, relatively few studies have been conducted to determine how UAV application parameters influence spray deposition and weed control. Separate experiments were conducted in soybean fields in 2023 and 2024 to 1) compare weed control, spray coverage, and uniformity, and off-target movement between a DJI Agras T40 unpiloted vehicle and ground-based sprayers; and 2) determine the effects of application speed, spray height, and spray volume on spray coverage and waterhemp control with a UAV. Ground-based sprayers consistently provided greater and more uniform spray coverage than the UAV and resulted in more consistent waterhemp control across the swath width. Normalized coverage data indicated greater proportional off-target spray movement with the UAV, although absolute off-target coverage did not differ between application methods. In the second experiment, a variety of different UAV spray application parameters were assessed for their effects on spray coverage and waterhemp control following applications of glufosinate. Coverage in the center of the swath was improved at an application speed of 3.5 m s−1 compared with 7 m s−1, while increasing the height of application above the soybean canopy from 3 m to 4.5 m resulted in lower waterhemp control. Overall, results from this research indicate that herbicides applied with a UAV can provide effective weed control under optimized operating conditions but generally require narrower swath widths, careful management of application parameters, and additional drift mitigation practices.

The U.S. Environmental Protection Agency has proposed increased restrictions and lower application rates for atrazine. Corn growers need to have options for weed control, and increased scrutiny of atrazine may limit effective herbicides that inhibit the photosystem II within weeds. One alternative weed control option is the premixture of amicarbazone and metribuzin. The atrazine label prohibits planting soybean until the following year, limiting producers to replanting corn or grain sorghum after a failed stand. Amicarbazone allows a 4-mo soybean rotation interval, potentially enabling planting of the crop the same season as failed corn. Therefore, research was conducted in 2023 and 2024 in Fayetteville, Arkansas, to evaluate soybean tolerance to an amicarbazone and metribuzin premixture after a simulated failed corn stand. Amicarbazone was applied at 245, 490, and 735 g ai ha−1 alone and in combination with metribuzin at 140, 280, and 420 g ai ha−1. Soybean was planted following at least 1.3 cm of rain (19 to 20 d after application). The label allows amicarbazone and metribuzin to be applied to corn at 336 and 190 g ha−1, respectively, on silt loam soil with organic matter of 1.5% to 2%. The combination of amicarbazone and metribuzin at 735 and 420 g ha−1, respectively, more than twice the labeled rate for corn, induced 61% to 91% soybean injury 14 d after emergence (DAE). When amicarbazone and metribuzin rates were reduced to 245 and 140 g ha−1, respectively, the injury was 4% in both years at 14 DAE. Yield reductions were observed only after treatments with amicarbazone at 735 g ha−1 applied alone or in combination with metribuzin at 420 g ha−1. Overall, crop response and yield reductions should be expected with an amicarbazone and metribuzin premixture at the highest rates used in this study. However, the label for the premixture will not allow these rates to be applied.

Effective weed management is critical to the long-term productivity of organic grain cropping systems. The Cornell Organic Cropping Systems Experiment was initiated in 2005 at the Musgrave Research Farm in Aurora, NY, to compare four organic cropping systems that differed primarily in intensity of mechanical weed management and soil nutrient inputs. A 3-yr rotation of corn (Zea mays L.), soybean [Glycine max (L.) Merr.], and spelt (Triticum spelta L.)/red clover (Trifolium pratense L.) was grown in all systems. The four systems were characterized by High Fertility (red clover green manure, composted poultry manure, and commercial organic fertilizer to reach recommended fertility levels), Low Fertility (no fertility inputs other than the red clover and starter fertilizer for corn), Enhanced Weed Management (fertility management as in Low Fertility with additional tillage and cultivation and a higher spelt seeding density), and Reduced Tillage (primarily ridge tillage with different green manure crops). The experiment included two crop rotation entry points, enabling two of the three crops in the rotation to be grown every year. Results from the first two rotation cycles show that, in most cases, weed abundance and diversity increased during the transition to organic production, especially in the Reduced Tillage system. Perennial weeds increased in corn and soybean in the Reduced Tillage system in the second rotation cycle, which contributed to its poor performance relative to the three other systems. Our results suggest that increased soil disturbance, including tillage and cultivation in corn and soybean, plays an important role in reducing weed populations, whereas high fertility levels may exacerbate weed problems. These findings underscore the importance of balancing weed and nutrient management in enabling sustainable organic grain crop production.

Growers have increasingly adopted the planting of cover crops as a sustainable way to control problematic and herbicide-resistant weeds. Understanding the critical period of crop-weed competition is essential for timely and effective weed management tactics in cropping systems. A 2-yr field experiment was conducted in Alabama to evaluate the effect of a cover crop mixture that included cereal rye, crimson clover, and hairy vetch, and a planting of cereal rye alone on the critical period for weed control (CPWC) in soybean. The experiment was implemented in a split-plot design in which the main plots were cover crop mixture, cereal rye, and winter fallow, and subplots were five durations of weed-free and weed-interference plots. The presence of planting a cover crop mixture and cereal rye delayed the critical timing for weed removal (CTWR) by approximately 2 wk compared with winter fallow. Results in 2019 showed the predicted duration of CPWC following cover crop mixture, cereal rye, and winter fallow was 4.8 wk, 0 wk, and 5.1 wk, respectively. Furthermore, in 2020, the estimated CPWC duration following plantings of a cover crop mixture or cereal rye versus a winter fallow was 1.4 wk, 0.1 wk, and 2.6 wk, respectively. In both years, the plantings of single-species cereal rye resulted in the shortest CPWC due to its early-season weed suppression, while winter fallow plots demonstrated the longest CPWC duration. In conclusion, a shorter duration of CPWC with the incorporation of cover crops could help soybean growers enhance their weed control efforts and provide greater yield protection to soybean.

Preventing white-tailed deer from browsing on crops and resulting in lower crop yields has been a challenge within agriculture for several decades. In an effort to reduce the soybean losses incurred by deer browsing, several wildlife repellents have been commercialized and marketed for use on soybean. Despite the availability of these repellents, limited research has been conducted on their ability to deter deer feeding or their effects on weed control when applied in combination with common herbicides. To narrow this knowledge gap, field experiments were carried out in 2023 and 2024 to evaluate five commercial deer repellent products (Bobbex, Hinder, Liquid Fence, Plantskydd +, and Penergetic bWV) for their ability to reduce deer browsing on soybean. Each product was applied either once, twice, or three times in conjunction with preplant burndown, early postemergence, and late postemergence pesticides, respectively. Regular assessments of deer browsing were conducted at weekly intervals following herbicide applications. At all locations in 2023 and 2024, none of the repellent products, even those that were applied three times sequentially, provided any consistent suppression in deer browsing throughout the growing season. An additional field experiment during both seasons evaluated the effects of common herbicides combined with deer repellents on weed control efficacy and soybean injury. Results from these trials indicate that very few differences in foxtail species, waterhemp, and common cocklebur control and crop injury were observed with any repellent and herbicide combination compared to treatments with postemergent herbicides alone. Overall, the results from these experiments indicate that combining deer repellent products with herbicides in tank mixtures does not result in any increase or decrease in weed control compared with applying herbicides alone. There is also no evidence that these repellent products effectively deter deer when the soybean plant may be most vulnerable.

In the Midwest United States, early soybean planting is becoming more common, but the implications for soil residual herbicide dissipation and optimal application time remain unclear. Earlier planting extends the interval between soil-residual herbicide application at planting and the onset and peak of weed emergence, potentially reducing efficacy through an extended window for dissipation. This study aimed to evaluate the dissipation and weed control efficacy of soil residual herbicides applied at different timings in early planted soybean crops under varying soil conditions. At Arlington, Wisconsin, which has a silt loam soil, herbicide concentrations when soil was sampled, 21 d after the fourth and final application of herbicides, which followed a series of treatments from planting to the V1 growth stage of soybean, were similar across application times, whereas at Brooklyn, Wisconsin, which has a sandy loam soil, herbicide concentrations were usually higher when herbicides were applied later. Despite these differences, weed density at postemergence was similar across application times within each site. However, an additional late postemergence herbicide application was necessary at Brooklyn following the earliest application times in 2022, indicating more rapid herbicide dissipation. Herbicide dissipation and efficacy varied by soil texture. In sandy soils, early applications may lead to reduced control of late-emerging weeds due to rapid dissipation. In contrast, finer-textured soils may allow for more flexible application timing. These insights support site-specific residual herbicide application strategies in early planted soybean systems.

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.

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.

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.

Targeted herbicide applications have the potential to reduce herbicide use but they pose an inherent risk of missing late-season weed escapes. Furthermore, relying on targeted use of residual herbicides may increase weed emergence relative to broadcast applications. Research was conducted over a 3-yr period in Keiser, Arkansas, to compare traditional broadcast applications to targeted postemergence applications of various herbicides to soybean cultivars that are known to be resistant to glyphosate, glufosinate, and dicamba. The herbicide treatment protocol was consistent across treatments with a broadcast-applied preemergence residual, and a postemergence combination that included glufosinate + glyphosate + S-metolachlor followed by glufosinate + acetochlor, applied both via broadcast or targeted at the highest and lowest spray sensitivities of the John Deere See & Spray technology. The soil seedbank was similar at trial initiation across treatments, and there was no increase in the seedbank over 3 yr of broadcast and targeted applications at the highest spray sensitivity. Averaged over application timing, when herbicides were applied at the lowest spray sensitivity the weed density rose from 867 plants ha−1 to 2,870 plants ha−1 in Year 2, to 11,300 plants ha−1 in Year 3. This response is likely due to more Palmer amaranth escapes when the crop was harvested with an average of >1,000 plants ha−1 over the years compared with weed density after herbicides were applied with the highest spray sensitivity and via broadcast. Targeted applications improved profitability by reducing herbicide use and increasing application efficiency, providing an average savings of US$43.22 ha−1 to $129.19 ha−1 relative to broadcast postemergence cost of $227.22 ha−1. The area sprayed was reduced by 20% to 90%, with an average spraying at early postemergence of 41.3% and 57.9% and at mid-postemergence equaling 48.1% and 49.3% when herbicides were applied with the lowest and highest spray sensitivities, respectively. The only difference in the area sprayed between sensitivity settings occurred early postemergence. Based on the results of this experiment, producers could apply postemergence herbicides targeted to weeds that grow with soybean to increase profitability, but the lowest sensitivity resulted in unacceptable increases to the weed seedbank, which could affect management in future years.

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.

Dicamba-resistant soybean was developed and commercialized by Monsanto in 2016, and in recent years, barnyardgrass has become more troublesome for growers who use residual herbicides with dicamba technology. Field studies were conducted from 2019 to 2021 in Stoneville, Mississippi, to evaluate barnyardgrass control after applications of glyphosate or glyphosate + dicamba, when mixed with residual herbicides, and when applied sequentially. In the first field study, glyphosate (1,120 g ae ha−1) and glyphosate + dicamba (560 g ae ha−1) were applied in combination with common residual herbicides. The second field study included an initial treatment with glyphosate (1,120 g ha−1), glyphosate + dicamba (560 g ha−1), and glyphosate + dicamba + S-metolachlor (1,064 g ai ha−1) followed by a sequential treatment of glyphosate or glyphosate + dicamba at 3 and 7 d after an initial herbicide treatment. Results indicated that glyphosate alone provided greater barnyardgrass control than glyphosate + dicamba. Additionally, at 28 d after treatment, pyroxasulfone, pyroxasulfone + fluthiacet, dimethenamid-P, and S-metolachlor did not affect postemergence control of barnyardgrass after glyphosate + dicamba treatments. Furthermore, sequential herbicide treatments of glyphosate or glyphosate + dicamba led to no difference in barnyardgrass control 28 d after the sequential treatment. These results indicate that options exist for adding residual herbicides to glyphosate + dicamba treatments and that sequential treatments of glyphosate or glyphosate + dicamba are important for optimizing barnyardgrass control.

Palmer amaranth and waterhemp are troublesome weeds in U.S. corn, soybean, and cotton production systems. Rapid evolution of resistance to herbicide from multiple sites of action in these species warrant alternate weed control options. Metribuzin applied preemergence can provide effective control of herbicide-resistant Amaranthus species. However, despite its decades of efficacy, many growers remain unaware of its weed control potential or are hesitant to use it due to concerns over crop injury. Field experiments were conducted in 2022 and 2023 in 15 states across the United States to investigate residual control of Palmer amaranth and waterhemp with metribuzin applied preemergence to soybean. Sites had either herbicide-resistant Palmer amaranth or waterhemp as the dominant weed species. Seventeen preemergence treatments were evaluated, including 13 doses of metribuzin (210 to 841 g ai ha-1), a dose of sulfentrazone (420 g ai ha-1), and a dose of S-metolachlor (1,790 g ai ha-1), along with nontreated and a weed-free control plots. Weed control and soybean injury were visually assessed and recorded at 14, 28, and 42 d after application (DAA) of preemergence herbicides. Additionally, weed density, weed biomass, and soybean height were recorded 28 DAA followed by a measure of soybean yield at maturity. Weed control was analyzed as a function of metribuzin dose and environmental factors using a generalized additive model. Crop injury of not more than 5% was predicted even with 841 g ai ha-1 of metribuzin. Metribuzin at 630 g ai ha-1 was more effective than sulfentrazone in delaying weed emergence and reducing weed density, while 315 g ai ha-1 of metribuzin outperformed S-metolachlor in both metrics. Metribuzin doses of 578 to 841 g ai ha-1 provided greater than 95%, 90%, and 80% weed control, respectively, at 14, 28, and 42 DAA. Higher metribuzin doses of 578 to 841 g ai ha-1could be safely to effectively control herbicide-resistant Amaranthus weeds.

Dicamba-resistant (DR) soybean cultivars are essential elements in managing broadleaf weeds in modern production systems. However, limited information is available regarding yield reductions associated with dicamba rates that were previously registered for postemergence weed control and off-label dicamba rates in these cultivars. This study aimed to characterize and quantify the effects of postemergence dicamba applications on two DR soybean cultivars. Field trials were conducted in 2022 and 2023, with dicamba applied at 0 to 1,440 g ae ha⁻¹ during the V5 to V6 stages. Visible injury increased with dicamba rate, reaching 18% (Cultivar A) to 20% (Cultivar B) at 1,440 g ae ha⁻¹ at 3 d after treatment, but symptoms declined to <10% by 4 wk after treatment (WAT). Chlorophyll fluorescence was not significantly affected at 2 and 4 WAT. Height reduction at 4 WAT occurred only at the highest dicamba rate (1,440 g ae ha⁻¹), but differences disappeared by maturity. Dry biomass reduction was also dose-dependent, reaching 16% for Cultivar A and 10% for Cultivar B at the highest rate. Pod reduction in DR soybean was minor (<3.5%) and not significant. Applications of dicamba from 288 to 864 g ae ha⁻¹ resulted in minimal yield reductions (<5%) and no significant biomass reduction. At a dicamba dose of 1,152 g ae ha⁻¹, yield reductions reached 7% and 9% for Cultivars A and B, respectively, while the highest rate (1,440 g ae ha⁻¹) resulted in yield reductions of 12% (Cultivar A) and 14% (Cultivar B). Despite over-the-top application restrictions, these results confirm that DR soybean cultivars tolerate rates (≤720 g ae ha⁻¹) of dicamba that were previously registered for postemergence weed control with minimal (<5%) yield reduction and recover rapidly from transient injury. However, applications above these rates can reduce yield by up to 14%, highlighting the importance of adhering to recommended dicamba use guidelines.

Termination of an existing failed corn stand before replanting is essential. Two studies were conducted in Stoneville and Verona, MS, from 2020 to 2021 to evaluate timing of corn or soybean replanting following different herbicide treatments applied to simulated failed stands of corn. Treatments included paraquat alone at 841 g ai ha−1, paraquat at 841 g ha−1 + metribuzin at 211 g ai ha−1, and clethodim at 51 g ai ha−1 + glyphosate at 1,121 g ae ha−1 applied at the V2 growth stage. Replant timings were 1 and 7 d after herbicide treatment (DAT). Pooled across replant timings, paraquat + metribuzin provided the greatest control 3 DAT compared with other treatments in both studies. At 14 and 21 DAT, clethodim + glyphosate controlled more corn than did paraquat + metribuzin and paraquat alone. Control of a simulated failed corn stand with paraquat alone never exceeded 50% at 3 to 21 DAT. Soybean yield in all plots receiving herbicide treatment targeting simulated failed corn stands were similar and ≥2,150 kg ha−1. When applied at the V2 corn growth stage, both clethodim + glyphosate and paraquat + metribuzin controlled a simulated failed stand of corn. This study demonstrated the importance of terminating failed stands of corn before replanting because of dramatic reductions in yield in the plots not treated with herbicide.

Glufosinate serves as both a primary herbicide option and a complement to glyphosate and other postemergence herbicides for managing herbicide-resistant weed species. Enhancing broadleaf weed control with glufosinate through effective mixtures may mitigate further herbicide resistance evolution in soybean and other glufosinate-resistant cropping systems. Two field experiments were conducted in 2020 and 2021 at four locations in Wisconsin (Arlington, Brooklyn, Janesville, and Lancaster) and one in Illinois (Macomb) to evaluate the effects of postemergence-applied glufosinate mixed with inhibitors of protoporphyrinogen oxidase (PPO) (flumiclorac-pentyl, fluthiacet-methyl, fomesafen, and lactofen; Group 14 herbicides), bentazon (a Group 6 herbicide), and 2,4-D (a Group 4 herbicide) on waterhemp control, soybean phytotoxicity, and yield. The experiments were established in a randomized, complete block design with four replications. The first experiment focused on soybean phytotoxicity 14 d after treatment (DAT) and yield in the absence of weed competition. All treatments received a preemergence herbicide, with postemergence herbicide applications occurring between the V3 and V6 soybean growth stages, depending on the site-year. The second experiment evaluated the effect of herbicide treatments on waterhemp control 14 DAT and on soybean yield. Lactofen, applied alone or with glufosinate, produced the greatest phytotoxicity to soybean at 14 DAT, but this injury did not translate into yield loss. Mixing glufosinate with 2,4-D, bentazon, and PPO-inhibitor herbicides did not increase waterhemp control, nor did it affect soybean yield compared to when glufosinate was applied alone, but it may be an effective practice to reduce selection pressure for glufosinate-resistant waterhemp.