Herbicide-resistant Palmer amaranth has been problematic within the United States for the past 30 years. The recent introduction of Palmer amaranth into the Pacific Northwest (PNW) prompted extensive surveys in 2023 and 2024 to collect seed samples for herbicide-resistance screening and leaf tissue for resistance-mechanism genotyping. Greenhouse dose-response bioassays were conducted in Kimberly, ID, during the summer of 2024 to assess the response of Palmer amaranth populations to selected postemergence herbicides. Resistance to glyphosate predominated across populations, and reduced sensitivity to 2,4-D, dicamba, and mesotrione was also observed. In contrast, glufosinate and saflufenacil provided effective control of PNW Palmer amaranth populations. Based on the dose-response bioassays, the effective dose required to provide 90% control (ED90) of the suspected glyphosate-resistant populations was 20 to 63-fold compared to the susceptible population. Subsequent 5-enolpyruvylshikimate-3-phosphate synthase (EPSPS) gene duplication analysis was conducted to confirm glyphosate resistance in the Palmer amaranth populations. About 74% (17 of 23) of the Palmer amaranth tissue samples showed gene duplication, with up to 150 copies of the EPSPS gene. The EPSPS gene amplification analysis of plants that survived 2X rate of glyphosate (2,520 g ae ha-1) showed up to 150 EPSPS genes in glyphosate-resistant populations. The widespread glyphosate resistance in the collected samples suggests that Palmer amaranth populations are being introduced into the PNW from locations where resistance to herbicide sites of action has previously evolved.

Cover crops have been progressively adopted by growers as a sustainable approach 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. The two-year 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 solo cereal rye 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 a cover crop mixture and cereal rye delayed the critical timing for weed removal (CTWR) by approximately 2 wk compared with winter fallow. The 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 cover crop mixture, cereal rye, and winter fallow was 1.4 wk, 0.1 wk, and 2.6 wk, respectively. In both years, single-species cereal rye resulted in the shortest CPWC due to its early-season weed suppression, while winter fallow resulted in 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 and provide greater yield protection to soybeans.

The impact of white-tailed deer browsing on crop yields, specifically soybean yield, has been a problem within agriculture for several decades. In an effort to reduce the losses incurred by deer browsing, several wildlife repellents have been commercialized and marketed for use on soybean. Despite their availability, limited research has been conducted on the ability of these repellents to deter feeding or the effects of these products on weed control when applied in combination with common herbicides. In 2023 and 2024, a field experiment was conducted in four soybean fields 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 the preplant burndown, early postemergence, and late postemergence pesticide applications, respectively. Regular assessments of deer browsing were conducted at weekly intervals following applications. Across all locations in 2023 and 2024, all applications of repellent products, even three sequential applications of these products, failed to provide any consistent suppression in deer browsing throughout the growing season. An additional field experiment was conducted during both seasons to evaluate the potential impacts of combinations of common herbicides and deer repellents on weed control 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 of post-emergent herbicides alone. Overall, the results from these experiments indicate that combinations of these deer repellent products with herbicides in tank mixtures do not increase or decrease weed control when compared to stand-alone herbicide treatments. There is also no evidence that these repellent products effectively deter deer browsing during the time frame when the soybean plant may be most vulnerable.

Cotton production in the Texas High Plains faces significant challenges due to water scarcity resulting from uneven rainfall patterns and declining levels of the Ogallala aquifer. Deficit or reduced irrigation is one of the most common water management strategies to increase water use efficiency and cotton productivity in the region. However, deficit irrigation can affect the efficacy of herbicides on weeds. This study investigates how varying irrigation levels affect herbicide efficacy on weeds in cotton production systems. A two-year field study was conducted at Texas Tech University Quaker Research Farm in 2023 and 2024. The experiment was randomized three times in a split-plot design with two irrigation levels: I1 [100% crop evapotranspiration (ETc) replacement] and I2 [50% ETc replacement] as the main plot factor and different pre-emergent (PRE) and post-emergent (POST) herbicide combinations as the subplot factor. Results indicated that reducing the irrigation level to I2 did not affect the total weed density or biomass production but resulted in decreased Palmer amaranth height and biomass production compared to I1. Among herbicide treatments, acetochlor, prometryn, or S-metolachlor PRE fb glyphosate + acetochlor, prometryn, or S-metolachlor POST provided the most effective weed control, reducing total weed density, Palmer amaranth weed density and biomass compared to the untreated control and to PRE alone. Although I2 resulted in lower plant height in both years than I1, it produced comparable cotton biomass and lint yield. Among the herbicide treatments, PRE fb glyphosate + residual herbicide POST yielded significantly higher lint yield than the untreated control in both years. In conclusion, the study demonstrates that deficit irrigation is an effective water conservation technique that maintains cotton yield and herbicide efficacy. Additionally, using PRE fb POST herbicide combinations, farmers can achieve effective weed control and sustain cotton productivity in semi-arid regions.

Herbicide resistance poses a significant challenge due to the increasing number of weeds resistant to multiple sites of action (SOAs). Recently, smooth pigweed populations resistant to glyphosate have been confirmed in the KwaZulu-Natal Province in the Republic of South Africa (RSA). This study evaluated herbicide products with different SOAs to provide alternative options for controlling glyphosate-resistant (GR) smooth pigweed populations. Dose-response assays for preemergence and postemergence herbicides were conducted under glasshouse conditions at the University of Pretoria, RSA. Seeds of GR smooth pigweed populations from Bergville and Winterton, and a glyphosate-susceptible (GS) population from Hendrina, were used. For the evaluation of preemergence herbicides (mesotrione, atrazine, imazethapyr, and acetochlor), seeds were sown in pots and herbicides were applied 12 hours after sowing. Postemergence herbicides (mesotrione, atrazine, tembotrione and atrazine tank mixture, and chlorimuron-ethyl) were tested on potted plants at the 6-leaf stage. Herbicides were applied at 0×, 0.5×, 1×, 2×, and 4×, where × is the recommended field rate for the herbicide products representing each SOA. Preemergence herbicides provided greater than 90% control across all populations. For postemergence herbicides, mesotrione effectively controlled all the GR populations, whereas the GS population from Hendrina exhibited reduced sensitivity (>50% survival). Atrazine was effective at rates higher than the recommended field rate in the GR populations. The tank mixture of tembotrione and atrazine had an additive effect compared to the sole application of mesotrione and atrazine. Chlorimuron-ethyl was only effective on the GS population. These results suggest that incorporating effective preemergence and postemergence herbicides into weed management programs could improve control of GR populations of smooth pigweed.

Despite its efficacy, little research has been conducted to evaluate the potential for electrocution to control common weeds in pastures. Electrocution could also potentially be utilized as a management tool to minimize the production of tall fescue seedheads to prevent fescue toxicosis in cattle. Separate experiments were conducted in Missouri in 2023 and 2024 to: 1) evaluate the effectiveness of electrocution on tall fescue seedhead management, and 2) evaluate forage injury and weed control following electrocution in comparison to common pre-packaged pasture herbicide combinations in mixed tall fescue and legume pastures. Sequential electrocution passes spaced 2 wk apart was the only electrocution treatment that resulted in reduced tall fescue seedhead density more than the nontreated control. However, metsulfuron-containing herbicide treatments reduced tall fescue seedhead density by 70 to 77%. In the weed control experiments, electrocution was compared to herbicide application in six mixed tall fescue and legume pastures and two johnsongrass-infested pastures in Missouri in 2023 and 2024. Most pre-packaged herbicide combinations tested eliminated white clover whereas electrocution and weed wiping had minimal effects on this species. The best electrocution treatments resulted in control of common ragweed, ironweed, common cocklebur, johnsongrass, and tall goldenrod and were comparable to that observed with the best herbicide treatments. Blackberry, sericea lespedeza and coralberry were most effectively controlled by weed wiping with glyphosate compared to all other treatments. Two passes of glyphosate with the weed wiper at 5 km/h spaced 2 wk apart providing the highest and most consistent control of johnsongrass. Results from these experiments indicate that electrocution can be used as a viable alternative to broadcast herbicide treatment for the control of several weeds that commonly occur in mixed tall fescue and legume pastures without significantly impacting forage yield or causing legume injury.

With the introduction of tetflupyrolimet as the first herbicide with a novel site of action in the last three decades, screening for herbicide resistance before commercialization has become integral to ensure successful applications. In the mid-southern United States, tetflupyrolimet is anticipated to be used as a preemergence (PRE) herbicide for barnyardgrass control but does exhibit postemergence (POST) herbicidal activity. In 2020, 45 Echinochloa crus-galli (barnyardgrass) accessions were collected from rice-producing areas in Arkansas and were screened in the greenhouse to tetflupyrolimet at 134 g ai ha-1 PRE and POST at the 2- to 3-leaf growth stage on a silt loam soil. A field experiment was conducted where tetflupyrolimet was applied alone at 134 g ai ha-1 or with clomazone at 336 g ai ha-1, to a susceptible barnyardgrass standard and four other accessions with confirmed resistance to florpyrauxifen-benzyl, imazethapyr, propanil, and quinclorac at the spiking, 1-, 2-, 3-, and 4-leaf stages. For the PRE screening, the percent visible control ranged from 88% to 99%, with some accessions differing in sensitivity to tetflupyrolimet. Percent mortality ranged from 47% to 90% at the PRE timing. Visible control and mortality ranged from 63% to 88% and 7% to 65%, respectively, from a POST application, suggesting there is differential sensitivity and that foliar applications may not be as effective as soil applications. In the field experiment, barnyardgrass accession did not influence POST biomass production and was impacted more by the growth stage at application, although the difference was frequently numerical. In general, applying tetflupyrolimet alone or with clomazone to ≥3 leaf grass compromised performance. Tetflupyrolimet will be better optimized as a soil-applied herbicide in mid-southern U.S. rice culture.

A seven-way herbicide-resistant Palmer amaranth accession (MSR2) was identified in AR. Herbicide programs providing season-long control of this problematic accession need to be investigated, especially within the current soybean portfolio. Therefore, this study aimed to evaluate the efficacy of different soybean herbicide programs for controlling seven-way-resistant Palmer amaranth accession, MSR2, emphasizing the contribution of residual herbicides to full-season suppression. Field experiments were conducted in 2022 and 2023 in Fayetteville, AR, in an area infested by MSR2. A total of 14 herbicide programs were tested, targeting available soybean technologies that enable glyphosate, glufosinate, dicamba, and 2,4-D. All herbicide programs had one or two postemergence herbicides applied at early postemergence (EPOST) and late postemergence (LPOST). Additionally, eight herbicide programs included residual herbicides at preemergence (PRE; S-metolachlor plus metribuzin) and EPOST (S-metolachlor). A nontreated control was included for comparison. Visible Palmer amaranth control (%) was assessed at LPOST and 2 weeks after LPOST (2 WA LPOST). Palmer amaranth plants were counted from two 0.25 m2 quadrats randomly marked at each evaluation, and the density reduction (%) was calculated compared to the nontreated control. Preplanned orthogonal contrasts were conducted to compare herbicide programs with or without residual herbicides. Overall, in both years, the highest MSR2 control at both evaluations was observed in the herbicide programs that included residuals at PRE and EPOST with postemergence treatments of 2,4-D or dicamba (single or mixed). For Palmer amaranth density, herbicide programs that relied on residuals at PRE and EPOST with sequential postemergence applications of 2,4-D plus glufosinate or dicamba plus glyphosate obtained higher reduction levels. Findings reveal that the addition of residual herbicides is crucial in controlling multiple-herbicide-resistant Palmer amaranth biotypes, like MSR2. Herbicide programs based solely on postemergence applications were ineffective in controlling accession MSR2.

Greenhouse studies were conducted to determine the response of stevia to several herbicide modes of action applied 2 wk after transplanting (WAP). At 1 wk after treatment (WAT), aciflourfen, metribuzin, and carfentrazone injured stevia 34 to 39%. In contrast, S-metolachlor, linuron, halosufluron, ethalfluralin, pyroxasulfone, pendimethalin, and tryfloxysulfuron injured stevia <20%, 1 WAT. By 4 WAT, stevia injury was ≤ 19% regardless of treatment, except metribuzin and trifloxysulfuron with 84 and 69% injury, respectively. S-metolachlor, linuron, ethalfluralin, pendimethalin, and pyroxasulfone did not reduce aboveground biomass compared to the nontreated check, 4 WAT. Linuron, ethalfluralin, pendimethalin, and pyroxasulfone did not reduce belowground biomass. Linuron, pendimethalin, and ethalfluralin may provide new modes of action for POST-transplant weed management in stevia. However, further research is needed to evaluate the effect of these herbicides on stevia growth and quality in the field.

New technologies in grain sorghum allow for the use of multiple acetyl CoA carboxylase- (ACCase) or acetolactate synthase- (ALS) inhibiting herbicides for johnsongrass control. With the growing issue of herbicide resistance, producers need to understand which herbicides will successfully control johnsongrass accessions. To determine the efficacy of herbicides recently registered or ones with potential to become available for use in grain sorghum, johnsongrass seeds were collected from 2017 to 2021 in Arkansas, Kansas, Texas, and Oklahoma and were screened for sensitivity to fluazifop, quizalofop, nicosulfuron, and imazamox. Additionally, glyphosate sensitivity was evaluated because of its use before planting or postharvest. Quizalofop resulted in 100% mortality of all johnsongrass accessions. Of the johnsongrass accessions evaluated, 89% were completely controlled with glyphosate. The ALS inhibitors nicosulfuron and imazamox resulted in 100% mortality of all Oklahoma accessions, but failures occurred on samples from other states. One accession from Kansas, 12 from Texas, and eight from Arkansas were found to have reduced sensitivity to nicosulfuron and imazamox. If producers plan to plant grain sorghum in areas with johnsongrass populations, an ACCase-inhibitor herbicide will most likely provide effective control. Imazamox and nicosulfuron, in conjunction with the appropriate trait, can be utilized in areas with sensitive johnsongrass populations or where other sensitive grass species are present.