There has been a renewed interest in the use of chlorimuron to control late-season Florida beggarweed in peanut. Postemergence (POST) applications of chlorimuron are one tool to help reduce economic losses from late-season Florida beggarweed populations. However, prior research has shown that peanut cultivar tolerance to chlorimuron varied among peanut cultivars and that applications of chlorimuron can increase the incidence of tomato spotted wilt virus (TSWV). Therefore, small-plot field trials were conducted from 2021-2024 near Ty Ty, Georgia to evaluate the response of seven peanut cultivars to POST applications of chlorimuron. Three separate experiments, each conducted three times, evaluated the response of AU-NPL17, FloRun 331, Georgia18RU, Georgia-20VHO, TifNV-High O/L Georgia-12Y and Georgia-16HO to chlorimuron applied POST. In each study, chlorimuron was applied at 9 g ai ha-1 with a non-ionic surfactant at 0.25% v/v to peanut at 65, 75, and 90 d after planting (DAP); a no chlorimuron treatment was included for comparison. Results indicated there was no interaction between chlorimuron timing and peanut cultivar. Application timing influence on peanut height and TSWV varied. When averaged over application timings, peanut height and TSWV incidence varied based on cultivar response ranging from 36 to 48 cm, and 9% to 38%, reduction compared with the non-treated, respectively. This is likely the result of natural variations in height and sensitivity to TSWV. Height reductions and increases in TSWV were observed depending on the experiment. However, regardless of height reductions and TSWV increases, peanut yield was reduced (8%) in experiment 2 (Georgia-12Y) when chlorimuron was applied 65 DAP and (13%) in experiment 3 (Georgia-16HO) when chlorimuron was applied at 75 DAP. These results suggest that these new cultivars express tolerance variability to POST applications of chlorimuron. Peanut growers should carefully consider cultivar selection for fields with problematic populations of Florida beggarweed if chlorimuron is to be used as a POST management strategy.

Blackgrass is a highly competitive weed in wheat fields and has increasingly evolved resistance to acetolactate synthase (ALS)-inhibiting herbicides. Ten field populations were screened, resulting in the selection of one highly resistant population (R-06) and one susceptible population (S-19) for detailed study. Whole-plant bioassays, ALS gene sequencing, molecular docking, metabolic inhibitor assays, glutathione S-transferase (GST) and ALS activity assays, and cross-resistance profiling were conducted to dissect the mechanisms of resistance. ALS sequencing identified three amino acid substitutions in R-06: Pro232Thr (P232T), His363Lys (H363K), and Trp574Leu (W574L). While W574L is a well-characterized ALS resistance-conferring mutation, P232T and H363K are outside major resistance hotspots and may serve secondary or compensatory roles. Molecular docking analyses predicted altered binding of mesosulfuron-methyl in the mutant ALS model, consistent with structural changes in the binding pocket. Metabolic inhibitor assays using malathion, piperonyl butoxide (PBO), and NBD-Cl resulted in modest increases in herbicide sensitivity, with a maximum reduction factor of 2.95 for PBO. GST activity was higher in R-06 at a single sampling time point (3 DAT). In addition, R-06 showed reduced sensitivity to several ALS inhibitors and reduced efficacy against selected herbicides with alternative modes of action. High-level resistance to mesosulfuron-methyl in the R-06 population is primarily associated with the ALS target-site mutation Trp574Leu, while the roles of Pro232Thr, His363Lys, and metabolism appear secondary and remain unresolved. These findings highlight complex resistance patterns in blackgrass and emphasize the need for diversified and integrated weed management strategies.

Alligatorweed, an invasive aquatic weed, has emerged as a major threat to sustainable crop production in various crop species. A two-year field study was conducted to investigate the impact of varied competition durations of alligatorweed on mungbean. The competition durations with alligatorweed included weed free conditions for first 3, 4, 5, 6 and 7 weeks after crop emergence along with a full season weed free treatment and alternatively weedy conditions for the aforementioned durations along with a full season weedy treatment. Competition with alligatorweed led to significant uptake of nitrogen (N), phosphorus (P) and potassium (K), with maximum uptake observed in the full season weedy treatment with N, P and K up to 65, 19, 56 kg ha-1, respectively. Additionally, significant accumulation of heavy metals (HMs) including copper (Cu), iron (Fe), manganese (Mn), zinc (Zn) and arsenic (As) up to 20, 16, 30, 14 and 11 g ha-1, respectively, was observed. Full season weedy plots produced more alligatorweed biomass and caused reductions of up to 81% in mungbean yield components. Alligatorweed infestation resulted in significant mungbean grain yield losses of up to 44% during 2022 and 52% in 2023, respectively. Furthermore, the three-parameter log-logistic equations identified the period from 4.2 to 6.8 weeks after crop emergence (WACE) as the critical period of alligatorweed competition that could result in a 10% yield loss in mungbean. Hence, alligatorweed poses a significant threat to mungbean production due to its strong competitive ability. However, its potential for HM accumulation offers promising opportunities for phytoremediation in both aquatic and terrestrial environments.

The increasing prevalence of herbicide-resistant weeds underscores the need to integrate non- chemical weed management approaches in soybean. Weed electrocution may be a viable option; however, limited research exists on the subject. A multi-state study was conducted to evaluate electrocution as a late-season weed control method in soybean across six Midwestern states, including Illinois, Indiana, Iowa, Kansas, Missouri, and Nebraska. The Weed Zapper™ electrocution implement was assessed across thirteen site-years during 2021 and 2022. The objectives of this study were to (i) evaluate the efficacy of weed electrocution on various weed species at travel speeds of 4.8 and 8.1 km h⁻¹, and (ii) compare the efficacy with other commercially available weed control options. Other non-chemical weed control treatments, which varied by location and were evaluated at selected site-years, included an inter-row cultivator, a tine cultivator, a row shaver, and a weed wiper. Weed species differed in their responses to electrocution, with the greatest control observed for giant ragweed (85%) at 14 d after treatment (DAT). Waterhemp control ranged from 43% to 78% across seven site-years, with ≥70% control achieved at four site-years. Averaged across weed species, control did not differ between electrocution speeds at 7 DAT, 14 DAT, or at soybean harvest. Weed electrocution generally provided similar or lesser control than other non-chemical treatments. In Illinois, waterhemp control with electrocution (78%) was comparable to single (65%) and sequential pass (88%) inter-row cultivation at 14 DAT in 2022. In Kansas, electrocution provided similar Palmer amaranth control (40%) to the row shaver in 2022, but lesser control in 2021 (50% vs. 73%). The results from this study suggest that weed electrocution could be a component of integrated weed management for late-season weed escapes in soybean.

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.

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.