Auxinic herbicides (Group 4) are a crucial tool for maintaining effective weed management in modern agronomic systems. Palmer amaranth has evolved resistance to multiple herbicides, including auxinic herbicides. With documentation of auxin resistance in Palmer amaranth, new strategies should be implemented to improve management. Field studies were conducted in Tennessee during the summers of 2024 and 2025 to evaluate the efficacy of different herbicide application methods for managing auxin-resistant Palmer amaranth. The research compared tank-mixed applications of 2,4-D and glufosinate with split-applied (split-boom; herbicides applied simultaneously through separate spray booms as independent solutions) applications across multiple Palmer amaranth populations. Results demonstrated that in populations exhibiting high auxinic resistance, the split-boom application method was more effective than the conventional tank-mix approach. However, control levels were still below those typically considered acceptable for effective Palmer amaranth contol. Sequential split-boom applications were required to achieve acceptable levels of control in these populations. A second study evaluated whether carrier volume influenced the performance of these applications by comparing mixtures of 140 L ha-1 and 280 L ha-1. The results indicated that carrier volume did not significantly affect Palmer amaranth control at these volumes.

Wild licorice is increasing in abundance across sandy grasslands of the Canadian Prairies, yet little is known about how to manage this plant. We conducted two field studies documenting the long-term impact of different herbicides applied one-time in either spring or summer, and annual mowing in either spring or summer, on the abundance of wild licorice for up to five growing seasons (2016-20). Herbicides led to variable reductions in licorice density and biomass between sites and over time, with the greatest reductions coinciding with summer rather than spring herbicides during the first two years post-treatment. Greater and more consistent decreases were evident from the application of aminopyralid and aminocyclopyrachlor, although all herbicides, including dicamba and 2,4-D, exhibited some suppression of licorice out to four years after treatment. Reductions in wild licorice also varied with growing conditions, as drought reduced licorice biomass across all treatments, including the non-treated control. Unlike herbicides, annual mowing, particularly in summer (late July; 9-10 leaf stage), increased wild licorice total annual biomass produced for up to two growing seasons, coincident with above-normal rainfall. With the onset of drought in year three, mowing effects dissipated and did not reappear through year five. Finally, while initially effective in reducing wild licorice, hand-pulling effects on licorice were short-lived, and the selective removal of neighboring herbs led to an increase in licorice during drought. Overall, these results highlight the challenge of managing wild licorice populations in grasslands and provide insight into the strategies that may aid the management of this species.

The prevalence of glyphosate- and ALS-inhibitor-resistant Palmer amaranth has substantially impacted sugar beet yield across CO and NE since 2020. While metamitron applied PRE has been previously reported to effectively control glyphosate-resistant (GR) Palmer amaranth, the rates evaluated in the literature are likely higher than what is practical for growers. Consequently, identifying an optimal rate will reduce potential herbicide use while still effectively controlling Palmer amaranth. Lower rates of metamitron may be sufficient to allow control of Palmer amaranth through the two true-leaf stage (2 TL) of growth, where very-long chain fatty acid (VLCFA) inhibiting herbicides can be used to layer additional residual herbicides and prevent Palmer amaranth emergence. Multiple dose-response analysis studies were established in Nebraska in 2020 and 2023, and in Colorado in 2023, to determine the necessary rate of metamitron, with and without a tank-mix partner of ethofumesate, to control Palmer amaranth through the 2 TL sugar beet stage. Metamitron rates ranged from 0 – 6.40 kg ai ha-1, while ethofumesate was included at a fixed rate of 1.68 and 1.86 kg ai ha-1 in 2020 and 2023, respectively. At all locations, maximum Palmer amaranth control was obtained near 4 kg ai ha-1 when applied alone. Adding ethofumesate as a tank-mix partner reduced metamitron use rate to about 2.9 kg ai ha-1. Trial results supported the issuance of a Section 18 label for metamitron at 3.27 kg ai ha-1 in Colorado and Nebraska in 2024, which subsequently extended to include Idaho, Wyoming, and Oregon in 2025.

Glufosinate is a key postemergence (POST) herbicide in U.S. soybean production, particularly where resistance to glyphosate and acetolactate synthase (ALS) inhibitors is widespread. A 25-question survey of soybean growers, agronomists, and industry professionals in Arkansas and Wisconsin was conducted in the Fall of 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% Arkansas; 88% Wisconsin), and suspected glufosinate resistance was reported by 37% of Arkansas respondents and 3% of Wisconsin respondents. Glufosinate was integrated into weed management programs by 84% of Arkansas respondents and 53% of Wisconsin respondents, and most applications targeted broadleaf weeds ≤15 cm tall. Carrier volume selections included 103–140 L ha−1 (75%; Arkansas) and 150–187 L ha−1 (86%; Wisconsin). Arkansas respondents most frequently reported using glufosinate in a sequential first and second POST program (62%). In Wisconsin, glufosinate use was most reported only in the first POST application (37%), followed closely by sequential use in the first and second POST 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% Arkansas; 67% Wisconsin), and spray water quality was rarely tested. Frequently reported tank-mix partners included glyphosate and PPO inhibitors 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 POST applications, lowering selection pressure and preserving glufosinate as an important POST option.

In plasticulture strawberry systems where growers intend to maintain plantings into a second harvest season, stolons (runners) are undesirable because they produce daughter plants that divert resources from the mother plant and complicate field maintenance. Manual runner removal is labor-intensive, and removal becomes more challenging once daughter plants have rooted in the row middles. Napropamide and pendimethalin were evaluated in greenhouse studies to assess their potential to suppress daughter-plant rooting and facilitate runner removal. Greenhouse studies used a threepot experimental unit consisting of one strawberry mother plant with two runners, each bearing one unrooted daughter plant, and two side pots simulating row middles. Three simulated herbicide application treatments were evaluated, including broadcast (foliar + side pot spray), in-row (foliar spray only), and row-middle (side pot spray only) applications, and were compared against a nontreated control. On mother plants, napropamide caused transient foliar injury but did not affect runner production or biomass. On daughter plants, napropamide caused transient injury and suppressed new growth at 4 wk after treatment (WAT), reducing daughter-plant biomass by 59–68%. Napropamide also eliminated the pull force required for removal relative to the nontreated control and reduced above- and belowground biomass up to 49% and by >95%, respectively, demonstrating effective suppression of runner establishment by reducing daughter plant rooting. However, suppression was transient; by 8 WAT, only the broadcast treatment consistently maintained rooting inhibition, likely due to herbicide degradation over time. Pendimethalin caused no effects on mother plants or daughter plants under any application method and failed to inhibit daughter plant rooting entirely. These results suggest that napropamide applied to the row middles, the only label-compliant method evaluated, can effectively suppress daughter plant rooting for at least one month, providing growers with a supplementary benefit of eased runner removal during summer weed management.

Non-chemical weed management is essential for advancing integrated weed management systems. Mid-infrared (MIR) radiation (3–50 µm) is a promising approach for heat-based thermal weed control with minimal fire risk. The lethal MIR energy requirement may be influenced by plant species, growth stage, and seed size. However, no published research has quantified the MIR energy dose (J cm-2) needed to control either weed seeds or various plant species at different growth stages. This study evaluated a dose range of 0–109 J cm-2 to identify minimum mid-infrared (MIR) energy thresholds required to control six species at the 3-, 6-, and 9-leaf growth stages, as well as dry and imbibed seeds of nine species. Responses were described using regression models based on dry biomass, survival, and reductions in viability. Overall responses varied across species, with smaller broadleaf weeds being most susceptible. Palmer amaranth was highly sensitive, requiring 13 and 56 J cm-2 to reduce biomass by 90% at the 3- and 6-leaf stages, respectively, while Italian ryegrass was highly tolerant, with 109 J cm-2 failing to achieve a 90% biomass reduction. Across all species, plants at the 9-leaf stage were highly tolerant, with no treatment achieving a 90% reduction. Dry Palmer amaranth seeds were the most tolerant, requiring 100 J cm-2 to reduce viability by 50%, compared with 8 J cm-2 for imbibed seeds. Conversely, dry barnyardgrass seeds were more susceptible, requiring just 16 J cm-2 for 50% viability reduction compared to 31 J cm-2 when imbibed. Seed size was moderately and positively correlated with the energy required for 50% viability reduction (r = 0.58). This study provides evidence that MIR radiation can serve as an effective thermal weed control tool, while also highlighting that efficacy varies among species, likely due to differences in morphology and physiology.

Fall panicum is a major annual grass weed in drill-seeded rice production systems on organic soils in Florida. Field studies were conducted in 2021 and 2022 to determine the effects of season-long fall panicum interference on rough rice yield on organic soils. The relationship between fall panicum density and percent rough rice yield loss relative to the weed-free control was described using the rectangular hyperbola model. Yield loss increased with increasing fall panicum density. The initial slope parameter (I), representing percent yield loss as density approaches 0, was estimated at 9.7%, indicating that even very low fall panicum densities caused measurable yield reductions. The asymptote parameter (A), representing percent yield loss as density approaches infinity, was estimated at 118%, suggesting that yield loss approaches 100% at very high fall panicum densities within the biological limits of the crop-weed interference. Within the observed density range (1 to 49 plants m-2), yield loss was predicted to increase from approximately 9% to 95%, and 50% yield loss was estimated to occur at 9 plants m-2. Thousand-grain weight declined linearly with increasing fall panicum density, with each additional fall panicum plant m-2 reducing thousand-grain weight by 0.18 g, indicating that fall panicum interference affected grain filling. These results demonstrate that fall panicum is highly competitive with rice and that even low infestations can result in substantial yield loss, showing the importance of timely and effective management in Florida rice organic soil production systems.

Reports of branched broomrape in California represent a reemerged threat to the processing tomato industry following its presumed eradication in the 1980s. Although chemical control programs for branched broomrape suppression have been developed in the past few years as an emergency response, limited research has been conducted on cultural practices that could be incorporated into integrated pest management programs. Three lab-scale studies were conducted in 2024 and 2025 to evaluate the responses of branched broomrape seeds to nitrogen fertilization and flooding. The fertilizer study evaluated the effects of diammonium hydrogen phosphate, calcium nitrate tetrahydrate, potassium chloride, potassium nitrate, ammonium nitrate, ammonium sulfate, and urea on branched broomrape seed germination and radicle elongation at various concentrations (0, 1.56, 3.125, 6.25, 12.5, 25, 50 mM) and at various seed germination stages (preconditioning, germination stimulation, and radicle elongation). The flooding studies evaluated the effects of flooding duration (3, 7, 14, 28, 42, and 56 days) and temperature (10 C and 28 C) on branched broomrape seed germination and the number of seed attachments to the tomato host plant. Results from the fertilizer study showed that fertilizers containing diammonium hydrogen phosphate, ammonium nitrate, and urea inhibited branched broomrape seed germination and radicle elongation, and this effect was only observed when fertilizers were applied during the germination stimulation stage. In the flooding studies, branched broomrape seed germination dropped to 20% after 14 days of flooding at 28 C. Flooding at both 10 C and 28 C reduced broomrape seed attachment to tomato plants by 50% within 7 days in the greenhouse study. These lab-scale data suggest that fertilization management and flooding have the potential to control branched broomrape infestation as cultural management strategies, but the results should be validated at the field scale in future experiments.

Field trials were conducted in 2022 and 2023 in Lafayette, Indiana, USA to determine plasticulture-grown ‘Fascination’ triploid watermelon response and weed control from pre-transplanting herbicide applications directed to the row middles, with or without a layby row middle application. Pre-transplanting herbicide applications included 1) ethalfluralin plus clomazone, 2) fomesafen plus S-metolachlor, 3) flumioxazin plus S-metolachlor, and 4) flumioxazin plus pyroxasulfone applied to row middles 1 day before transplanting. Each pre‑transplanting treatment received one of three layby options: 1) no herbicide, 2) bicyclopyrone, and 3) imazosulfuron. A non-treated weedy control was included for comparison. At 2 weeks after planting (WAP), the greatest weed control was provided by flumioxazin plus S-metolachlor (95%), which was similar to flumioxazin plus pyroxasulfone (92%) and ethalfluralin plus clomazone (88%), but greater than fomesafen plus S-metolachlor (85%). By 8 WAP, weed control ranged from 69% (fomesafen plus S-metolachlor) to 88% (flumioxazin plus S-metolachlor). Flumioxazin plus pyroxasulfone and ethalfluralin plus clomazone provided 84% and 71% weed control, respectively. Weed control did not differ among layby herbicide treatments. Foliar crop injury was observed 1 week after applying layby treatments with bicyclopyrone (7%) and imazosulfuron (2%), but it was minimal and not persistent. Relative to the non-treated weedy control, pre-transplanting herbicide treatments increased marketable yield (59 to 68%), fruit number (53 to 60%), and mean fruit weight (4 to 10%) similarly. Pooled across all pre-transplanting applications, a layby application of bicyclopyrone resulted in a greater relative increase in marketable fruit number and fruit weight than when no layby herbicide was applied.

Herbicide-resistant weeds remain a persistent challenge in soybean production across the southern United States, increasing interest in cultural practices that complement chemical control. Wheat–soybean relay intercropping (RIC) was evaluated relative to full-season soybean (FS) across three herbicide-use intensities (0-, 1-, or 2-pass POST programs) at two Arkansas sites (Fayetteville and near Colt) during the 2023 and 2024 soybean growing seasons. Weed control was assessed for Palmer amaranth and broadleaf signalgrass; weed biomass was quantified by grass and broadleaf groups, and seed production was measured for Palmer amaranth. Ground cover, cropping system yield, and economic outcomes were also evaluated. Compared with FS, RIC improved weed control most under reduced-input regimes (no herbicide or one-pass), maintaining a 6–16 % advantage even under the two-pass program. These gains corresponded to a 99% reduction in weed biomass and Palmer amaranth seed production relative to FS. RIC sustained nearly 90% ground cover during early and midseason intervals, limiting opportunities for weed seedbank recruitment and establishment. Across herbicide regimes, soybean-equivalent yield under RIC were comparable to or exceeded those of FS. Under low-input scenarios, profitability was greater under RIC because weed interference reduced FS performance; under the two-pass program, returns were similar between systems, indicating that RIC buffers economic performance when herbicide efficacy is uncertain. Break-even modeling across a wide range of crop prices further supported an economic advantage of RIC, with the largest gains under reduced-input herbicide programs. Collectively, these results indicate that RIC is operationally feasible and strengthens integrated weed management where herbicide performance is uncertain and resistance risk is elevated.

Early-season crop yield loss frequently occurs even when resources are abundant, challenging traditional resource-based models of crop–weed competition. Drawing on decades of research on the critical period for weed control, this review highlights evidence that brief exposure of crop seedlings to neighboring weeds can trigger rapid and irreversible reductions in yield potential through resource-independent mechanisms. Central to these processes are weed-induced changes in light spectral quality, particularly reduced red:far-red (R:FR) ratios, which activate the phytochrome-mediated shade avoidance syndrome (SAS). These responses alter morphology, biomass allocation, canopy architecture, photosynthetic capacity, redox homeostasis, defense signaling, and nitrogen metabolism. Low R:FR light induces persistent photosynthetic and metabolic constraints, increases reactive oxygen species (ROS) signaling, suppresses jasmonic acid- and salicylic acid-mediated defenses, and modifies nitrate assimilation and root traits in species- and genotype-dependent manners. Collectively, weed-derived signals during early crop development can lead to lasting physiological reprogramming. Integrating light-mediated signaling with metabolic, defense, epigenetic, and lncRNA-mediated pathways provides a mechanistic framework for understanding yield loss and identifies potential targets for enhancing crop competitiveness and resilience in weed-infested agroecosystems.

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.

Silverleaf nightshade, a highly invasive perennial weed, poses a serious threat to crops and orchards in Mediterranean regions. This weed reproduces both sexually, through seeds, and asexually, via an extensive rhizome network, contributing to its persistence and spread. Managing silverleaf nightshade is particularly challenging, requiring integrated chemical and non-chemical approaches. This study evaluated the effectiveness of preemergence and postemergence herbicides and thermal control methods at three growth stages (2-3, 4-6, and 7-10 true-leaf stages [TL]) of silverleaf nightshade. Seven preemergence herbicides were tested in a dose-response experiment at rates between 0.0625X and 2X of the recommended label rate on seedling emergence from three populations. Metribuzin, pyroxasulfone, pendimethalin, and sulfosulfuron suppressed seedling emergence by 80-90% at 28 days after treatment. Seven postemergence herbicides were tested on the same three seed populations, and on plants grown from rhizomes. Treatments were applied at three rates: the recommended label rate (1X) and two exploratory rates 0.5X and 2X. At the 1X and 2X rates, aminopyralid and glufosinate reduced biomass by more than 90% at all growth stages. Fluroxypyr and imazapic reduced biomass by more than 95% at the 2-3 TL growth stage across all application rates. At the 4-6 and 7-10 TL growth stages, biomass reduction >90% was achieved only at the 2X rate. Propane flaming at 33.3, 50 and 100 kg ha⁻¹ and electrocution with 18, 45 and 90 J (correspond to 0.5X, 1X and 2X application rates) tested across the three growth stages. Both thermal methods were highly effective at the 2-3 TL stage, reduced biomass >95%. The results highlight the importance of early intervention, as both herbicide and thermal treatments efficacy declined significantly as the weeds matured. Integrating pre and postemergence herbicides with thermal treatment could improve the long-term management of silverleaf nightshade in Mediterranean cropping systems.

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.

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.

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.