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. This study evaluated herbicide products with different SOAs as alternative options for controlling glyphosate-resistant (GR) smooth pigweed populations. Dose-response assays for preemergence and postemergence herbicides were conducted under greenhouse conditions at the University of Pretoria, in South Africa. Seeds of GR smooth pigweed populations from Bergville and Winterton, and a glyphosate-susceptible (GS) population from Hendrina, were used. To evaluate preemergence herbicides (mesotrione, atrazine, imazethapyr, and acetochlor), seeds were sown in pots and herbicides were applied 12 h 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×of the field-use rate for the herbicide products representing each SOA. Preemergence herbicides provided >90% control across all populations. Among postemergence herbicides, mesotrione effectively controlled all the GR populations, whereas the GS population exhibited reduced sensitivity (>50% survival). Atrazine was effective when applied to the GR populations at rates higher than the recommended field-use rate. The tank mixture of tembotrione and atrazine had an additive effect compared to sole applications of mesotrione and atrazine. Chlorimuron-ethyl was effective only against 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.

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 2-yr 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 preemergent and postemergent 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 applied preemergence followed by glyphosate + acetochlor, prometryn, or S-metolachlor applied postemergence provided the most effective weed control, reducing total weed density, Palmer amaranth weed density, and biomass compared with the untreated control and to preemergence herbicides applied 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, a preemergence application followed by a postemergence application of glyphosate + residual herbicide 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 preemergence fb postemergence herbicide combinations, farmers can achieve effective weed control and sustain cotton productivity in semiarid regions.

Drill-seeded rice (DSR) offers several agronomic and environmental advantages over conventional puddled-transplanted rice (PTR), including labor and water savings, reduced cultivation costs, and lower greenhouse gas emissions. Despite these benefits, weed control remains a major bottleneck in the widespread adoption of DSR. Imidazolinone (IMI)-resistant rice, which allows the use of imidazolinone herbicides, has the potential to overcome weed control challenges in DSR and can therefore facilitate the transition from PTR to DSR. However, limited information exists on the effectiveness of IMI herbicide–based weed control programs in drill-seeded IMI-resistant rice in northwestern India. Field experiments were conducted in Karnal, India, from the 2020 through 2023 growing seasons to 1) evaluate the timing and rates of imidazolinone herbicides for effective weed control in IMI-resistant rice under DSR conditions, and 2) assess the potential carryover effects of IMI herbicides on succeeding crops. Results showed that sequential early postemergence applications of imazethapyr followed by (fb) late postemergence applications of either 100 fb 150 g ai ha−1 or 125 fb 125 g ai ha−1) effectively reduced the biomass of key weed species by 83% to 100%, including barnyardgrass, crowfootgrass, and Chinese sprangletop, and provided yields that were similar to weed-free treatments. These sequential postemergence treatments were consistently more effective than conventional preemergence herbicide applications of oxadiargyl fb a postemergence application of bispyribac-sodium. Sequential preemergence fb postemergence applications of imazethapyr were relatively less effective in controlling weeds and minimizing yield losses compared to sequential postemergence applications. However, in the second and third years, oxadiargyl (90 g ai ha−1) applied preemergence fb imazethapyr (100 g ai ha−1) applied postemergence achieved comparable weed control efficiency to those of sequential postemergence applications of imazethapyr (125 fb 125 g ai ha−1). No phytotoxicity was observed in the succeeding crops of wheat, mustard, chickpea, lentil, and corn from any of the herbicide treatments applied to IMI-resistant rice.

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.

Advancements in precision agriculture have driven the development of using drones to apply herbicides, offering the potential to address challenges associated with current application methods and improve weed management. This review synthesizes current research on spray drones to develop broad-use recommendations and identify challenges and knowledge gaps. Although spray drones cannot carry a heavy herbicide load compared with ground-based (high-volume backpack or tractor-mounted) sprayers, studies have reported comparable or superior weed control in addition to herbicide cost savings by using drones. However, spray drone performance is highly sensitive to operational parameters, because spray distribution and coverage/deposition are strongly affected by flight height and speed, carrier volume, nozzle design, crop growth stage, weed, and weather conditions. The bell-shaped curve of a single-pass spray pattern, which results in most spray deposition occurring directly under the drone, coupled with advances in imaging, remote sensing, and machine learning, demonstrate the strong potential of using drones for site-specific weed management purposes. Vegetation indices, multispectral imagery, canopy height models, and Light Detection And Ranging (LiDAR) technology have enabled crop-weed discrimination, though accuracy varies with species, growth stage, and image resolution. Deep-learning models such as You Only Look Once (YOLO), Residual Neural Network (ResNet), and Mask Region-based Convolutional Neural Network (Mask R-CNN) are good at weed detection, they remain limited by the quality of training data and their accuracy is reduced when they must detect small, overlapping, or dense weed populations. Spray drone–based offline mapping has enabled substantial herbicide savings by delineating weed patches, whereas real-time weed detection is constrained by onboard processing limits, battery life, and lower spatial resolution at operational flight heights. Ground-based smart sprayers offer higher real-time detection precision but they lack the field accessibility advantages of spray drones. Despite their potential, spray drones face challenges that include limited payload, off-target movement of herbicides, short battery life, regulatory challenges, and extensive license and complex software and calibration requirements. The downwind spray drift potential from drone applications is greater than ground applications but smaller than it is from piloted vehicles. An upwind swath offset is an ideal best management practice for reducing off-target herbicide movement to susceptible areas from both piloted and drone equipment. Future research should evaluate spray drones within integrated weed management systems, focusing on preemergence and foliar-applied contact herbicides, adjuvant use, and environmental and operational interactions to develop spray drone–specific guidelines and optimize spray performance.

Green kyllinga is a perennial sedge that forms dark green mats that can hinder production activities in specialty crop fields. Seeds of this species are highly viable, and seed dispersal can cause rapid increases in population density. In addition, new shoots are produced from each stem node of the underground rhizomes. Green kyllinga is primarily a weed of turf; however, it has increasingly been observed in the row middles (space between raised beds) in small fruit and vegetable crop fields in Florida. Trials were conducted to identify the most effective herbicide options from active ingredients registered for use in row middles. Lactofen (404 g ai ha−1) applied preemergence was the most effective at controlling green kyllinga emergence followed by pendimethalin (868 g ai ha−1). Glufosinate at rates of 189, 378, and 755 g ai ha−1 resulted in 75% to 93% control of vegetative green kyllinga shoots that were 1 cm tall. Glufosinate applied at rates of 378 and 755 g ai ha −1 delivered 96% and 100% control, respectively, on vegetative shoots that were 9 cm tall. Glufosinate was less effective on flowering green kyllinga, with >90% control achieved only at rates of 755 g ai ha−1. Shoot dry weight following glufosinate applications did not consistently decrease at the flowering stage until the highest glufosinate rate was applied. We conclude that preemergence applications of lactofen or pendimethalin followed by postemergence applications of glufosinate prior to flowering are effective management options for green kyllinga.

Weed seed buoyancy and survival in irrigation ponds were investigated as part of a larger study evaluating the potential for weed seed spread via overhead irrigation in container nurseries. Seed buoyancy was assessed for 13 weed species commonly found in container nurseries. Two of the 13 species were tested with the pappus intact or removed. Seeds were placed in water, and seed settling was recorded every 24 h for 168 h. Among the species tested, seed buoyancy ranged from 0% to 100%. Eclipta and marsh yellowcress maintained 100% and 99% buoyancy. In contrast, flexuous bittercress and yellow woodsorrel had 2% and 0% buoyancy. An attached pappus significantly increased seed buoyancy for both common groundsel and dogfennel. To test seed survival in irrigation ponds, seeds of spotted spurge, eclipta, flexuous bittercress, and yellow woodsorrel were placed in mesh bags and submerged at a depth of 60 cm in irrigation ponds at four nurseries. Seeds were collected from each location at 7, 15, 21, 30, 60, 90, 120, 240, and 360 d after submergence then germinated. All weed species germinated following 240 d of submergence. Flexuous bittercress and eclipta maintained greater than 80% germination following 360 d of submergence in three of four locations. In contrast, yellow woodsorrel seed germination was less than 15% following 240 d of submergence and less than 5% after 360 d in three of four locations. Spotted spurge seed germination declined over time but remained greater than 15% following 360 d of submergence. Results of these experiments show that seeds of several common nursery weeds are buoyant and remain viable while submerged for extended periods of time in irrigation ponds. Seeds that are both buoyant and survive in water may have greater potential for distribution by irrigation systems.

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 applied to silverleaf nightshade at three growth stages: 2 to 3 TL, 4 to 6 TL, and 7 to 10 TL (where TL represents the true-leaf stage). Seven preemergence herbicides were tested in a dose-response experiment at rates between 0.0625× and 2× of the recommended label rate on seedling emergence from three populations. Metribuzin, pyroxasulfone, pendimethalin, and sulfosulfuron suppressed seedling emergence by 80% to 90% at 28 d 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 (1×), and two exploratory rates, 0.5× and 2×. The biomass of the weed was reduced by more than 90% at all growth stages when aminopyralid and glufosinate were applied the 1× and 2× rates. Weed biomass was further reduced by 95% when fluroxypyr and imazapic at all application rates were applied to the weed at the 2- to 3-TL growth stage. At the 4 to 6 and 7 to 10 TL growth stages, biomass reduction >90% was achieved only at the 2× rate. Propane flaming at 33.3, 50, and 100 kg ha−1 and electrocution with 18, 45, and 90 J (which correspond to the 0.5×, 1×, and 2× application rates) were tested across the three growth stages. Both thermal methods were highly effective at the 2 to 3 TL stage by reducing biomass by >95%. The results highlight the importance of early intervention, because the efficacy of both herbicide and thermal treatments declined significantly as the weeds matured. Integrating preemergence and postemergence herbicides with thermal treatment could improve the long-term management of silverleaf nightshade in Mediterranean cropping systems.

Precision applications of herbicides are gaining interest as a sustainable approach to managing turfgrass pests. For instance, controlling turfgrass weeds with precision application could effectively reduce herbicide volume without sacrificing weed control. Machine learning models have been a common method for precision application, but machine learning requires intensive labor and expertise to collect and label imagery. The objective of this study was to develop and test a new system that uses the dark green color index (DGCI) to precisely apply glyphosate to detect and spray winter weeds in dormant bermudagrass turf. For this study, a sprayer prototype was constructed that used machine vision and DGCI. The prototype consisted of three primary components: 1) a camera that streamed video frames, 2) a control system that stored computer code focused on the integration of DGCI, and 3) solenoid valves that activated upon detection of winter weeds growing in dormant bermudagrass. Four field trials with different weed species and weed densities were established to test the DGCI system among traditional application methods (i.e., broadcast application and manual spot application with a backpack sprayer). In the lowest weed density scenario, the DGCI system accurately detected and sprayed 90% of the weed population, reducing herbicide volume by 62% compared to a broadcast application. Additionally, the DGCI system required less time for treatment than the spot application with a backpack sprayer. The results from these trials suggest that vegetative indices, such as DGCI, have potential in dormant bermudagrass systems to optimize herbicide volume.

This research was conducted in response to a report by a producer in southwestern Ontario of severe corn injury following an application that included multiple herbicides, an activator adjuvant, and a drift reduction agent. Eight field trials were conducted between 2024 and 2025 near Ridgetown, Ontario, Canada, to evaluate corn tolerance to mixtures of multiple active ingredients, an adjuvant, and drift retardent applied at two early postemergence growth stages (V2 to V3 and V3 to V4). Isoxaflutole applied alone or in combination with atrazine at either growth stage caused minimal visible corn injury at all time points, with ≤1% injury at 1 wk after application (WAA) and no injury at 2, 4, 6, and 8 WAA. Isoxaflutole + atrazine + glyphosate, applied at the V2–V3 or V3–V4 stage, caused 7% and 9% visible corn injury at 1 WAA and 3% and 5% at 2 WAA, respectively; however, visible corn injury was ≤1% at 4, 6, and 8 WAA. Isoxaflutole + atrazine + glyphosate + HiActivate, applied at the V2–V3 and V3–V4 stages, caused greater and more persistent visible corn injury, with 7% and 16% injury at 1 WAA and 5% and 10% injury at 2 WAA, respectively; visible corn injury declined to ≤5% at 4, 6, and 8 WAA. Isoxaflutole + atrazine + glyphosate + HiActivate + InterLock, applied at the V2–V3 and V3–V4 stages, caused 17% and 28% visible corn injury at 1 WAA and 11% and 17% at 2 WAA, respectively. Visible corn injury persisted with up to 8%, 7%, and 4% injury at 4, 6, and 8 WAA, respectively. There was no adverse effect on corn height, biomass, and grain yield with any of the treatments evaluated at either application timing. Results indicate that tank mixtures with multiple active ingredients can increase visible corn injury, but the injury was transient and did not affect yield.

Greenhouse studies were conducted to determine the response of stevia to several herbicide modes of action applied 2 wk after transplanting. At 1 wk after treatment (WAT), stevia was injured 34% to 39% by aciflourfen, metribuzin, and carfentrazone. In contrast, at 1 WAT, injury to stevia was <20% from S-metolachlor, linuron, halosulfuron, ethalfluralin, pyroxasulfone, pendimethalin, and trifloxysulfuron. 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 at 4 WAT. Belowground biomass was not reduced by ethalfluralin, linuron, pendimethalin, and pyroxasulfone. Linuron, ethalfluralin, and pendimethalin 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.

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.

Nursery crop producers in the southeastern United States use open ponds of captured water for irrigating container-grown plants, often without filtration. Many growers perceive irrigation water as a source of weed seed dispersal, but data on the presence of weed seeds in nursery irrigation ponds are lacking. The presence and diversity of viable weed seeds in irrigation pond water samples from six commercial container nurseries in central and eastern North Carolina were documented in the spring, summer, and late summer for two consecutive years. Irrigation pond water was filtered in 75,708-L increments using a custom-fabricated filtration system. The sample volume was chosen to approximate daily irrigation for 0.405 ha. A total of 216 filtrate samples were collected, six for each location, season, and year. Filtrates were spread on soilless substrate in plastic trays, and seedling emergence was recorded every 7 d for 12 wk. Irrigation samples from all locations, seasons, and years contained viable seeds. A total of 75 different taxa were present in the irrigation filtrates, including 28 weed species common to container nurseries. The average number of seeds collected at each location ranged from 9 to 35 per 75,708-L sample. Averaged across years and locations, there were 12.5, 24.8, and 18.2 germinable seeds per 75,708 L−1 in spring, summer, and late summer collections, respectively. Some common weed species such as eclipta, marsh yellowcress, large crabgrass, flexuous bittercress, and spotted spurge were present in samples from each season’s collections, whereas other species were unique to a single season. Although irrigation water introduced weed seeds, the number of weed seeds was small compared to other potential sources of weed seed dispersal within the nursery environment.

Fall panicum is a major annual grass weed in drill-seeded rice production systems on organic soils in Florida. Field studies conducted in 2021 and 2022 aimed 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 zero, 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 per square meter 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.

Branched broomrape was presumed to have been eradicated in California in the 1980s but has reemerged as a threat to the processing tomato industry. Although chemicals for suppressing branched broomrape have been used 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 laboratory-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, and 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 d) 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 observed only when fertilizers were applied during the germination stimulation stage. In the flooding studies, branched broomrape seed germination dropped to 20% after 14 d of flooding at 28 C. Flooding at both 10 C and 28 C reduced broomrape seed attachment to tomato plants by 50% within 7 d in the greenhouse study. These laboratory-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.

Managing yellow nutsedge and southern root-knot nematode (SRKN) is particularly challenging in organic sweetpotato production. Anaerobic soil disinfestation (ASD) has emerged as a promising nonchemical pest management strategy that entails incorporating labile carbon amendments into the soil, covering the soil with impermeable plastic mulch, and irrigating the amended soil to saturation. Field studies were conducted at Clemson University in Charleston, South Carolina, in the 2023 and 2024 growing seasons, to evaluate the effect of ASD on yellow nutsedge and SRKN. Treatments were structured as a factorial arrangement of three carbon amendments (Brassica residue [BR], chicken manure + molasses [CM+M], and cotton seed meal [CSM]) and an unamended control (UC) by four sweetpotato clones (Bayou Belle, Monaco, Murasaki-29, and USDA-18-040) with four replications using a randomized complete block design. ASD was terminated 3 wk after initiation, and sweetpotato slips were planted 1 wk after ASD termination. Greater cumulative anaerobicity was observed in the CM+M and CSM treatments with increments exceeding 220% relative to UC at ASD termination. Six weeks after planting, yellow nutsedge densities across all sweetpotato clones were significantly lower with CM+M (4 to 10 plants m−2) and CSM (6 to 8 plants m−2) treatments than the UC (21 to 27 plants m−2). Both bunch cultivars (Monaco and USDA-18-040) and spreading cultivars (Bayou Belle and Murasaki-29) sweetpotato clones resulted in similar yellow nutsedge densities. Soil population densities of SRKN at 16 wk after planting were reduced by 23% to 44% in CM+M treatments and by 29% to 46% in CSM treatments, relative to the UC. Marketable sweetpotato yield rose from 47% to 131% with the CMM and CSM treatments compared with UC yield. The findings of this study demonstrate that CM+M and CSM-induced ASD have the potential to suppress yellow nutsedge and SRKN in organic sweetpotato production systems while increasing the marketable sweetpotato yield.

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 (none, or one-pass two-pass postemergence 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% to 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.

Field trials were conducted in 2022 and 2023 in Lafayette, Indiana, to determine the response of a watermelon crop (cultivar Fascination) grown in plasticulture and weed control efficacy after pretransplant herbicide applications directed to the row middles, with or without a layby row middle application. Pretransplant herbicides included 1) ethalfluralin + clomazone, 2) fomesafen + S-metolachlor, 3) flumioxazin + S-metolachlor, and 4) flumioxazin + pyroxasulfone applied to row middles 1 d before the watermelon crop was transplanted. Each pretransplant treatment received one of three layby options: 1) no herbicide, 2) bicyclopyrone, or 3) imazosulfuron. A nontreated weedy control was included for comparison. At 2 wk after planting (WAP), the greatest weed control was provided by flumioxazin + S-metolachlor (95%), followed by flumioxazin + pyroxasulfone (92%), and ethalfluralin + clomazone (88%), but control was greater than when fomesafen + S-metolachlor (85%) was applied. By 8 WAP, weed control ranged from 69% (fomesafen + S-metolachlor) to 88% (flumioxazin + S-metolachlor). Flumioxazin + pyroxasulfone and ethalfluralin + clomazone provided 84% and 71% weed control, respectively. Weed control did not differ among layby herbicide treatments. Foliar crop injury was observed 1 wk after applying layby treatments of bicyclopyrone (7%) and imazosulfuron (2%), but it was minimal and not persistent. Relative to the nontreated weedy control, pretransplant herbicide treatments increased marketable yield by 59% to 68%, fruit number by 53% to 60%, and mean fruit weight by 4% to 10%. Pooled across all pretransplant 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.

Flumioxazin is a preemergence herbicide that is widely used pretransplant on conventional sweetpotato hectarage as part of weed management programs in North Carolina; despite this, some growers have concerns that flumioxazin may be injurious to sweetpotato, even at recommended rates if rain falls near application. Thus, field studies were conducted in 2021 and 2022 in Clinton, North Carolina, to evaluate the performance of flumioxazin under several simulated rain conditions. Studies evaluated a complete factorial arrangement of treatments with three flumioxazin rates and three simulated rain treatments. Herbicide treatments included no herbicide, and two rates of flumioxazin (107 g ai ha−1 and 214 g ai ha−1). Irrigation treatments included 1.9 cm of simulated rain applied before flumioxazin, 1.9 cm applied after flumioxazin, and no simulated rain. No visual injury from herbicide or rain treatments was observed. Yields of No. 1 and marketable sweetpotatoes were reduced by 25% and 14%, and total yield was reduced by 11% when the higher rate flumioxazin (214 g ha−1) was applied compared to the no-herbicide treatment. However, the lower (registered) rate of flumioxazin (107 g ha−1) did not lead to a reduction in yield compared with yield from the no-herbicide treatment. No interactions between irrigation timing and herbicide were observed, and irrigation timing alone did not affect sweetpotato yield. Average length-width ratio (LWR) was calculated for No. 1 sweetpotato storage roots as a metric of root shape. In 2021, herbicide did not affect LWR. In 2022, compared with the no-herbicide treatment, the LWR of No. 1 sweetpotato was smaller after the higher rate of flumioxazin (214 g ha−1) was applied compared with LHR of the no-herbicide treatment, resulting in rounder sweetpotato roots. Flumioxazin applied at 107 g ha−1 did not reduce LWR compared with the no-herbicide treatment. The results of this study highlight both the safety of flumioxazin when applied at registered rates and the importance of appropriate application procedures to prevent overapplication.

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. 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 signaling, suppresses jasmonic acid-mediated 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.