Purple nutsedge is a competitive and persistent perennial weed in the agronomic and horticultural cropping systems of the southeastern United States. Its management is a challenge during the growing season due to its ability to propagate vegetatively through underground rhizomes and tubers. Therefore, effective herbicide programs are needed that can check the spread of purple nutsedge and protect crop yields. Greenhouse experiments were conducted in 2024 to evaluate the response of purple nutsedge at two different growth stages (10 to 15 cm and 15 to 20 cm heights) to herbicides currently labeled for use in Mississippi cropping systems. Herbicides tested were glyphosate at 1,260 g ai ha–1, glufosinate at 672 g ai ha–1, bentazon at 1,680 g ai ha–1, halosulfuron at 69.5 g ai ha–1, and trifloxysulfuron at 6.9 g ai ha–1. Glyphosate was the most effective herbicide against purple nutsedge, providing >90% control, followed by halosulfuron, which provided 70% to 90% control at both growth stages. New shoot emergence was highest when glufosinate and bentazon were applied, and no new shoots emerged when glyphosate and halosulfuron were applied. More new shoots were observed when glufosinate and bentazon were applied when plants were 15 to 20 cm high compared to 10 to 15 cm. Shoot regrowth at 21 d after cutting the aboveground shoots indicated similar trends. A reduction of >90% in shoot and root biomass was observed when glyphosate, halosulfuron, and trifloxysulfuron were applied, whereas glufosinate and bentazon applications resulted in 50% less biomass reduction. Overall, herbicide efficacy against purple nutsedge was greater when plants were treated at the recommended height of 10 to 15 cm rather than 15 to 20 cm. The study results indicated that both herbicide mode of action and application timing are important for better purple nutsedge management in cropping systems.

Herbicide resistance poses an escalating challenge to successful weed management in contemporary cropping systems, prompting growing interest in integrated strategies to reduce reliance on herbicides. Although cover cropping has long been recognized for its potential to suppress weeds, it has recently gained renewed attention as a weed management tool and for its ability to help producers achieve broader goals of soil health and environmental sustainability. Although research on its efficacy in the midsouthern United States has accumulated, a meta-analytic synthesis has been lacking. This meta-analysis synthesized 746 effect sizes from 27 peer-reviewed studies (selected based on explicit reporting of weed suppression metrics, conducted in the midsouthern United States between 1991 and 2023) to assess cover crop weed suppression in the midsouthern region, which includes Alabama, Arkansas, Louisiana, Mississippi, eastern Oklahoma, Tennessee, and eastern Texas. Six key moderators and their two-way interactions were evaluated: tillage status of no-cover-crop controls, cover crop termination timing, weed control evaluation timing, cover crop type, weed functional group, and crop type, using a multivariate framework capturing study-level variation. The overall effect size was 36 (confidence interval [CI], 25–47], with most moderator levels showing positive effect sizes. Suppression was pronounced against no-till controls (mean difference [MD] = 43; CI, 30–55), while tilled controls exhibited moderated effects (MD = 27; CI, 14–39) due to the inherent weed suppression provided by tillage. Effects were greater for early evaluation timing (MD = 47; CI, 33–61) than late timing (MD = 34; CI, 20–48). Grass-legume mixtures provided the greatest suppression (MD = 70; CI, 56–84), while brassicas were ineffective (MD = 13; CI, 0–27). However, substantial two-way interactions among these moderators were prevalent, accompanied by high heterogeneity, indicating complex context specificity. Nonetheless, these findings highlight the weed suppression potential of cover crops and provide agroecologically informed quantitative insights into using cover crops for weed management in the region.

Italian ryegrass is a troublesome weed species commonly found across the United States. In North Carolina, biotypes resistant to herbicides from Groups 1, 2, and 9 have been confirmed. In fall 2020, multiple growers reported unsatisfactory control of Italian ryegrass after sequential burndown applications of paraquat in the Southern Piedmont region of the state. The objectives of this study were to confirm the presence of a paraquat-resistant Italian ryegrass biotype in the state through a whole-plant dose–response bioassay and to characterize the response of Italian ryegrass accessions from the same region to commonly used burndown herbicides. Greenhouse studies were conducted at the North Carolina State University weed science laboratories to evaluate the response of three putative paraquat-resistant Italian ryegrass biotypes (B, H, SB) and four putative susceptible biotypes (S1, S2, S3, and S4) to paraquat rates ranging from 52.5 to 26,880 g ai ha−1 and the response of 38 accessions to clethodim (271 g ai ha−1), glyphosate (1,260 g ae ha−1), glufosinate (880 g ai ha−1), nicosulfuron (34 g ai ha−1), and paraquat (840 g ai ha−1). The effective paraquat dose required to reduce biomass by 50% (GR50) for the putative paraquat-resistant biotypes ranged from 570 to 1,729 g ai ha−1, equivalent to 19- to 58-fold more resistant to paraquat compared to the average GR50 of susceptible biotypes. This study confirms the presence of paraquat-resistant Italian ryegrass in North Carolina. Results from the accessions study reveal that 29% of biotypes tested were resistant to paraquat, all of which also exhibited resistance to glyphosate and nicosulfuron. Additionally, a wide distribution of multiple herbicide–resistant biotypes was observed in the Southern Piedmont region, with 97% and 74% of accessions tested resistant to ≥1 and ≥2 sites of action, respectively.

A new formulation of pyroxasulfone + encapsulated saflufenacil has been developed. The encapsulated saflufenacil extends the application window to early postemergence. Pyroxasulfone, saflufenacil (suspension concentrate), and pyroxasulfone + encapsulated saflufenacil (microcapsule suspension) were applied to corn preemergence and evaluated for corn injury, corn yield, and visible weed control; in addition, the interaction (antagonistic, additive, or synergistic) was ascertained for each parameter. A total of six field trials were conducted over a two-year period (2022 and 2023) at three locations in southwestern Ontario. Pyroxasulfone was applied at 90, 120, and 150 g ai ha−1; saflufenacil was applied at 56, 75, and 95 g ai ha−1; and pyroxasulfone + encapsulated saflufenacil was applied at 146, 195, 245 g ai ha−1, equal to the combined rates of pyroxasulfone and saflufenacil. All pyroxasulfone, encapsulated saflufenacil, and pyroxasulfone + encapsulated saflufenacil treatments caused no corn injury. Weed control varied based on application rate and weed species. Reduced weed interference with pyroxasulfone + encapsulated saflufenacil at 195 and 245 g ai ha−1 resulted in corn yield that was similar to the weed-free control and the industry standard of S-metolachlor/atrazine/mesotrione/bicyclopyrone. The interaction between pyroxasulfone and encapsulated saflufenacil for weed control was additive.

Common milkweed is a creeping perennial weed that is problematic in row crops and pastures. Its ability to readily reproduce via adventitious root buds enables it to persist, and full control often requires several growing seasons of management. Although it is a troublesome agricultural weed, common milkweed is ecologically important due to its use as a food source for many arthropod species. Declines in common milkweed populations in North America have been correlated with and blamed for declines in monarch butterfly populations. This review summarizes available information on the biology, ecology, and management of common milkweed, as well as its potential uses and provisioning of ecosystem services.

The critical period for weed control (CPWC) has been used to define weed-control threshold triggers in many cropping systems. Using the CPWC to develop a weed-control threshold for broadleaf weeds that emerge later in the season would be valuable to cotton growers to enable them to schedule management of later emerging weeds to occur before crops suffer unacceptable yield losses. Field studies were conducted over two seasons from 2006 to 2008 to determine the CPWC for a broadleaf weed in cotton, using mungbean as a mimic weed. Mungbean was planted into cotton at densities of 1 to 50 plants m−2, at up to 450 growing-degree days (GDD) after crop planting, and removed at successive 200 GDD intervals after introduction, or left to compete full season. The data were fit to logistic and Gompertz curves. More complex models were developed and tested that included the time of planting and removal, weed density, height and biomass in the relationships. The CPWC models were able to predict the yield loss from later emerging weeds and together with an understanding of the expected growth rates of the weeds, the functions could be used predictively to determine the likely impact of delaying a weed-control input. This predictive element will be of value to cotton growers needing to coordinate weed-control inputs with other farm activities.

In-crop site-specific weed recognition systems have enabled precise and selective use of alternative nonchemical weed control technologies to provide much-needed support for weed management programs in large-scale cropping systems. Laser weeding has long been proposed, but only recently has it been commercialized as a highly precise, nonchemical weed control option for cropping systems. The weed control efficacy of several laser types (e.g., CO2, diode, fiber, and Nd:YAG) has been identified; however, no studies have investigated the use of readily available, high-power, low-cost consumer-grade laser diode arrays. The weed control efficacy of a 97-W, 445-nm laser diode array was investigated with the aims of evaluating 1) the irradiation energy requirement (as determined by treatment duration) of spot laser treatments required to control key grass (rigid ryegrass) and broadleaf (wild radish) weeds and 2) the influence of growth stage on energy requirement for annual ryegrass and wild radish control. Seedlings of rigid ryegrass and wild radish at growth stage 1 (GS1) were controlled by low laser energy densities of 0.2 to 0.5 J mm−2. As plant size increased, the energy densities required to control the seedlings increased substantially. For example, 2.0 J mm−2 was required to control GS4 rigid ryegrass, representing a 10-fold increase over that required for GS1 seedlings. Similarly aged but substantially larger wild radish seedlings remained mostly uncontrolled by 2.0 J mm−2 treatments. Wild radish was consistently more tolerant of laser treatments than annual ryegrass, but this difference was likely due to the more rapid growth rate that resulted in larger plants at the time of treatment, especially during warmer growing conditions. These results clearly define the potential for laser weeding using laser diode arrays and also identify the need for additional testing across a wider range of weed species with higher-powered, affordable diode arrays.

The history of weed science as a discipline has been a topic of interest for decades, but it is rare for researchers to consider publications prior to the 19th century or that were not focused on North America. In this article, the development of weed identification manuals in early modern England is documented out of two genres of premodern scientific writing: agricultural treatises and illustrated herbals. These two forms of writing intersected in the late 18th century with the publication of Thomas Martyn’s four-volume Flora rustica, an illustrated guide to plants in British agricultural systems. We argue that the key characteristics of modern North American weed identification guides in English (the use of the term weed to categorize plants, descriptions of plant habitats, and the use of detailed descriptions and/or illustrations of plants for identification purposes) originated in these premodern texts.

Native to North America, Virginia pepperweed is a winter annual weed in the mustard family (Brassicaceae) found commonly in agricultural crops, roadsides, landscapes, and other undisturbed areas. Known for its peppery taste, Virginia pepperweed has emerged as a troublesome and difficult-to-control weed in and around major row crops in the Mississippi Delta region. Recently, Virginia pepperweed management has become increasingly challenging due to the weed’s ability to survive control measures when applications are made beyond its early rosette stage and high fecundity rates (∼100,000 seeds plant−1). Therefore there is a need to develop effective control measures that could reduce the spread of Virginia pepperweed in crop production systems. Greenhouse experiments were conducted in the 2024 season to evaluate the activity of various burndown herbicides labeled for Virginia pepperweed control in row crops. Virginia pepperweed seed was stratified and germinated in a growth chamber, and seedlings were transplanted into pots and kept in a greenhouse. The herbicides tested at the 1X rate were glyphosate at 1,261 g ai ha−1, glufosinate at 672 g ae ha−1, 2,4-D at 1,065 g ai ha−1, and paraquat at 840 g ai ha−1. Herbicides were sprayed at three growth stages: early rosette, late rosette, and bolting. Virginia pepperweed control was evaluated at 1, 2, 3, and 4 wk after herbicide application (WAA). Shoot dry biomass data were collected at 4 WAA. Application of 2,4-D resulted in 95% to 100% Virginia pepperweed control at all three growth stages. Depending on the growth stage at which herbicides were applied, there was 40% to 50% control with glyphosate, 18% to 47% with glufosinate, and 0% to 71% with paraquat, with 0% biomass reduction at the bolting stage. However, the highest dry biomass reduction (>80%) was observed with 2,4-D applications at the early rosette stage. Herbicide applications at the early rosette stage resulted in maximum Virginia pepperweed control.

Certain plant species have the potential to establish themselves in agricultural fields, especially when they are already present nearby. Their spread can be influenced by improper management or intentional and unintentional introduction. Recently, cut-leaved gipsywort (Lycopus exaltatus L.) has been increasingly present in some row crops, where it was previously found only along field edges and irrigation channels, with no data about their presence in crops. Currently, no effective control methods for this rhizomatous species have been reported. To address this, 11 herbicides commonly used for weed management in major crops were evaluated in greenhouse studies. These included bentazon, dicamba, foramsulfuron, glyphosate, halauxifen-methyl, imazamox, mesotrione, nicosulfuron, tembotrione, thifensulfuron-methyl, and tribenuron-methyl. A dose-response study was conducted to identify the most effective option for cut-leaved gipsywort control using existing crop protection products. The study evaluated percentage reductions in dry biomass and canopy cover. The results suggest that bentazon, as the only nonsystemic herbicide, was least effective in controlling cut-leaved gipsywort with an effective dose (ED90) estimated at 1.5 × of the recommended labeled rate, or 2,205 g ai ha−1. Plants exposed to dicamba exhibited no regrowth at the field-use rate. Cut-leaved gipsywort may regrow when foramsulfuron, mesotrione, nicosulfuron, and tembotrione are applied at the recommended field-use rates. Halauxifen-methyl and imazamox were most effective, with estimated ED90 values of 0.21 × (0.85 g ai ha−1) and 0.4 × (16.14 g ai ha−1), respectively, which are lower than the recommended labeled rates. Although reduced rates are not recommended because good herbicide stewardship practices should aim to prevent the development of herbicide resistance, with both halauxifen-methyl and imazamox, cut-leaved gipsywort exhibited no regrowth when one-half of the recommended labeled rates were applied.

Tetflupyrolimet is a novel herbicide that inhibits dihydroorotate dehydrogenase in susceptible weeds, including those in warm-season turfgrass and rice. Given that warm-season species are managed alongside cool-season species that may be sensitive to tetflupyrolimet, research on its lateral movement within turfgrass is warranted. Field experiments were conducted in spring 2023 and 2024 at North Carolina State University to evaluate the potential downslope movement of tetflupyrolimet (400 g ai ha−1) compared with that of pronamide (1,160 g ai ha−¹), an herbicide that is known to move downslope. The studies took place on a 9.5% sloped plot of hybrid bermudagrass that had been established on Cecil sandy loam soil, under two moisture regimes at application: field capacity (≈34% volumetric water content) and saturation (≈46% volumetric water content). Before experimentation, the aboveground hybrid bermudagrass canopy was mechanically removed, and perennial ryegrass was planted as an indicator species. Herbicides were applied to treated areas (2.2 m2) upslope of data collection areas (8.6 m2), with subsequent irrigation and rainfall (2.5 cm total) 24 h after application. Downslope movement was assessed at 2, 4, 6, and 8 wk after treatment via perennial ryegrass mortality assessments made via grid (15 cm2) count. Downslope distances associated with a 50% probability of perennial ryegrass mortality (mortality50) were 1.2 to 3.6 times greater for pronamide compared to tetflupyrolimet. The maximum distance tetflupyrolimet moved was 1.1 m (regardless of soil moisture condition) each year. Comparatively, maximum downslope movement distances for pronamide were 1.5 to 1.65 m under saturated conditions and 1.5 to 1.8 m at field capacity. Overall, these findings suggest a 1.1-m buffer from sensitive species is likely sufficient to prevent undesirable injury following tetflupyrolimet applications to hybrid bermudagrass under conditions similar to this study.

The limited number of herbicides for use in peanut makes it difficult to diversify modes of action to combat advantageous weed species with reports of increasing herbicidal resistance. It is critically necessary to explore both new and repurposed chemistries with different modes of action for potential use on peanut crops. Little research has investigated peanut response to scenarios in which preemergence applications of fluridone or trifludimoxazin are delayed. Replicated field trials using small plots were conducted at the University of Georgia from 2022 to 2024 to identify any deleterious effects of fluridone applied at 126 g ai ha−1 or trifludimoxazin applied at 37 g ai ha−1 1, 3, 5, or 7 d after planting (DAP). The peanut population was not affected, regardless of herbicide or application timing. At 13 DAT, plant growth was reduced by 5% to 9% when fluridone had been applied 1, 3, 5, and 7 DAP. Visual crop growth was reduced by 10% to 19% with applications of trifludimoxazin, with the greatest effect occurring when it was applied at 7 DAP. Trifludimoxazin also caused 7% foliar leaf necrosis when averaged over application timings. Regardless of application timing, peanut height was reduced by both herbicides at 30 DAP but not at 80 DAP. However, at 80 DAP, plant width was reduced by 4% after fluridone and trifludimoxazin had been applied. Peanut yield was not affected by herbicide treatment regardless of when it was applied. Fluridone and trifludimoxazin applied as late as 7 DAP can injure peanut but not affect yield.

Greenhouse and field experiments were conducted in Kansas to test various postemergence herbicides for crop safety and weed control in pearl millet. Five pearl millet hybrids were used in greenhouse experiments and three hybrids (Hyb1, Hyb-2k, Hyb-3k) were used in field experiments at two sites. All herbicides were found to be safe (1% to 5% injury) for use on all pearl millet hybrids in both greenhouse and field experiments at 28 d after application (DAA), except imazamox and nicosulfuron, which were noted to cause 22% to 35% injury. At Site 1 at 42 DAA, 2,4-D, dicamba, bromoxynil + pyrasulfotole, 2,4-D + bromoxynil + fluroxypyr, and dicamba + 2,4-D effectively controlled Palmer amaranth by 88% to 91%, and density was reduced to 2 to 4 plants m−2 compared with 18 plants m−2 in nontreated control plots. The least control (60% to 65%) and greatest density (8 plants m−2) of Palmer amaranth was observed after applications of imazamox and nicosulfuron. In contrast, green foxtail was effectively controlled by 91% to 92%, and density was reduced to just 2 plants m−2 when imazamox and nicosulfuron were applied, whereas 13 plants m−2 were recorded in a nontreated control plot at 42 DAA. No weed emergence was observed at Site 2 regardless of treatment, including nontreated plots. High grain yields were recorded (Hyb1, 3,866 to 4,619 kg ha−1; Hyb-2k, 2,222 to 3,699 kg ha−1; and Hyb-3k, 822 to 1,315 kg ha−1) at both sites after applications of 2,4-D + bromoxynil + fluroxypyr. These results highlight that the postemergence herbicides tested in this study, except imazamox and nicosulfuron, can be safely used for weed control in fields of pearl millet.

Weeds pose a significant threat to Oregon field crops by reducing yields and compromising the quality of the harvested products. In fall 2024, Oregon stakeholders were surveyed to identify the key challenges and needs related to weed management in field crops. The survey consisted of eight questions, developed based on expert input and review of relevant literature, divided into three sections: respondent demographics, resource and support needs, and current weed management challenges and economic impacts. A total of 184 responses were collected statewide, with growers and crop consultants as the primary participants. Most respondents were from western Oregon, which may introduce a geographic bias to the findings. Respondents expressed particular interest in new herbicide technologies and herbicide resistance. Field days were the most preferred method for receiving weed management information. Annual bluegrass, Italian ryegrass, and roughstalk bluegrass were reported as the most problematic grass weeds, while wild carrot was the most problematic broadleaf weed. Most respondents reported an average weed control cost of US$125 to US$250 per hectare, and the majority indicated they were very concerned about herbicide resistance in their fields. The results from this survey will help guide future research and outreach efforts to improve weed management strategies in Oregon’s field crops.

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