Weeds are one of the greatest challenges to snap bean (Phaseolus vulgaris L.) production. Anecdotal observation posits certain species frequently escape the weed management system by the time of crop harvest, hereafter called residual weeds. The objectives of this work were to (1) quantify the residual weed community in snap bean grown for processing across the major growing regions in the United States and (2) investigate linkages between the density of residual weeds and their contributions to weed canopy cover. In surveys of 358 fields across the Northwest (NW), Midwest (MW), and Northeast (NE), residual weeds were observed in 95% of the fields. While a total of 109 species or species-groups were identified, one to three species dominated the residual weed community of individual fields in most cases. It was not uncommon to have >10 weeds m−2 with a weed canopy covering >5% of the field’s surface area. Some of the most abundant and problematic species or species-groups escaping control included amaranth species such as smooth pigweed (Amaranthus hybridus L.), Palmer amaranth (Amaranthus palmeri S. Watson), redroot pigweed (Amaranthus retroflexus L.), and waterhemp [Amaranthus tuberculatus (Moq.) Sauer]; common lambsquarters (Chenopodium album L.); large crabgrass [Digitaria sanguinalis (L.) Scop.]; and ivyleaf morningglory (Ipomoea hederacea Jacq.). Emerging threats include hophornbeam copperleaf (Acalypha ostryifolia Riddell) in the MW and sharppoint fluvellin [Kickxia elatine (L.) Dumort.] in the NW. Beyond crop losses due to weed interference, the weed canopy at harvest poses a risk to contaminating snap bean products with foreign material. Random forest modeling predicts the residual weed canopy is dominated by C. album, D. sanguinalis, carpetweed (Mollugo verticillata L.), I. hederacea, amaranth species, and A. ostryifolia. This is the first quantitative report on the weed community escaping control in U.S. snap bean production.

The commercialization of a three-way transgenic sugar beet cultivar, engineered for resistance to glyphosate, glufosinate, and dicamba (hereafter referred to as “triple-stacked”) is anticipated by the mid-2020s. While offering potential benefits for growers facing glyphosate resistance, two of three herbicides (dicamba and glyphosate) to be utilized with triple-stacked sugar beet (Beta vulgaris L.) have previously been used on major weeds in western U.S. cropping systems, raising concerns about preexisting resistance to these active ingredients. We conducted a field survey in sugar beet–growing counties of southeast Montana and northwest Wyoming in fall 2021, before the sugar beet harvest. We collected kochia [Bassia scoparia (L.) A.J. Scott], redroot pigweed (Amaranthus retroflexus L.), and common lambsquarters (Chenopodium album L.) populations and screened them for glyphosate, glufosinate, and dicamba resistance in greenhouse conditions. Our results showed two-way resistance (glyphosate and dicamba) in 32% of B. scoparia populations and reduced susceptibility to glyphosate in 78% of C. album populations. Additionally, we conducted a greenhouse experiment to assess the emergence patterns of collected populations. Phylogenetically closely related B. scoparia and C. album showed higher resemblance in emergence pattern than the distant relative A. retroflexus. While the majority of B. scoparia and C. album populations emerged in <20 d (time required to reach 90% emergence [E90] < 20 d], A. retroflexus populations required >30 d to reach E90. Widespread glyphosate and dicamba resistance in B. scoparia populations raises concerns about the long-term feasibility of a triple-stacked sugar beet cultivar. Furthermore, the delayed emergence of A. retroflexus may enable it to evade early-season weed management.

Echinochloa crus-galli var. crus-galli (L.) P. Beauv. (EC), Echinochloa crus-galli var. mitis (Pursh) Petermann (ECM), and Echinochloa glabrescens Munro ex Hook. f. (EG) are all serious rice (Oryza sativa L.) weeds that are usually treated as a single species in weed management practices. To determine interspecific and intraspecific differences in seed germination responding to different temperatures among the three Echinochloa weeds, we conducted field surveys and collected 66 EC, 141 ECM, and 120 EG populations from rice fields of East China in 2022; and tested their seed germination under 28/15 C (day/night), 30/20 C, and 35/25 C regimes, simulating temperatures of rice-planting periods for double-cropping early rice, single-cropping rice, and double-cropping late rice, respectively. In EC, ECM, and EG, seed percentage germination (cumulative percentage of germinated seed) and germination index (sum of the ratio of germinated seeds to the corresponding days) increased with increasing temperatures. At 28/15 C, the average percentage germination of EC populations (67.5%) was significantly (P < 0.05) higher compared with ECM (46.4%) and EG (43.7%); GD50 (duration for 50% total germination) for EC populations (5.2 d) was significantly shorter compared with ECM (5.9 d) and EG (5.8 d). At 35/25 C, the percentage germinations of EC (90.7%), ECM (80.5%), and EG (80.3%) were all significantly the highest among the three temperature treatments, respectively, and the GD50 values for EC (2.5 d), ECM (2.6 d), and EG (2.7 d) were all significantly the lowest. At 30/20 C and 35/25 C, the average germination percentages of populations collected from transplanted rice fields were significantly higher than those of populations collected from direct-seeded rice fields. Moreover, among EG populations, the longitudes and latitudes of collection locations were significantly correlated with seed percentage germination and germination indices. According to the interspecific differences and intraspecific variations of Echinochloa species, weed management strategies should also be customized according to the species and population characteristics in seed germination.

Two separate field experiments were conducted during the 2021 to 2022 and 2022 to 2023 growing seasons at Kansas State University Agricultural Research Center near Hays, KS, to understand the emergence dynamics of glyphosate-resistant (GR) kochia [Bassia scoparia (L.) A. J. Scott] as influenced by fall- and spring-planted cover crops (CC) and residual herbicide. Study sites were under winter wheat (Triticum aestivum L.)–sorghum [Sorghum bicolor (L.) Moench]–fallow rotation with a natural seedbank of GR B. scoparia. In Experiment 1, fall-planted CC mixture (triticale/winter peas/radish/canola) was planted after wheat harvest and terminated at triticale [×Triticosecale Wittm. ex A. Camus [Secale × Triticum] heading stage (next spring before sorghum planting). In Experiment 2, spring-planted CC mixture (oats/barley/spring peas) was planted in sorghum stubbles and terminated at oats (Avena sativa L.) heading stage. Four treatments were established in each experiment: (1) nontreated control (no CC and no herbicide), (2) chemical fallow (no CC but glyphosate + acetochlor/atrazine or flumioxazin/pyroxasulfone + dicamba were used to control weeds), (3) CC terminated with glyphosate, and (4) CC terminated with glyphosate plus residual herbicide (acetochlor/atrazine for fall-planted CC and flumioxazin/pyroxasulfone for spring-planted CC). Results indicated that fall-planted CC delayed GR B. scoparia emergence by 3 to 5 wk, whereas spring-planted CC delayed emergence by 0 to 2 wk compared with nontreated control. Fall-planted CC terminated with glyphosate plus acetochlor/atrazine reduced the cumulative emergence of GR B. scoparia by 90% to 95% compared with nontreated control across both years. Similarly, spring-planted CC terminated with glyphosate plus flumioxazin/pyroxasulfone reduced the cumulative emergence of GR B. scoparia by 83% to 90% compared with nontreated control. These results suggest that fall- or spring-planted CC in combination with residual herbicide at termination can be utilized for GR B. scoparia suppression. Results from this study will help in developing prediction models for GR B. scoparia emergence under different CC strategies.

Knotroot foxtail [Setaria parviflora (Poir.) Kerguélen], a perennial Setaria species, is becoming more problematic in forage and grazing systems across the southeastern United States. Setaria parviflora reproduces through the production of rhizomes and seeds, further complicating management strategies. Significant knowledge gaps exist regarding the biology and control of this species. This research aimed to understand the influence of burial depth on S. parviflora propagules and the physiological differences between it and other Setaria spp. Experiments were conducted between October 2019 and February 2021 in Clarke County, GA, to investigate the influence of burial depth (1, 2, 4, 8, and 16 cm) on the emergence and growth of S. parviflora rhizomes and seeds. Zero emergence was estimated at 8.7, 10.8, and 11.2 cm for small rhizomes, large rhizomes, and seeds, respectively. Therefore, producers could implement tillage events to a depth of 11.2 cm or greater to control S. parviflora. A separate study compared S. parviflora, yellow foxtail [Setaria pumila (Poir.) Roem. & Schult.], green foxtail [Setaria viridis (L.) P. Beauv.], and giant foxtail (Setaria faberi Herrm.) plant morphology. Despite similar aboveground appearances, S. pumila and S. parviflora had different total and belowground biomass 2 to 5 mo after emergence, which suggests differences in root formation and perennialization of S. parviflora. The present research determined that burying propagules using tillage could be included in management recommendations concerning S. parviflora; however, it should be complemented with herbicide applications during the growing season to assist in controlling S. parviflora plants produced by seeds.

Interseeding alfalfa (Medicago sativa L.) into corn (Zea mays L.) is a novel approach that increases the production of high-quality forage and reduces the risk of nutrient and soil loss from cropland. Annual grass weeds like yellow foxtail [Setaria pumila (Poir.) Roem. & Schult.] can reduce the success of alfalfa establishment and are difficult to manage in the interseeding system. This study evaluated ground cover, fall biomass, and fall plant density of interseeded alfalfa in response to varying populations of S. pumila. Our goal was to identify a threshold for initiating control of annual grasses to ensure good establishment of alfalfa in this intercropping system. Ground cover of interseeded alfalfa growing under corn declined as S. pumila density increased from 0 to 125 plants m−2 in July, August, and October with the sharpest decline in August (up to a 70% reduction in alfalfa cover). This reduction in ground cover was associated with a decline in postestablishment shoot and root mass and a reduction in alfalfa plant density from 246 to 146 plants m−2 in October. Results suggest that June S. pumila populations should be kept to less than 50 plants m−2 to obtain recommended fall alfalfa densities of 200 plants m−2 that are needed to maximize alfalfa yield the following year. This research provides crucial information to practitioners on when annual grass management is needed to ensure successful alfalfa establishment in this interseeded system.

Barley (Hordeum vulgare L.) and brown mustard [Brassica juncea (L.) Czern.] are winter cover crops known to produce allelochemicals that suppress plant growth. Incorporating barley or brown mustard residues into the soil before planting a spring-seeded cash crop may suppress early-season weeds in the cash crop; however, the comparative levels of weed suppression offered by barley and brown mustard cover crops incorporated into soil have not been determined. This study analyzed the relative capacities of barley and brown mustard cover crops to suppress early-season weeds of spring-seeded chile pepper (Capsicum annuum L.). Reductions in weed density or hand-hoeing time as a result of barley and/or brown mustard cover crop treatment were determined in two chile pepper fields in New Mexico over two growing seasons. For cover crop species that suppressed weeds in multiple site-years, a controlled environment study clarified possible growth stages adversely affected by determining the effects of cover crop–amended soil on the germination and seedling development of Palmer amaranth (Amaranthus palmeri S. Watson). Field study results indicated barley reduced early-season weed densities of chile pepper by up to 80% compared with the noncover control. Barley also reduced hoeing time in 3 of 4 site-years without affecting chile pepper fruit yield. Mustard cover crops reduced weed density in only 1 site-year (56% reduction relative to noncover control) and did not decrease hoeing time. The controlled environment study indicated that soil amended with barley slowed germination of A. palmeri without inhibiting seedling development. The results of this study indicate that a barley cover crop is more effective than brown mustard for early-season weed control of chile pepper in the southwestern United States.

Herbicide-resistant weeds threaten modern agriculture production. In Michigan, horseweed [Erigeron canadensis L.; syn.: Conyza canadensis (L.) Cronq.] is among the most troublesome weeds, and glyphosate was widely used to control E. canadensis. Due to extreme selection pressure imposed by heavy glyphosate usage, glyphosate-resistant E. canadensis is widespread. New technologies to control resistant E. canadensis are being introduced in the form of multiple herbicide resistance traits integrated into glyphosate-resistant soybean [Glycine max (L.) Merr.] (e.g., dicamba or 2,4-D choline). These new soybean varieties will likely increase the use of 2,4-D and dicamba, thus increasing the resistance selection pressure in E. canadensis. Predicting agronomic factors that drive herbicide-resistance evolution can serve as an effective proactive tool to advise practitioners to modify management strategies. Therefore, the objectives of this study are: (1) conduct dose–response assays to assess the current resistance spectrum of E. canadensis collected in Michigan and (2) predict and determine the main factors in row-crop production that contribute to resistance evolution in these accessions. Dose–response assays were conducted to evaluate the herbicide sensitivity spectrum to glyphosate, dicamba, and 2,4-D in 20 E. canadensis accessions collected from eight Michigan counties. Out of the 20 accessions, 60% were resistant to glyphosate, 35% to 2,4-D, and 20% to dicamba. Pearson’s correlation coefficient of dose–response values was positive in all comparisons (2,4-D-dicamba, r = 0.35; dicamba-glyphosate, r = 0.15; 2,4-D-glyphosate, r = 0.21). Dose–response data were integrated in odds ratio analyses to access the influence that previous management history had on the occurrence of resistance. Out of the significant pairwise comparisons, 44% were related to crop rotation frequency, 33% to previous herbicide-resistance status, and 22% to location where collected. Results highlight that growers have the ability to proactively manage herbicide-resistance evolution progression of E. canadensis in Michigan by adopting integrated weed management techniques to slow successive selection events that occur in low-diversity management systems.

False cleavers (Galium spurium L.) is an aggressive weed from the Rubiaceae. Here we assemble a chromosome-scale draft of its genome, laying the foundations for determining the genetic basis of auxinic herbicide resistance and for systematic research into its polyphyletic genus. We use the genome to examine the population genetics of material from the Canadian Prairies and, in concert with a common greenhouse experiment, to examine whether the phenotypic variation observed in the field results primarily from genetic or environmental factors. The genome assembly covers approximately 85% of G. spurium’s expected 360-Mbp genome size, with 94% of BUSCO (Benchmarking Universal Single-Copy Orthologs) genes complete and most single copy (89%). Approximately 37% of the genome is repetitive elements and 35,540 genes were annotated using RNA-seq data, including 100 homologues for genes involved in, or potentially involved in, herbicide resistance. The genome shows strong synteny with other members of the Rubiaceae, including smooth bedstraw (Cruciata laevipes Opiz) and robusta coffee [Coffea canephora (Pierre ex Froehner]. Double-digested RAD-seq data for the 19 populations from the Canadian Prairies indicated that G. spurium has high levels of population structure (FST = 0.54) and inbreeding (FIS = 0.86) with low levels of hetrozygosity (HO = 0.02) and nucleotide diversity (π = 0.0003). Variation in flowering time and seed weight largely overlapped among populations grown in the greenhouse. A redundancy analysis investigating genotype–phenotype associations showed few associations between single-nucleotide polymorphism (SNP) variation and these characteristics. In contrast, the majority of SNPs under selection were associated with mericarp hook density. This suggests that for most traits, environmental variation rather than genetic variation likely underlies phenotypic differences observed in the field. Several genes of interest, including several homologues involved in the assembly of the Skp1-Cullin-F-Box IR1/AFB E3 ubiquitin ligase complex (e.g., CAND1, ECR1), are located in areas of the genome with evidence of selection and are targets for further investigation.

Trifludimoxazin is a protoporphyrinogen oxidase (PPO)-inhibiting herbicide currently under development for preplant burndown and soil-residual weed control in soybean [Glycine max (L.) Merr.] and other crops. Greenhouse dose–response experiments with foliar applications of trifludimoxazin, fomesafen, and saflufenacil were conducted on susceptible and PPO inhibitor–resistant (PPO-R) waterhemp [Amaranthus tuberculatus (Moq.) Sauer] and Palmer amaranth (Amaranthus palmeri S. Watson) biotypes. These PPO-R biotypes contained the PPO2 target-site (TS) mutations ΔG210 (A. tuberculatus and A. palmeri), R128G (A. tuberculatus), and V361A (A. palmeri). The resistant/susceptible (R/S) ratios for fomesafen and saflufenacil ranged from 2.0 to 9.2 across all PPO-R biotypes. In contrast, the response of known PPO inhibitor–susceptible and PPO-R biotypes to trifludimoxazin did not differ within each Amaranthus species. In 2017 and 2018, experiments at the Meigs and Davis Purdue Agriculture Centers were conducted in fields with native A. tuberculatus populations composed of 3% and 30% PPO-R plants (ΔG210 mutation), respectively. At Meigs in 2018, A. tuberculatus control following foliar applications of fomesafen, lactofen, saflufenacil, and trifludimoxazin was greater than 95%. When averaged across the other 3 site-years, applications of 25 g ai ha−1 trifludimoxazin resulted in 95% control of A. tuberculatus at 28 DAA, while applications of fomesafen (343 g ai ha−1), lactofen (219 g ai ha−1), or saflufenacil (25.0 or 50 g ai ha−1), resulted in 80% to 88% control. Thus, at these relative application rates, the foliar efficacy of trifludimoxazin was comparable or greater on A. tuberculatus when compared with other commercial PPO inhibitors, even in populations where low frequencies of PPO-R plants exist. The lack of cross-resistance for common PPO2 TS mutations to trifludimoxazin and the level of foliar field efficacy observed on populations containing PPO-R individuals suggest that trifludimoxazin may be a valuable herbicide in an integrated approach for managing herbicide-resistant Amaranthus weeds.

Herbaceous perennials must annually rebuild the aboveground photosynthetic architecture from carbohydrates stored in crowns, rhizomes, and roots. Knowledge of carbohydrate utilization and storage can inform management decisions and improve control outcomes for invasive perennials. We monitored the nonstructural carbohydrates in a population of the hybrid Bohemian knotweed [Polygonum ×bohemicum (J. Chrtek & Chrtková) Zika & Jacobson [cuspidatum × sachalinense]; syn.: Fallopia ×bohemica (Chrtek and Chrtková) J.P. Bailey] and in Japanese knotweed [Polygonum cuspidatum Siebold & Zucc.; syn.: Fallopia japonica (Houtt.) Ronse Decr.]. Carbohydrate storage in crowns followed seasonal patterns typical of perennial herbaceous dicots corresponding to key phenological events. Starch was consistently the highest nonstructural carbohydrate present. Sucrose levels did not show a consistent inverse relationship with starch levels. Lateral distribution of starch in rhizomes and, more broadly, total nonstructural carbohydrates sampled before dormancy break showed higher levels in rhizomes compared with crowns. Total nonstructural carbohydrate levels in crowns reached seasonal lows at an estimated 22.6% of crown dry weight after accumulating 1,453.8 growing degree days (GDD) by the end of June, mainly due to depleted levels of stored starch, with the estimated minimum of 12.3% reached by 1,220.3 GDD accumulated by mid-June. Depletion corresponded to rapid development of vegetative canopy before entering the reproductive phase in August. Maximum starch accumulation in crowns followed complete senescence of aboveground tissues by mid- to late October. Removal of aboveground shoot biomass in late June to early July with removal of vegetation regrowth in early September before senescence would optimize the use of time and labor to deplete carbohydrate reserves. Additionally, foliar-applied systemic herbicide translocation to belowground tissue should be maximized with applications in late August through early fall to optimize downward translocation with assimilate movement to rebuild underground storage reserves. Fall applications should be made before loss of healthy leaf tissue, with the window for control typically ending by late September in Minnesota.

Barnyardgrass [Echinochloa crus-galli (L.) P. Beauv.] is a dominant weed species occurring in rice (Oryza sativa L.) fields across China. Metamifop, a common herbicide, is frequently applied to control E. crus-galli and other grassy weeds in rice fields. Herein, HS01, an E. crus-galli population suspected to be resistant (R) to metamifop, was collected from Hanshan County in Anhui Province, China. Whole-plant dose–response testing revealed that, compared with the susceptible (S) population FD03, HS01 had developed high-level resistance to metamifop with a resistance index (RI) of 11.76 and showed cross-resistance to cyhalofop-butyl (RI = 9.33), fenoxaprop-P-ethyl (RI = 5.80) and clethodim (RI = 3.24). Gene sequencing revealed a Cys-2088-Arg mutation in the ACCase 1,5 allele of all the R plants, while ACCase gene overexpression was not involved in the resistance. Molecular docking indicated that the less-negative binding energies might be the main reason for the resistance of HS01 to acetyl-CoA carboxylase (ACCase)-inhibiting herbicides. A derived cleaved amplified polymorphic sequence (dCAPS) method was developed for the rapid identification of the Cys-to-Arg mutation in the ACCase gene at codon position 2088 in E. crus-galli. Additionally, pretreatment with the cytochrome P450 inhibitor piperonyl butoxide or the glutathione S-transferase inhibitor 4-chloro-7-nitrobenzoxadiazole had no significant effects (P > 0.05) on the resistance of HS01 to metamifop. To our knowledge, this is the first report of a Cys-2088-Arg mutation in E. crus-galli ACCase that confers cross-resistance to ACCase-inhibiting herbicides.

Typically, weed density is used to predict weed-induced yield loss, as it is easy and quick to quantify, even though it does not account for weed size and time of emergence relative to the crop. Weed–crop leaf area relations, while more difficult to measure, inherently account for differences in plant size, representing weed–crop interference more accurately than weed density alone. Unmanned aerial systems (UASs) may allow for efficient quantification of weed and crop leaf cover over a large scale. It was hypothesized that UAS imagery could be used to predict maize (Zea mays L.) yield loss based on weed–crop leaf cover ratios. A yield loss model for maize was evaluated for accuracy using 15- and 30-m-altitude aerial red–green–blue and four-band multispectral imagery collected at four North Carolina locations. The model consistently over- and underpredicted yield loss when observed yield loss was less than and greater than 3,000 kg ha−1, respectively. Altitude and sensor type did not influence the accuracy of the prediction. A correction for the differences between predicted and observed yield loss was incorporated into the linear model to improve overall precision. The correction resulted in r2 increasing from 0.17 to 0.97 and a reduction in root mean-square error from 705 kg ha−1 to 219 kg ha−1. The results indicated that UAS images can be used to develop predictive models for weed-induced yield loss before canopy closure, making it possible for growers to plan production and financial decisions before the end of the growing season.

Efficient chemical weed management considers precise application of herbicides, maximizing herbicide retention and absorption, reducing the impact of abiotic factors, and mitigating off-target movement in order to optimize herbicide efficacy. Hence, this study assessed the employability and cost-efficiency of an unmanned aerial vehicle (UAV) for preplanting application and postemergence selective weed control of grasses infesting legume cover crops (LCCs) in an immature oil palm (Elaeis guineensis Jacq.) plantation. Field experiments were conducted in 2020 and 2021 at a research center and an oil palm replanting area in Jerantut, Pahang, Malaysia. Droplet deposition and distribution analyses revealed that the pressure at 0.25 MPa yielded better spray coverage and increased droplet counts compared with 0.15 MPa. For preplanting application, both the UAV and mist blower resulted in total weed control. Meanwhile for selective grass control in the LCCs, conventional knapsack sprayer (CKS) application provided slightly better weed control than the UAV over the 12-wk observation. However, a cost-efficiency analysis revealed that UAV spraying yielded economically favorable results for areas greater than 3,000 ha, with potential savings ranging from 4% to 28%. Furthermore, UAV spraying demonstrated superior operational efficiency and reduced working hours by 37%, water consumption by 91%, and human labor expenses by 81% compared with both conventional methods. These findings underscore the potential of UAV-based spraying for large-scale weed control in oil palm plantations and highlight its efficiency, comparable effectiveness, and cost-saving benefits.

Johnsongrass [Sorghum halepense (L.) Pers.], an invasive tallgrass, actively inhabits grassland ecosystems of North America. The grasslands ecoregions of the Southern Great Plains are particularly susceptible to S. halepense invasion and dominance because of its preferential growth in continental climate zones coupled with its ability to readily colonize recent disturbances associated with declining livestock grazing and anthropogenic energy and housing development. Controlling S. halepense via chemical or mechanical inputs can reduce this plant species’ abundance temporarily, but are typically followed by S. halepense reestablishment. Sorghum halepense does, however, provide high-quality forage and appears to withstand the frequent drought and flooding events associated with climate change in Southern Great Plains ecosystems. In this review, the benefits and drawbacks of S. halepense in Southern Great Plains grassland ecosystems are discussed and areas where research on this species could be expanded are identified.

Weed infestations have been identified as a major cause of yield reductions in canola (Brassica napus L.), a vital oil crop that has gained significant prominence in Iran, especially within Fars Province. Weed management using machine learning algorithms has become a crucial approach within the framework of precision agriculture for enhancing the efficacy and efficiency of weed control strategies. The evolution of habitat suitability models for weeds represents a significant advancement in agricultural technology, offering the capability to predict weed occurrence and proliferation accurately and reliably. This study focuses on the issue of dominant weed infestation in canola cultivation, particularly emphasizing the prevalence and impact of wild oat (Avena fatua L.) as the dominant weed species in canola farming in 2023. We collected data on 12 environmental variables related to topography, climate, and soil properties to develop habitat suitability models. Three machine learning techniques, including random forest (RF), support vector machine (SVM), and boosted regression tree (BRT), were estimated based on the receiver operating characteristic (ROC) and area under the curve (AUC) to model the distribution of A. fatua. Model performance was quantified using the ROC curve and AUC metrics to identify the best predictive algorithm. The findings indicated that RF, BRT, and SVM models exhibited accuracies of 99%, 97%, and 96% for the habitat suitability of A. fatua, respectively. The Boruta feature selection method identified the slope variable as significantly influential in A. fatua habitat suitability modeling, followed by plan curvature, clay, temperature, and silt. This study serves as a case study that highlights the utility of machine learning for habitat suitability predictions when information on multiple environmental variables is available. This approach supports effective weed management strategies, potentially enhancing canola productivity and mitigating the ecological impacts associated with weed infestation.

Weed management in California water-seeded rice (Oryza sativa L.) is challenging due to herbicide-resistant weeds. Research on additional herbicide options is necessary to control herbicide-resistant weeds. Pendimethalin is a dinitroaniline herbicide commonly used in dry-seeded rice; however, it is not registered in water-seeded rice. This study was conducted to determine the pendimethalin fate in water-seeded rice after application to 1-, 3-, and 5-leaf stage rice. Ultra-high performance liquid chromatography–tandem mass spectrometry (UPLC-MS/MS) was utilized to quantify pendimethalin and degradants in the water, soil, and rice seedling tissue at 1, 5, and 14 d after treatment (DAT). More than 50% of recovered pendimethalin was observed in the rice tissue and more than 25% in the soil, with the least amounts observed in the water at all application timings and sampling dates. Three pendimethalin degradants were observed at low concentrations: p36, [1-(1-ethylpropyl)-5,6-dimethyl-7-nitro-1H-benximidazole]; p44, [4-[(1-ethylpropyl) amino]-2-methyl-3,5-ditrobenzoic acid]; and p48 [4,5-dimethyl-3-nitro-N2-(pentan-3-yl) benzene-1,2-diamine]. Degradant p36 was observed in all samples and most abundant in the soil. Degradants p36 and p44 increased in concentration in the water by 14 DAT. Degradants p44 and p48 were at low concentrations or below the lowest level of quantification in water, soil, and tissue samples. The pendimethalin parent molecule remained intact and was not readily metabolized in rice tissue. The crown region and shoots of the rice seedlings demonstrated greater pendimethalin concentrations compared with the roots at all rice stages; however, pendimethalin concentrations remained similar across the three sample timings. Rice root and shoot reduction was 16% and 13%, respectively, after the 1-leaf stage application averaged over sample timings, and 6% and 4%, respectively, after the 5-leaf stage application. The results suggest the rice stage at the application timing is an important factor for pendimethalin tolerance; therefore, encouraging early root development can be beneficial for pendimethalin tolerance in water-seeded rice.

Accounting for 53% of U.S. peanuts (Arachis hypogaea L.), Georgia is the top peanut-producing state, with approximately 1.42 billion kg produced in 2023. Peanut producers often use the acetolactate synthase (ALS) imidazolinone herbicide imazapic, but reduced yellow nutsedge (Cyperus esculentus L.) control was reported in Georgia peanuts after 4 yr of continuous imazapic use. This study aimed to determine the level of resistance (LD50, I50, and GR50) and potential cross-resistance for the suspected resistant population and to identify the associated genetic mutations conferring resistance. A susceptible biotype was treated with 0, 0.0088, 0.0175, 0.035, 0.07, 0.14, 0.28, and 0.56 kg ai ha−1, and a resistant biotype was sprayed with 0, 0.07, 0.14, 0.28, 0.56, 1.13, 2.26, and 4.5 kg ai ha−1 of imazapic. To determine whether the suspected resistant biotype was cross-resistant to halosulfuron-methyl, an ALS herbicide used to control Cyperus spp., both biotypes were treated with 0, 0.0117, 0.0233, 0.0466, 0.0933, 0.187, 0.373, and 0.746 g ai ha−1 of halosulfuron-methyl. Plants were rated for injury at 7, 14, and 28 d after treatment (DAT), and aboveground biomass was harvested at 28 DAT. For imazapic, LD50 was 0.041 and 1.503 kg ai ha−1 and the GR50 was estimated to be 0.0128 and 1.853 kg ha−1 for Sus and Res biotypes, respectively, indicating 36- and 145-fold increase in resistance of the Res biotype for I50 and GR50, respectively. Both biotypes responded similarly to applications of halosulfuron-methyl, with biomass reduction at rates greater than 0.023 kg ai ha−1. Transcriptome profiles revealed a mutation in the target-site gene of the resistant biotype causing an amino acid substitution from alanine to valine at position 205 (Ala-205-Val). Growers should continue to rotate chemistries and implement integrated weed management approaches for control of C. esculentus, as the use of imazapic over consecutive years has led to resistance in C. esculentus.

Integrating cover crops (CCs) in dryland crop rotations could help in controlling herbicide-resistant weeds. Field experiments were conducted at Kansas State University Agricultural Research Center near Hays, KS, from 2020 to 2023 to determine the effect of fall-planted CCs on weed suppression in grain sorghum [Sorghum bicolor (L.) Moench], crop yield, and net returns in no-till dryland winter wheat (Triticum aestivum L.)–grain sorghum–fallow (W-S-F) rotation. The field site had a natural seedbank of glyphosate-resistant (GR) kochia [Bassia scoparia (L.) A. J. Scott] and Palmer amaranth (Amaranthus palmeri S. Watson). A CC mixture [winter triticale (×Triticosecale Wittm. ex A. Camus [Secale × Triticum])–winter peas (Pisum sativum L.)–canola (Brassica napus L.)–radish (Raphanus sativus L.)] was planted after wheat harvest and terminated at triticale heading stage before sorghum planting. Treatments included nontreated control, chemical fallow, CC terminated with glyphosate (GLY), and CC terminated with GLY+ acetochlor/atrazine (ACR/ATZ). Across 3 yr, CC terminated with GLY+ACR/ATZ reduced total weed density by 34% to 81% and total weed biomass by 45% to 73% compared with chemical fallow during the sorghum growing season. Average grain sorghum yield was 786 to 1,432 kg ha−1 and did not differ between chemical fallow and CC terminated with GLY+ACR/ATZ. However, net returns were lower with both CC treatments (−US$275 to US$66) in all 3 yr compared with chemical fallow (−US$111 to US$120). These results suggest that fallow replacement with fall-planted CCs in the W-S-F rotation can help suppress GR B. scoparia and A. palmeri in the subsequent grain sorghum. However, the cost of integrating CCs exceeded the benefits of improved weed control, and lower net returns were recorded in all 3 yr compared with chemical fallow.