In small-plot experiments, weed scientists have traditionally estimated herbicide efficacy through visual assessments or manual counts with wooden frames—methods that are time-consuming, labor-intensive, and error-prone. This study introduces a novel mobile application (app) powered by convolutional neural networks (CNNs) to automate the evaluation of weed coverage in turfgrass. The mobile app automatically segments input images into 10 by 10 grid cells. A comparative analysis of EfficientNet, MobileNetV3, MobileOne, ResNet, ResNeXt, ShuffleNetV1, and ShuffleNetV2 was conducted to identify weed-infested grid cells and calculate weed coverage in bahiagrass (Paspalum notatum Flueggé), dormant bermudagrass [Cynodon dactylon (L.) Pers.], and perennial ryegrass (Lolium perenne L.). Results showed that EfficientNet and MobileOne outperformed other models in detecting weeds growing in bahiagrass, achieving an F1 score of 0.988. For dormant bermudagrass, ResNet performed best, with an F1 score of 0.996. Additionally, app-based coverage estimates (11%) were highly consistent with manual assessments (11%), showing no significant difference (P = 0.3560). Similarly, ResNeXt achieved the highest F1 score of 0.996 for detecting weeds growing in perennial ryegrass, with app-based and manual coverage estimates also closely aligned at 10% (P = 0.1340). High F1 scores across all turfgrass types demonstrate the models’ ability to accurately replicate manual assessments, which is essential for herbicide efficacy trials requiring precise weed coverage data. Moreover, the time for weed assessment was compared, revealing that manual counting with 10 by 10 wooden frames took an average of 39.25, 37.25, and 42.25 s per instance for bahiagrass, dormant bermudagrass, and perennial ryegrass, respectively, whereas the app-based approach reduced the assessment times to 8.23, 7.75, and 14.96 s, respectively. These results highlight the potential of deep learning–based mobile tools for fast, accurate, scalable weed coverage assessments, enabling efficient herbicide trials and offering labor and cost savings for researchers and turfgrass managers.

Weeds significantly reduce sugarcane (Saccharum officinarum L.) production by 30% to 50% and cause complete crop loss in severe cases. Guangxi, a central sugarcane-growing region in southern China, faces significant challenges due to the proliferation of weeds severely impacting crop tillering, yield, and quality. In this study, we surveyed and identified 35 weed species belonging to 16 families in Longzhou, Nongqin, and Qufeng, with significant threats posed by purple nutsedge (Cyperus rotundus L.), bermudagrass [Cynodon dactylon (L.) Pers.], hairy crabgrass [Digitaria sanguinalis (L.) Scop.], black nightshade (Solanum nigrum L.), white-edge morningglory [Ipomoea nil (L.) Roth], and ivy woodrose [Merremia hederacea (Burm. f.) Hallier f.]. The application of 81% MCPA-ametryn-diuron achieved greater than 90% control within 15 d. Although herbicides are effective, they can unintentionally harm sugarcane, indicating a need for tolerant genotypes. Therefore, we comprehensively evaluated herbicide-induced phytotoxic responses and identified tolerant sugarcane genotypes over 3 yr of trials conducted on 222 genotypes across Guangxi. We quantified phytotoxicity by counting the number and severity of affected leaves. The ANOVA revealed statistically significant main and interaction effects among genotype, crop cycle, and location. Cluster and discriminant analyses classified the genotypes into five groups: 21 highly tolerant (HT), 68 tolerant, 75 moderately tolerant, 18 susceptible, and 40 highly susceptible. The 21 HT genotypes demonstrated strong potential to be used as parental lines for breeding herbicide-tolerant varieties, to inform precision breeding strategies, and to increase tolerance to herbicide stress in sugarcane.

The presence of glufosinate-resistant Palmer amaranth (Amaranthus palmeri S. Watson) is of concern for Arkansas farmers. The objective of this study was to understand the distribution of glufosinate resistance among A. palmeri accessions collected in 2023 from locations surrounding MSR2 (a highly glufosinate-resistant accession) in 2020, focusing on the distance and direction patterns. Additionally, the cytosolic (GS1) and chloroplastic (GS2) glutamine synthetase copy number were quantified in glufosinate survivors. In 2023, a total of 66 A. palmeri samples were collected within a 15-km radius of MSR2. Amaranthus palmeri seedlings were treated with glufosinate at 590 g ai ha−1. Plant tissues were collected, and gene copy number assays were conducted with survivors from accessions showing less than 96% mortality. Glufosinate provided ≥80% mortality in most of the accessions evaluated. Nonetheless, a few accessions showed low mortality rates, with values as low as 34%. Within and among accessions, there was no variation for GS1.1 and GS1.2, while the GS2.1 and GS2.2 copy numbers varied greatly. There was no evidence that the geographic distance between samples and MSR2 impacted mortality or gene copy number. However, there was strong evidence that direction, relative to MSR2, affected both mortality and GS2.1 copies. Samples collected north from MSR2 showed lower average mortality rates (83%) with a higher number of GS2.1 copies (2.3). For comparison, average mortality ranged from 90% to 95% and GS2.1 copy number ranged from 1 to 1.2 in the other directions. The predominant summer and fall wind directions do not explain the movement of resistance in a specific direction. These findings indicate that there are multiple A. palmeri accessions capable of surviving a label recommended use rate of glufosinate in northeast Arkansas, and resistance distribution needs to be further investigated.

Horseweed [Erigeron canadensis L.; syn.: Conyza canadensis (L.) Cronquist (2n = 18), family: Asteraceae] is known as one of the 10 most troublesome and most commonly occurring weeds in 12 categories of broadleaf crops, fruits, and vegetables and is present in 2,540 counties across the United States. Wide phenotypic plasticity coupled with highly adaptive traits and reported allelopathy might have resulted in its rapid spread and extensive presence across the United States, presumably by altering the composition of local plant community. This study for the first time revealed the allelopathic effect of E. canadensis leaf aqueous extract (10%) on seed germination and seedling growth of seven common weeds, namely, Palmer amaranth (Amaranthus palmeri S. Watson), smooth pigweed (Amaranthus hybridus L.), prickly sida (Sida spinosa L.), and pitted morningglory (Ipomoea lacunosa L.), which are native to North America, and non-native lambsquarters (Chenopodium album L.), curly dock (Rumex crispus L.), and barnyardgrass [Echinochloa crus-galli (L.) P. Beauv.]. Erigeron canadensis aqueous extract significantly (P < 0.05) reduced the seed germination and seedling growth of A. hybridus, A. palmeri, R. crispus, and S. spinosa, but showed nonsignificant impacts on I. lacunosa, C. album, and E. crus-galli. Based on synthetical allelopathic effects (SE < 0), the order of inhibition from highest to lowest was as follows: A. hybridus (−0.580), R. crispus (−0.464), A. palmeri (−0.409), S. spinosa (−0.248), C. album (−0.143), I. lacunosa (−0.035), and E. crus-galli (0.009). Liquid chromatography of the E. canadensis aqueous extract identified a total of 38 compounds with previously known allelopathy, including piperidine, choline, 4-hydroxybenzaldehyde, acetonecyanohydrin, gallic acid, 2-furoic acid, genistein, and gentisic acid. The current study, utilizing a petri dish bioassay, explains E. canadensis’s invasive potential and mechanisms for affecting the succession of commonly occurring native and non-native weed species in the southern United States. These results establish a solid foundation for understanding the mechanisms driving the successful invasion of E. canadensis in its native range and provide a valuable theoretical framework for early-warning systems assessing ecological risks.

Redroot pigweed (Amaranthus retroflexus L.) is among the most troublesome weeds in the Intermountain West affecting corn (Zea mays L.) production and contributing to significant yield losses, in addition to losses caused by water stress. Improvements in agricultural technology such as use of drought-tolerant (DT) corn hybrids has helped minimize the impact of water stress on corn yields. However, it is not known how the use of hybrids affects the interactions between weeds and corn. This work evaluated the competitive effects of A. retroflexus on DT and drought-susceptible (DS) corn hybrids exposed to optimal and reduced irrigation levels in a semi-controlled study. The semi-controlled environment was established in a rainout shelter with corn maintained at a density of 66,482 plants ha−1 and A. retroflexus varied at densities of 0, 33,241, and 66,482 plants ha−1 that were then provided either optimal or reduced irrigation (100% and 50%). We observed a 45% reduction in the shoot biomass of DS corn under reduced irrigation, while the shoot biomass of DT corn remained the same under both irrigation levels in Season 1. In Season 2, both hybrids experienced a decrease in shoot biomass under reduced irrigation. Amaranthus retroflexus exhibited an 80% increase in shoot biomass when growing with DS corn exposed to reduced irrigation, compared with its growth with DS corn exposed to optimal irrigation. Conversely, DT corn negatively impacted A. retroflexus shoot biomass under reduced irrigation, resulting in only a 9% difference between the reduced and optimally irrigated plots. These findings suggest that DT corn may mitigate water stress while also providing the additional benefit of improved competition against weeds, effectively suppressing their growth in water-stressed environments.

Widespread resistance to selective postemergence herbicides has led to increased use of preemergence herbicides to control rigid ryegrass (Lolium rigidum Gaudin), the major weed of southern Australian cropping systems. Seeds of L. rigidum are dormant at maturity, leading to staggered germination across the growing season and avoidance of pre-sowing knockdown herbicides by the later-germinating cohorts. Although it is well known that this selects for higher seed dormancy in intensively cropped areas, there is less information on whether dormant seeds respond differently to preemergence herbicides applied at sowing. To address this, seeds of field-collected L. rigidum populations were divided into dormant and nondormant (afterripened) subsamples and treated with sublethal rates of three preemergence herbicides in order to monitor seedling emergence and seed persistence over 6 mo. The presence of prosulfocarb and pyroxasulfone eliminated the nearly 4-fold increase in seedling emergence that typically results from afterripening, while trifluralin was partially inhibitory. In all treatments, the proportion of viable seeds remaining in the soil after 6 mo was negligible (≤3% of the viable seeds originally sown) for both the dormant and nondormant seeds. Application of radiolabeled herbicides to soil and seeds showed that the herbicides persisted in the seed tissue for longer than in the bulk soil. Therefore, the presence of dormant L. rigidum seeds in the soil seedbank is unlikely to result in cohorts that can avoid preemergence herbicides.

Italian ryegrass [Lolium perenne L. ssp. multiflorum (Lam.) Husnot] is a significant weed in winter wheat (Triticum aestivum L.), corn (Zea mays L.), soybean [Glycine max (L.) Merr.], and peanut (Arachis hypogaea L.) crops in Alabama. In response to reports of herbicide failure, field surveys were conducted in these cropping systems across Alabama in 2023. The objectives were to document the distribution of herbicide resistance in the collected L. perenne ssp. multiflorum populations. Populations were evaluated in a greenhouse for sensitivity to herbicides representing three modes of action: an acetolactate synthase (ALS) inhibitor (pyroxsulam), two acetyl-coenzyme A carboxylase (ACCase) inhibitors (fluazifop-butyl and clethodim), and a 5-enolpyruvylshikimate-3-phosphate synthase (EPSPS) inhibitor (glyphosate). Herbicide screenings were followed by dose–response assays of the most resistant L. perenne ssp. multiflorum population for each herbicide at eight rates (0.5, 1, 2, 4, 8, 16, 32, and 64×) compared with a susceptible population at six rates (0.0625, 0.125, 0.25, 0.5, 1, and 2×). Out of 44 populations evaluated, 21%, 11%, 25%, and 2% were found resistant to glyphosate, fluazifop-butyl, pyroxsulam, and clethodim, respectively. Resistance levels were confirmed to be 192-, 14-, 90-, and 738-fold for glyphosate, fluazifop-butyl, pyroxsulam, and clethodim, respectively. Mutation detection studies revealed specific mutations: Asp-2078-Gly in the ACCase gene, Pro-106-Ser in the EPSPS gene, and a novel Arg-421-Thr mutation in the ALS gene.

This article aims to further our understanding of the mechanics of physical weed control, specifically the mechanism of using a cutting blade to cut weeds. Research on weed stem cutting is sparse, so this paper draws on examples of plant stem cutting. It reviews the factors that affect the plant stem cutting process. Among the, Cutting speed, blade sharpness, and moisture content, factors that can easily be controlled, are discussed. The indicators for evaluating the cutting process and the methods for measuring the influencing factors are introduced as well. Finally, different blade designs, examples of the application of mechanisms that affect the cutting process of plant stems are provided. This review argues that, under conditions of high cutting speed, high blade sharpness, and high moisture content, plastic deformation would be reduced and the stems would exhibit brittle material characteristics. This would help to reduce the cutting force and energy, but excessive brittleness can cause stem fragmentation and degrade cutting quality. This paper also lists some possible future research directions. First, friction behavior during the cutting process of fresh plant stems. Another, cutting blade design based on the comprehensive application of cutting speed, blade wedge angle, and sliding cutting angle on the cutting process. At present, the mechanism of plant stem cutting process is still not clear. Further research is needed.

A multiyear study was carried out at two citrus groves with mature trees in southwest Florida in the United States to evaluate the effects of cover cropping on the citrus interrow as a sustainable weed management strategy in the Florida citrus production system. Two cover crop (CC) mixes (legume + non-legume species and only non-legume species) were compared with a no-CC grower standard management (GSM) that utilized the herbicide paraquat for weed suppression in the citrus tree interrow spaces. We gathered data on the biomass and density of both CCs and weeds, during the spring and summer/fall CC planting seasons throughout the study years. Both mixes of CCs effectively reduced weed density in the citrus interrow by 58% to 99% (P < 0.05), depending on the growing season and study locations, compared with GSM. Additionally, there were no significant differences observed between the different CC mixes. Similarly, both CC mixes reduced the weed biomass by 95% to 99% (P < 0.05) in the citrus interrow compared with the GSM. However, weed suppression by CCs varied between growing seasons, mainly due to differences in germination and establishment of the CCs in each season.

Interrow weed control is used in a wide range of crops, traditionally applied via physical cultivation or banded herbicide application. However, these methods may result in crop damage, development of herbicide resistance, or off-target environmental impacts. Electric interrow weed control presents an alternative, although its potential impact on crop yield requires further investigation. One of the modes of action of electric weed control is the continuous electrode–plant contact method, which passes a current through the weed and into the roots. As the current passes into the roots, it can potentially disperse through the soil to neighboring root systems. Such off-target current dispersion, particularly in moist topsoil with low resistance, poses potential concern for neighboring crops when electric interrow weed control is applied. This research evaluated the continuous electrode–plant contact method, using a Zasso™ XPower machine, in comparison with mowing across three trials conducted in 2022 and 2023. Both treatments were used to remove target lupine (Lupinus albus L.) plants adjacent to a row of non-target lupine. Electric weed control was applied to plants in dry soil or following a simulated rainfall event. The trials demonstrated that electric weed control and mowing did not reduce density and biomass of neighboring non-target lupine plants compared with the untreated control. Likewise, pod and seed production, grain size, and protein, as well as grain germinability and vigor of the resulting seedlings, were not reduced by these weed control tactics. This research used technology that was not fit for purpose in broadscale grain crops but concludes that electric weed control via the continuous electrode–plant contact method or mowing did not result in crop damage. Therefore, it is unlikely that damage will occur using commercial-grade electric weed control or mowing technology designed for large-acreage interrow weed control, thus offering nonchemical weed management options.

Yellow nutsedge (Cyperus esculentus L.) is one of the most problematic weeds in turfgrass due to its fast growth rate and high tuber production. Effective long-term control relies on translocation of systemic herbicides to underground tubers. Two identical trials were conducted simultaneously in separate greenhouses to evaluate the effect of several acetolactate synthase (ALS)- and protoporphyrinogen oxidase (PPO)-inhibiting postemergence herbicides on C. esculentus tuber production and viability. Seven tubers were planted into 1-L pots, and plants were allowed to mature for 6 wk before trial initiation. Treatments included pyrimisulfan at 73 g ai ha−1 once or 49 g ai ha−1 twice, imazosulfuron at 736 g ai ha−1 once or 420 g ai ha−1 twice, carfentrazone-ethyl + sulfentrazone at 22 + 198 g ai ha−1 once or 14 + 127 g ai ha−1 twice, halosulfuron at 70 g ai ha−1 once or 35 g ai ha−1 twice, and a nontreated control. Sequential applications were made 3 wk after initial treatment (WAIT) for both trials. Both single and sequential applications of carfentrazone-ethyl + sulfentrazone exhibited the quickest control (80% to 83% 4 WAIT). Two applications of imazosulfuron resulted in the greatest reduction in tuber number (81%) and tuber dry biomass (85%), while one application of carfentrazone-ethyl + sulfentrazone resulted in the greatest reduction in shoot biomass (71%). The viability of tubers that were recovered from each pot was reduced 48% to 70%, with the greatest reduction in response to carfentrazone-ethyl + sulfentrazone. Although two applications of pyrimisulfan only resulted in tuber number and shoot biomass reductions of 66% and 38%, respectively, tuber dry biomass reduction was 80%. Therefore, pyrimisulfan, imazosulfuron, halosulfuron, and carfentrazone-ethyl + sulfentrazone are all viable options for long-term C. esculentus control in turfgrass.

Russian thistle (Salsola tragus L.) is a significant summer annual weed in the semiarid Pacific Northwest, causing yield losses of up to 50%. Understanding the biology and ecology of S. tragus is vital for developing effective integrated weed management strategies. This study focused on (1) S. tragus emergence and seedbank persistence in two cropping systems: fallow–winter wheat (Triticum aestivum L.) and spring wheat–fallow–winter wheat rotations, and (2) S. tragus plant biomass and viable seed production in fallow and spring wheat fields. A 4-yr experiment (2020 to 2023) was conducted at the Columbia Basin Agriculture Research Center in Adams, OR, using a randomized block design with four replications. Salsola tragus seeds were sprinkled only at the beginning of the experiment, and seedling numbers were recorded throughout. Most seedlings emerged in the first year, with the highest rates in spring wheat (72%) and fallow (32%), followed by significantly lower rates (0.25% to 5%) in subsequent years. Seedling emergence began in late March and early April in the first and second years but was delayed to May in the third year. Plant biomass and viable seed production were greater in fallow than in spring wheat, with early-season plants having more biomass than later-emerging plants. Plants emerged between early and mid-May produced the most viable seeds. Viable seed production was very low until it peaked in mid-September. Findings indicated that most S. tragus seedlings emerged in the first year after dispersal coinciding with spring precipitation and lasting approximately 2 mo. Additionally, most S. tragus plants produce viable seeds in September, and seeds persist in the soil for more than 2 yr. These results demonstrate the need for growers to control S. tragus emergence to prevent reinfestations and ultimately the need to control S. tragus plants before September to prevent the species from producing viable seed.

Transgressive segregation refers to the phenomenon whereby the progeny of a diverse cross exhibit phenotypes that fall outside the range of the parents for a particular trait of interest. Segregants that exceed the parental values in life-history traits contributing to survival and reproduction may represent beneficial new allelic combinations that are fitter than respective parental genotypes. In this research, we use geographically disparate paraquat-resistant biotypes of horseweed (Canada fleabane) [Erigeron canadensis L.; syn.: Conyza canadensis (L.) Cronquist] to explore transgressive segregation in biomass accumulation and the inheritance of the paraquat resistance trait in this highly self-fertilizing species. Results of this research indicate that the paraquat resistance traits in E. canadensis biotypes originating in California, USA, and Ontario, Canada, were not conferred by single major gene mechanisms. Segregating generations from crosses among resistant and susceptible biotypes all displayed transgressive segregation in biomass accumulation in the absence of the original selective agent, paraquat. However, when challenged with a discriminating dose of paraquat, progeny from the crosses of susceptible × resistant and resistant × resistant biotypes displayed contrasting responses with those arising from the cross of two resistant biotypes no longer displaying transgressive segregation. These results support the prediction that transgressive segregation is frequently expressed in self-fertilizing lineages and is positively correlated with the genetic diversity of the parental genotypes. When exposed to a new environment, transgressive segregation was observed regardless of parental identity or history. However, if hybrid progenies were returned to the parental environment with exposure to paraquat, the identity of the fittest genotype (i.e., parent or segregant) depends on the history of directional selection in the parental lineages and the dose to which the hybrid progeny was exposed. It is only in the original selective environment that the impact of allelic fixation on transgressive segregation can be observed.

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.

Annual bluegrass (Poa annua L.) populations in turfgrass have evolved resistance to several herbicides in the United States, but there has been no confirmed resistance from an agricultural field. Recently, glyphosate failed to control a P. annua population found in a field in a soybean [Glycine max (L.) Merr.] and rice (Oryza sativa L.) rotation in Poinsett County, AR. The present study focused on determining the sensitivity of a putatively resistant accession (R1) to glyphosate compared with two susceptible accessions (S1 and S2). The experiments included a dose–response study, 5-enolpyruvylshikimate-3-phosphate synthase (EPSPS) gene copy number and expression analysis, and assessment of mutations in EPSPS. Based on the dose–response analysis, R1 required 1,038 g ae ha−1 of glyphosate to cause 50% biomass reduction, whereas S1 and S2 only required 148.2 and 145.5 g ae ha−1, respectively. The resistance index (RI) was approximately 7-fold relative to the susceptible accessions. Real-time polymerase chain reaction data revealed at least a 15-fold increase in the EPSPS copy number in R1, along with a higher gene expression. No mutations in EPSPS were found. Gene duplication was identified as the main mechanism conferring resistance in R1. The research presented here reports the first incidence of glyphosate resistance in P. annua from an agronomic field crop situation in the United States.

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.

Seventeen putative resistant late watergrass populations [Echinochloa phyllopogon (Stapf.) Koso-Pol.; syn.: Echinochloa oryzicola (Vasinger) Vasinger] originating from rice (Oryza sativa L.) monoculture fields in northern Greece were examined for possible evolution of multiple resistance to acetolactate synthase (ALS) and acetyl-CoA carboxylase (ACCase) inhibitors and auxin herbicides in rate–response pot assays. Most of the populations were highly cross-resistant to the ALS-inhibiting herbicides bispyribac-Na, imazamox, penoxsulam, and nicosulfuron + rimsulfuron, whereas three of them were also multiple resistant to both ALS and the auxin mimic quinclorac. In addition, two E. phyllopogon populations were found to be multiple resistant to the ALS and ACCase inhibitors cycloxydim, cyhalofop-butyl, profoxydim, and quizalofop-P-ethyl. Amplification and sequencing of the ACCase gene fragment from eight surviving profoxydim-treated plants of the two multiple-resistant E. phyllopogon populations to ALS- and ACCase-inhibiting herbicides, revealed an Ile to Leu substitution at codon 1781 of the ACCase enzyme. However, amplification and sequencing of the ALS gene fragment in the same E. phyllopogon plants sequenced for ACCase revealed a Trp to Leu substitution at codon 574 of the ALS enzyme in three out of the eight sequenced plants. These results strongly support the evidence of coexisting E. phyllopogon multiple target-site resistance to ALS and ACCase inhibitors, which is reported for the first time.

Weed-suppression benefits of cover crops (CCs) have long been recognized; however, the specific ability of CCs to suppress highly epidemic Amaranthus spp. (Palmer amaranth (Amaranthus palmeri S. Watson), redroot pigweed (Amaranthus retroflexus L.), smooth pigweed (Amaranthus hybridus L.), and waterhemp [Amaranthus tuberculatus (Moq.) Sauer]) has not been widely discussed. The objective of this meta-analysis was to evaluate the implications of CC management decisions (CC type, planting and termination methods, residue fate after termination, and in-season weed management plan) on Amaranthus spp. weed density (ASWD) and Amaranthus spp. weed biomass (ASWB) compared with no CC (NCC) in temperate regions, including the United States and Canada. We found 41 studies conducted across the United States and Canada and extracted 595 paired observations. The results indicate that CCs reduced the ASWD by 58% in the early season (0 to 4 wk after crop planting [WAP]), by 48% in the midseason (5 to 8 WAP), and by 44% in the late season (>8 WAP). Similarly, CCs reduced ASWB by 59%, 55%, and 37% in the early, mid-, and late season, respectively. Meta-regression analysis showed CCs terminated within 2.5 wk of crop planting reduced ASWD by ≥50%. CC biomass required to reduce ASWD and ASWB by 50% was 4,079 kg ha−1 for ASWD and 5,352 kg ha−1 for ASWB. Among CC types, grasses and mixtures reduced ASWD by 60% and 77% in early season, 53% and 59% in midseason, and 44% and 47% in late season. Legume CCs were effective only during the early season (47% ASWD reduction), while brassicas did not affect ASWD. CC residues remaining on the soil surface were more effective for reducing ASWD than incorporation. CCs did not affect ASWD or ASWB compared with NCC when herbicides were used for in-season weed management. In general, CCs were found to reduce ASWD and ASWB and therefore can be used as an effective tool for integrated management of Amaranthus spp.

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.

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.