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.

Foliar-applied postemergence herbicides are a critical component of corn (Zea mays L.) and soybean [Glycine max (L.) Merr.] weed management programs in North America. Rainfall and air temperature around the time of application may affect the efficacy of herbicides applied postemergence in corn or soybean production fields. However, previous research utilized a limited number of site-years and may not capture the range of rainfall and air temperatures that these herbicides are exposed to throughout North America. The objective of this research was to model the probability of achieving successful weed control (≥85%) with commonly applied postemergence herbicides across a broad range of environments. A large database of more than 10,000 individual herbicide evaluation field trials conducted throughout North America was used in this study. The database was filtered to include only trials with a single postemergence application of fomesafen, glyphosate, mesotrione, or fomesafen + glyphosate. Waterhemp [Amaranthus tuberculatus (Moq.) Sauer], morningglory species (Ipomoea spp.), and giant foxtail (Setaria faberi Herrm.) were the weeds of focus. Separate random forest models were created for each weed species by herbicide combination. The probability of successful weed control deteriorated when the average air temperature within the first 10 d after application was <19 or >25 C for most of the herbicide by weed species models. Additionally, drier conditions before postemergence herbicide application reduced the probability of successful control for several of the herbicide by weed species models. As air temperatures increase and rainfall becomes more variable, weed control with many of the commonly used postemergence herbicides is likely to become less reliable.

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.

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.

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.

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.

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.

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.

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.

Multiple herbicide–resistant (MHR) kochia [Bassia scoparia (L.) A.J. Scott] is a concern for farmers in the Great Plains. A total of 82 B. scoparia populations were collected from western Kansas (KS), western Oklahoma (OK), and the High Plains of Texas (TX) during fall of 2018 and 2019 (from the various locations), and their herbicide resistance status was evaluated. The main objectives were to (1) determine the distribution and frequency of resistance to atrazine, chlorsulfuron, dicamba, fluroxypyr, and glyphosate; and (2) characterize the resistance levels to glyphosate, dicamba, and/or fluroxypyr in selected B. scoparia populations. Results indicated that 33%, 100%, 48%, 30%, and 70% of the tested B. scoparia populations were potentially resistant (≥20% survival frequency) to atrazine, chlorsulfuron, dicamba, fluroxypyr, and glyphosate, respectively. A three-way premixture of dichlorprop/dicamba/2,4-D provided 100% control of all the tested populations. Dose–response studies further revealed that KS-9 and KS-14 B. scoparia populations were 5- to 10-fold resistant to dicamba, 3- to 6-fold resistant to fluroxypyr, and 4- to 5-fold resistant to glyphosate as compared with the susceptible (KS-SUS) population. Similarly, OK-10 and OK-11 populations were 10- to 13-fold resistant to dicamba and 3- to 4-fold resistant to fluroxypyr and glyphosate compared with the OK-SUS population. TX-1 and TX-13 B. scoparia populations were 2- to 4-fold resistant to dicamba, and TX-1 was 5-fold resistant to glyphosate compared with the TX-SUS population. These results confirm the first report of dicamba- and fluroxypyr-resistant B. scoparia from Oklahoma and glyphosate- and dicamba-resistant B. scoparia from Texas. These results imply that adopting effective integrated weed management strategies (chemical and nonchemical) is required to mitigate the further spread of MHR B. scoparia in the region.

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.

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.

Tetflupyrolimet (Dodhylex™ Active, FMC Corporation) is a novel herbicide inhibiting de novo pyrimidine biosynthesis that controls grassy weeds preemergence in rice (Oryza sativa L.) production. Field trials were conducted from 2021 to 2024 to evaluate turfgrass tolerance to tetflupyrolimet applications for annual bluegrass (Poa annua L.) and smooth crabgrass [Digitaria ischaemum (Schreb.) Schreb. ex Muhl.] control. Tolerance was evaluated on seven turfgrass species, including creeping bentgrass (Agrostis stolonifera L.), Kentucky bluegrass (Poa pratensis L.), tall fescue [Schedonorus arundinaceus (Schreb.) Dumort.; syn.: Festuca arundinacea Schreb.], hybrid bermudagrass [Cynodon dactylon (L.) Pers. × Cynodon transvaalensis Burtt-Davy], and manilagrass [Zoysia matrella (L.) Merr.] at various mowing heights ranging from 3.8 to 12.5 mm. Separate experiments were conducted on each turfgrass species to evaluate tolerance in both fall and spring. Tetflupyrolimet was applied at rates of 0, 25, 50, 100, 200, 400, 800, 1600, 3200, or 6400 g ai ha–¹. No injury was observed on any warm-season turfgrass species in either season, whereas cool-season grass tolerance varied among species each season; however, cool-season turfgrass tolerance for all species was greater in spring than fall. While efficacy of tetflupyrolimet (400 g ha–¹) for preemergence D. ischaemum control varied among years, mixtures of tetflupyrolimet (400 g ha–¹), pyroxasulfone (128 g ai ha–¹), and rimsulfuron (35 g ai ha–¹) applied preemergence or early postemergence effectively controlled multiple-resistant P. annua in both seasons. Overall, these findings highlight that warm-season turfgrasses are highly tolerant of tetflupyrolimet applications for P. annua or D. ischaemum control.

Trifludimoxazin is a new herbicide that inhibits protoporphyrinogen oxidase (PPO) and is targeted for commercial market introduction in North America, South America, and Asia. It will be available both as a stand-alone product and in a 1:2 mixture with saflufenacil. The herbicide is intended for use in preplant burndown and preemergence applications in cereal, corn (Zea mays L.), soybean [Glycine max (L.) Merr.], and pulse crops to control a variety of annual broadleaf and grass weed species. Additionally, it is intended to be used in tree crops, oil palm (Elaeis guineensis Jacq.), and non-crop areas. In this study, we meticulously evaluated the performance and effectiveness of both the stand-alone herbicide and the innovative mixture concept in combating prevalent weeds commonly encountered in corn and soybean fields. Our findings revealed that both products exhibited exceptional efficacy, significantly reducing the presence of these troublesome weeds. Furthermore, the mixture concept not only demonstrated commendable soil mobility but also showcased impressive residual activity, positioning it as a powerful tool for sustainable weed control. These promising effects are further substantiated by our comprehensive adsorption–distribution–metabolism–extraction (ADME) studies, which provide insight into the behavior and longevity of the herbicides in the agricultural ecosystem.

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 (LD_50, 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.

Italian ryegrass [Lolium perenne L. ssp. multiflorum (Lam.) Husnot] has become a major annual weed in wheat (Triticum aestivum L.) production systems in the inland Pacific Northwest. With large genetic variability and abundant seed production, L. perenne ssp. multiflorum has developed globally 74 documented cases of herbicide resistance covering 8 different mechanisms of action. Harvest weed seed control (HWSC) systems were introduced in Australia in response to the widespread evolution of multiple herbicide resistance in rigid ryegrass (Lolium rigidum Gaudin) and wild radish (Raphanus raphanistrum L.). The efficacy of these systems for any given weed species is directly related to the proportion of total seed retained by that species at harvest time. From 2017 to 2020, ten L. perenne ssp. multiflorum plants were collected from three different slope aspects at each location in Washington, USA. Collections were initiated in each field when it was visually apparent that seed fill was nearly complete, and seed shatter had not yet occurred. Collection continued at near-weekly intervals until the fields were harvested. The number of filled florets on a spikelet was used to assess the degree of seed shatter over time. Seed shatter at harvest was 67% of the total number of florets on each spikelet. Seed shatter was closely aligned with wheat kernel development in both spring and winter wheat. The high percentage of L. perenne ssp. multiflorum seeds that are shattered by harvest may make HWSC less effective than for L. rigidum in Australia; however, seeds with the greatest biomass tend to not shatter before harvest, which may increase the efficacy of HWSC for managing the soil seedbank. Strategies like planting earlier-maturing wheat cultivars could help HWSC be more effective by having wheat harvest begin earlier, when more L. perenne ssp. multiflorum seeds are still on the mother plant.

Furrow-irrigated rice (Oryza sativa L.) hectares are increasing in the Midsouth. The lack of sustained flooding creates a favorable environment for weed emergence and persistence, which makes Palmer amaranth (Amaranthus palmeri S. Watson) difficult to control throughout the growing season. The negative yield impacts associated with season-long A. palmeri interference in corn (Zea mays L.), cotton (Gossypium hirsutum L.), and soybean [Glycine max (L.) Merr.] have been evaluated. However, there is limited knowledge of the weed's ability to influence rice grain yield. Research was initiated in 2022 and 2023 to determine the effect of A. palmeri time of emergence relative to rice on weed seed production and grain yield. Cotyledon-stage A. palmeri plants were marked every 7 d, beginning 1 wk before rice emergence through 4 wk after rice emergence. Amaranthus palmeri seed production decreased exponentially as emergence timing was delayed relative to rice, and seed production increased by 447 seed plant^–1 for every 1-g increase in weed biomass. Without rice competition and from the earliest emergence timing, A. palmeri produced 540,000 seeds plant^–1. Amaranthus palmeri that emerged 1 wk before the crop had the greatest spatial influence on rice, with grain yield loss of 5% and 50% at a distance of 1.4 m and 0.40 m from the weed, respectively. As A. palmeri emergence was delayed, the area of influence decreased. However, A. palmeri plants emerging 3.5 wk after rice emergence still negatively affected grain yield and produced sufficient seed to replenish the soil seedbank, potentially impacting long-term crop management decisions. These results show that the time of A. palmeri emergence is a crucial factor influencing rice grain yield and weed seed production, which can be used to determine the consequences of escapes in rice.

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.

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.

The rapid and efficient removal of weeds is currently a research hotspot. With the integration of robotics and automation technology into agricultural production, intelligent field-weeding robots have emerged. An overview of the development status of weeding robots based on bibliometric and scientific mapping methods is presented. Two key technologies of weeding robots are summarized, and the research progress of precision-spraying weeding robots, mechanical weeding robots, and thermal weeding robots with laser devices, categorized by weeding method, is reviewed. Finally, a summary and an outlook on the future development trends of intelligent field-weeding robots are provided, aiming to offer a reference for further promoting the development of weeding robots.

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.

Kochia [Bassia scoparia (L.) A.J. Scott] is an invasive tumbleweed in the North American Great Plains that is difficult to manage in croplands and ruderal areas due to widespread resistance to up to four herbicide sites of action, including auxin mimics (Herbicide Resistance Action Committee [HRAC] Group 4) and inhibitors of acetolactate synthase (HRAC Group 2), photosystem II (HRAC Group 5), and 5-enolpyruvylshikimate-3-phosphate synthase (HRAC Group 9). Poor B. scoparia control with protoporphyrinogen oxidase (PPO)-inhibiting (HRAC Group 14) herbicides was noted in a brown mustard [Brassica juncea (L.) Czern.] field near Kindersley, SK, Canada, in 2021. Similar observations were made in a sunflower (Helianthus annuus L.) field near Mandan, ND, USA, and in research plots near Minot, ND, USA, in 2022. Whole-plant dose–response experiments were conducted to determine whether these B. scoparia accessions were resistant to the PPO-inhibiting herbicides saflufenacil and carfentrazone and the level of resistance observed. All three B. scoparia accessions were highly resistant to foliar-applied saflufenacil and carfentrazone compared with two locally relevant susceptible accessions. The Kindersley accession exhibited 57- to 87-fold resistance to saflufenacil and 97- to 121-fold resistance to carfentrazone based on biomass dry weight at 21 d after treatment (DAT). Similarly, the Mandan accession exhibited 204- to 321-fold resistance to saflufenacil and 111- to 330-fold resistance to carfentrazone, while the Minot accession exhibited 45- to 71-fold resistance to saflufenacil and 88- to 264-fold resistance to carfentrazone. Substantial differences in visible control at 7 and 21/28 DAT were also observed between the putative-resistant and susceptible accessions. This study represents the first confirmations of PPO inhibitor–resistant B. scoparia globally and the fifth herbicide site of action to which B. scoparia has evolved resistance. It also documents this issue present at three locations in the Northern Great Plains region that occur up to 790 km apart and on both sides of the Canada/U.S. border.

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.

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.

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.

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.

Foliar-applied postemergence applications of glufosinate are often applied to glufosinate-resistant crops to provide nonselective weed control without significant crop injury. Rainfall, air temperature, solar radiation, and relative humidity near the time of application have been reported to affect glufosinate efficacy. However, previous research may have not captured the full range of weather variability to which glufosinate may be exposed before or following application. Additionally, climate models suggest more extreme weather will become the norm, further expanding the weather range to which glufosinate can be exposed. The objective of this research was to quantify the probability of successful weed control (efficacy ≥85%) with glufosinate applied to some key weed species across a broad range of weather conditions. A database of >10,000 North American herbicide evaluation trials was used in this study. The database was filtered to include treatments with a single postemergence application of glufosinate applied to waterhemp [Amaranthus tuberculatus (Moq.) Sauer], morningglory species (Ipomoea spp.), and/or giant foxtail (Setaria faberi Herrm.) <15 cm in height. These species were chosen because they are well represented in the database and listed as common and troublesome weed species in both corn (Zea mays L.) and soybean [Glycine max (L.) Merr.] (Van Wychen 2020, 2022). Individual random forest models were created. Low rainfall (≤20 mm) over the 5 d before glufosinate application was detrimental to the probability of successful control of A. tuberculatus and S. faberi. Lower relative humidity (≤70%) and solar radiation (≤23 MJ m^–1 d–¹) on the day of application reduced the probability of successful weed control in most cases. Additionally, the probability of successful control decreased for all species when average air temperature over the first 5 d after application was ≤25 C. As climate continues to change and become more variable, the risk of unacceptable control of several common species with glufosinate is likely to increase.

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.

Established hedgerows of native plants on the borders of crop fields provide a variety of ecosystem service benefits in agricultural landscapes. However, their influence on weed communities is not well understood, and there are concerns that hedgerows could contribute to weed infestations on farms. To address this research gap, we examined the role of established hedgerows of native California plants on weed abundance (weed numbers and cover) and weed species richness in field borders, and in adjacent crops, in large-scale, monocropping systems compared with conventionally managed field borders (i.e., no hedgerows). Across 20 farm sites in California's Central Valley, hedgerows on orchard crop borders reduced weed numbers by 66%, weed species richness by 59%, and weed cover by 74%. On annual field crop borders, hedgerows reduced weed numbers by 71%, weed species richness by 60%, and weed cover by 70%. In orchards, hedgerows also reduced weed intrusion into the adjacent crop interior, with significantly lower weed cover to the first tree row (area directly underneath the trees), weed species richness to the 10-m tree row, and weed numbers to the 10-m avenue (area between the tree rows). Yearly management practices and associated costs for weed control in established hedgerows were significantly less than for conventionally managed field borders. This study highlights the effectiveness of native hedgerows as a sustainable nature-based solution for reducing weed pressure and management inputs on farms.

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.

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.

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.

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.

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.

Residual herbicides are primarily degraded in the soil through microbial breakdown. Any practices that result in increased soil biological activity, such as cover cropping (between cash crop seasons), could lead to a reduced persistence of herbicides in the soil. Furthermore, cover crops can also interfere with herbicide fate by interception. Field trials were conducted between 2020 and 2023 in a corn (Zea mays L.)–soybean [Glycine max (L.) Merr.] rotation to investigate the influence of cover crop (cereal rye [Secale cereale L.] and crimson clover [Trifolium incarnatum L.]) use on soil enzyme activities (β-glucosidase [BG] and dehydrogenase [DHA]), its effect on the concentration of residual herbicides (sulfentrazone, S-metolachlor, cloransulam-methyl, atrazine, and mesotrione) in the soil, and the interception of herbicides by cover crop residue. The use of cover crops occasionally resulted in increased BG and DHA activities relative to the fallow treatment. However, even when there was an increase in the activity of these two enzymes, increased degradation of the residual herbicides was not observed. The initial concentrations of all residual herbicides in the soil were significantly reduced due to interception by cereal rye biomass. Nevertheless, significant reductions in early-season weed biomass were observed when residual herbicides were included in the tank mixture applied at cover crop termination relative to the application of glyphosate plus glufosinate. Results from this research suggest that the use of cereal rye or crimson clover as cover crops (between cash crop seasons) do not impact the persistence of residual herbicides in the soil or reduce their efficacy in controlling weeds early in the growing season.

Seed impact mills like the Redekop Seed Control Unit (SCU) and the integrated Harrington Seed Destructor (iHSD) have the potential to fit within the U.S. wheat (Triticum aestivum L.) production system, but they may be affected by changes in crop yield and harvest residue moisture, which can have an impact on chaff flow rate and chaff moisture, respectively. This research aimed to determine the seed kill of problematic weed species and how varying chaff flow rates and chaff moisture affect seed kill and horsepower draw of the SCU and the iHSD. Four different chaff flow rates were tested at 0.75, 1.5, 2.25, and 3.0 kg s^–1, which span 0.5× to 2× of a combine's standard throughput. Additionally, four chaff moisture contents were tested at 10.7%, 16.4%, 22.1%, and 27.8%, which span and exceed typical harvest conditions. Results indicated that >91% of all weed seeds of the tested species were killed by either mill. Seed kill decreased by 7.9% and 0.08% for every 1-kg increase in chaff flow rate for Italian ryegrass [Lolium perenne L. ssp. multiflorum (Lam.) Husnot] and hairy vetch (Vicia villosa Roth), respectively, for the iHSD. Seed kill also decreased by 3.4% for every 1-kg increase in chaff flow rate for weedy L. perenne ssp. multiflorum for the SCU. Increasing chaff moisture resulted in seed kill decreasing by 0.43% and 0.015% for every 1% increase in chaff moisture for weedy L. perenne ssp. multiflorum and volunteer canola (Brassica napus L.), respectively, with the SCU. Both chaff flow rate and chaff moisture had a significant effect on horsepower draw for both mills compared with an empty mill. Despite the increase in horsepower draw and the decrease in seed kill, these data indicate the potential for seed impact mills to operate in less than ideal conditions while still providing seed kill rates >74%.

Combine modifications for harvest weed seed control like the Redekop Seed Control Unit (SCU) and the integrated Harrington Seed Destructor (iHSD) have been successfully used to kill problematic weed seeds in small grain production in Australia. These seed impact mills could have a fit in U.S. soybean [Glycine max (L.) Merr.] production. Testing the seed kill rate of problematic weed species in soybean is important for confirming the efficacy of the mills. Additionally, the mills may be affected by changes in crop yield and harvest residue moisture, which can have an impact on chaff flow rate and chaff moisture, respectively. This research aimed at determining the seed kill percent for problematic weeds and how varying chaff flow rates and chaff moisture content in soybean chaff affect the seed kill rate and horsepower draw of two different impact mills, the Redekop SCU and the iHSD. All testing was conducted using stationary test stands. Chaff flow rate and chaff moisture levels tested ranged from 0.5× to 2× standard combine throughput and 11.7% to 28.6% moisture, respectively. All tested species were killed at >98% by both mills. Increasing chaff flow rate resulted in a decrease in seed kill for all tested species with the iHSD and only common ragweed (Ambrosia artemisiifolia L.) with the Redekop SCU. Increasing chaff moisture only resulted in a decrease in seed kill for Palmer amaranth (Amaranthus palmeri S. Watson) with the iHSD. Data evaluating the horsepower needed to power the mills also indicated that chaff flow rate and chaff moisture resulted in a significant increase in horsepower draw. With generally high kill rates (>98%) and the ability to kill weed seeds at >98% in less than ideal harvest conditions (i.e., high-moisture chaff), seed impact mills could be used in soybean production to reduce weed seed inputs into the soil seedbank during harvest.

The changing climate, land use, and agronomic practices are driving shifts in weed biology and management across Australia's grain production systems. A stakeholder survey was conducted to identify key weed species, adaptations, and factors influencing future research priorities in three major cropping regions. The most problematic and adaptive species included rigid ryegrass (Lolium rigidum Gaudin), hairy fleabane [Conyza bonariensis (L.) Cronquist; syn.: Erigeron bonariensis L.], Bromus spp. (ripgut brome [Bromus diandrus Roth; syn.: Bromus rigidus Roth]), annual sowthistle (Sonchus oleraceus L.), wild radish (Raphanus raphanistrum L.), and feather fingergrass (Chloris virgata Sw.). These weeds also ranked high for future research focus. Observed adaptive traits included changes in dormancy and emergence patterns, shifts in phenology, and a shift toward year-round growth driven by warmer winters and increased summer rainfall. Regional responses varied slightly, with soil and crop management practices ranked as the primary driver of changing weed biology (88%), followed by climatic factors (56%), while soil factors (13%) were not considered to be significant. Participants in the Northern region highlighted climate change (67%) as a major driver, while those in the Western region emphasized management practices (95%) and soil-related factors (32%). Sixty percent of participants noted that climatic changes were introducing new weeds, and 69% believed that changing weed biology was reducing control efficacy. National research priorities included understanding weed emergence dynamics (73%), effects of climate on herbicide efficacy (71%), and better understanding of weed ecology (68%). These findings highlight the trends in weed evolution and need for future research on changing weed biology and adaptive management strategies. Surveys of agronomists, farm advisors, researchers, and farmers provide a cost-effective method to monitor new weed adaptations. Refining survey methodologies and enhancing field data collection could improve the ability to track and manage weed adaptations to shifts in climate and management practices.

The widespread distribution of wolf poison (Stellera chamaejasme L.), spanning from southern Russia to southwestern China and the western Himalayas, contributes to its prevalence as an invasive species in grassland ecosystems. Its extensive range, coupled with its ability to thrive in harsh environments, enables it to rapidly colonize grasslands. Once established, it rapidly spreads and dominates large areas. This process inevitably leads to grassland degradation over time, thereby exerting significant impacts on both ecology and economy. In China, grasslands (26.45 million ha, 27.5% of land area) face severe degradation, with more than 90% impacted by overgrazing and climate change. Stellera chamaejasme infestations exceed 1.4 million ha in Qinghai, 546,700 ha in Gansu, and 133,000 ha in Inner Mongolia, causing annual forage losses of 137,500 Mg and economic damages of 15 to 20 million yuan in Gansu alone. These impacts threaten ecosystem stability and pastoral livelihoods. Therefore, research on the mechanisms of spread of invasive plants is crucial. In this comprehensive description, we investigated the effects of S. chamaejasme on plant communities and herbivore interactions. Our research showed how this species successfully invades grasslands and establishes itself as a dominant species. Stellera chamaejasme enhances its expansion by altering soil physicochemical properties, reducing nutrient cycling, and increasing pathogenic fungi abundance while enhancing microbial diversity, creating self-favoring soil conditions. With high genetic diversity, robust reproductive capacity, and potent allelopathic effects, it suppresses neighboring vegetation and escapes herbivory due to toxicity, accelerating invasion. These interrelated traits facilitate the rapid invasion and spread of S. chamaejasme on grasslands, ultimately leading to its dominance. This trend poses a significant threat to the health and stability of the grassland ecosystem. Future research should delve into the ecological adaptability and allelopathic mechanisms of S. chamaejasme, aiming to develop effective management strategies for controlling its spread and promoting grassland recovery and biodiversity conservation.

Sterile oat [Avena sterilis L. ssp. ludoviciana (Durieu) Gillet & Magne] is rapidly proliferating in cereal fields across northeastern and northwestern Iran, underscoring the necessity of studying its ecology in these two distinct climates. A study was conducted to assess the impact of environmental factors on the germination of two native populations of A. sterilis. The germination responses of populations from Mashhad (northeastern Iran) and Tabriz (northwestern Iran) were evaluated under various treatments, including temperature, osmotic potential, NaCl concentration, and light/dark cycles. As the temperature increased and osmotic potential decreased—indicating heightened drought stress—the germination percentages of both populations declined. The Mashhad population exhibited the highest germination percentages, reaching 99% at 10 C and 100% at 15 C, both under 0 MPa osmotic potential. Conversely, the Tabriz population demonstrated its peak germination percentages at 15 C and 20 C, also under 0 MPa osmotic potential, with rates of 97% and 96%, respectively. The highest germination rates were observed in seeds from the Mashhad and Tabriz populations at 15 C, with osmotic potentials of 0 MPa and –0.3 MPa, yielding rates of 0.52 and 0.48 seeds d–¹, respectively. The NaCl concentration required for 50% inhibition of seed germination was 4.76 dS m^–1 for the Mashhad population and 3.90 dS m^–1 for the Tabriz population. In both populations, the highest germination percentage was observed under a light/dark cycle of 10 h of light and 14 h of darkness. The differences in germination responses between the Mashhad and Tabriz populations can be attributed to local environmental adaptations. Variations in temperature, osmotic potential, and other climatic factors influence seed dormancy and germination traits, enabling populations to thrive in their specific habitats. These local adaptations contribute to differences in germination performance under various environmental conditions, ultimately affecting their potential spread across different regions.

Weed management practices in agroecosystems mainly rely on herbicide, mowing, or tillage. Electric weed control offers a novel alternative, with a range of commercially available products for weed management in agricultural environments. However, electrical weed control efficacy has not been effectively compared with conventional weed management practices. Further, electrical weed control products may have a fire risk, as highlighted but not assessed in prior studies. The current study evaluated an electric weed control machine (Zasso^™ XPower) for weed management in four vineyard sites (in 2022 and 2023) in comparison to mowing and herbicide applications. Weed control tactics were applied in spring from budbreak to when shoots were approximately 10-cm long at EL growth stage 12. At an application speed of 1.1 to 1.4 km h^–1, averaged across the four sites, electric weed control at 24 or 36 kW reduced weed biomass by 84% to 87%, herbicide reduced biomass by 88%, and mowing reduced biomass by 65%. An assessment of vine normalized difference vegetation index indicated no differences in grapevine (Vitis vinifera L.) canopy development (i.e., no evidence of damage to vines) after each treatment. To assess fire risk, the same machine was used at a separate field site to apply electric weed control to bare ground with varying levels of dry plant biomass. Electric weed control in the presence of completely dry plant biomass did pose a significant fire risk (average of 0.37 incidences of smoke/flame m^–2). This technology is therefore not suitable for use in hot conditions where plant residue is dry. However, application in vineyards in the spring resulted in no evidence of fire. Our results, being the first of their kind, highlighted electric weed control as a potential alternative to chemical use that can be integrated into weed management programs in winter and spring within a Mediterranean climate.

Wild Mexican sunflower [Tithonia tubaeformis (Jacq.) Cass.] is one of the most important annual weeds for sugarcane (Saccharum spp. hybrid) and, to a lesser extent, for soybean [Glycine max (L.) Merr.] and bean (Phaseolus vulgaris L.) in the northwest of Argentina and some other countries. Currently, its management relies on chemical methods, and no information is available to develop alternative management methods. In the current study, we conducted laboratory germination assays in the presence of different conditions of light, temperature, and phytohormone (gibberellins and abscisic acid) concentrations, as well as fluridone, trinexapac-ethyl (TE), methyl viologen (MV), dry afterripening (DAR), cold stratification, and pericarp scarification. Likewise, a field experiment was carried out to assess the impact of various sugarcane crop residue amounts on seedling emergence. Darkness and constant temperatures (e.g., 20 C) reduced the germination of fresh seeds. The addition of TE, a gibberellic acid inhibitor, and abscisic acid reduced germination. In contrast, the addition of MV increased germination. Pericarp scarification and embryo excision stimulated germination, suggesting that the pericarp acts as a barrier to prevent germination. DAR did not promote germination. On the other hand, cold stratification enabled dormancy release, which in turn promoted germination when the stratified achenes germinated in light and at alternating temperatures of 20/30 C. Field experiments showed that increasing amounts of sugarcane crop residue were useful to reduce weed seedling emergence and biomass, probably by limiting the triggering effect of light and temperature alternation on seedling emergence. These findings provide information about the endogenous control of germination, which can be useful for developing a rational integrated management system for T. tubaeformis.

The mobility of a weed species is a strong determinant of the optimal management strategy, including whether area-wide management will be beneficial. In this paper, we examine the mobility and dispersal distances of flaxleaf fleabane [Conyza bonariensis (L.) Cronquist; syn.: Erigeron bonariensis L.], widely regarded as a highly mobile weed. We sampled individual weeds from two regions and sampled the same sites in the following season to conduct parentage analysis and assess intergenerational dispersal distances. We find high values of F_IS across populations consistent with mostly self-fertilization, but also relatively high genotypic diversity, suggesting that outcrossing does occur at low rates. We find evidence for long-distance dispersal (more than 350 km) and detect dispersal distances of up to 71 km and 36 km within each of the two regions using parentage analysis. We also find high spatial genetic structure within the Riverina region, with sites in 2021 genetically very similar to sites in 2020, indicating that local dispersal may be a more important driver of population genetics than long-distance dispersal, perhaps due to the high rates of seed production and self-fertilization. Glyphosate resistance was not spatially structured in C. bonariensis in these regions, highlighting the role of movement, and significant proportions of susceptible plants were found in both regions. The high levels of mobility, including over potentially long distances, indicate that the value of control and preventing weed seed set is likely to extend beyond the farm and offer “area-wide” benefit.

Automatic precision herbicide application offers significant potential for reducing herbicide use in turfgrass weed management. However, developing accurate and reliable neural network models is crucial for achieving optimal precision weed control. The reported neural network models in previous research have been limited by specific geographic regions, weed species, and turfgrass management practices, restricting their broader applicability. The objective of this research was to evaluate the feasibility of deploying a single, robust model for weed classification across a diverse range of weed species, considering variations in species, ecotypes, densities, and growth stages in bermudagrass turfgrass systems across different regions in both China and the United States. Among the models tested, ResNeXt152 emerged as the top performer, demonstrating strong weed detection capabilities across 24 geographic locations and effectively identifying 14 weed species under varied conditions. Notably, the ResNeXt152 model achieved an F₁ score and recall exceeding 0.99 across multiple testing scenarios, with a Matthews correlation coefficient (MCC) value surpassing 0.98, indicating its high effectiveness and reliability. These findings suggest that a single neural network model can reliably detect a wide range of weed species in diverse turf regimes, significantly reducing the costs associated with model training and confirming the feasibility of using one model for precision weed control across different turf settings and broad geographic regions.

Weed seeds are potential contaminants of composts derived from biowastes. We assessed the effect of steam treatment alone and in combination with composting on the mortality of barnyardgrass [Echinochloa crus-galli (L.) P. Beauv.] seeds in a biowaste substrate consisting of a mixture of onion (Allium spp.) waste (60%), horse (Equus spp.) manure (20%), and wood shavings (20%). In the first study, seeds of six populations of E. crus-galli exposed to temperatures ranging from ca. 60 to 99 C followed by a 3-min residence time exhibited a decline in seed germination from approximately 25% to 0%. The E. crus-galli populations varied greatly in germinability and responded differently to high temperatures. Samples with lower germinability as assessed in controls were killed at lower temperatures than samples with higher initial germinability. However, to ensure an almost 100% kill of all seeds in the populations, a mean temperature of 100 C was necessary. In another study, seed germination was assessed after steaming the biowaste mixture to a mean temperature of about 60 C and subsequently composting. A short steaming period of the biowaste mixture at approximately 60 C before composting was unnecessary, as all composted seed samples, including the non-steamed control seeds, died during the composting process.

Plants in the genera Astragalus and Oxytropis, collectively referred to as “locoweeds,” contain swainsonine, a toxic alkaloid synthesized by their fungal endophyte Alternaria sect. Undifilum. The ecological role of this endophyte across the mutualism–commensalism–parasitism continuum is unknown. We examined the fitness traits of Astragalus and Oxytropis species growing with and without the endophyte, in a 9-yr, common-garden experiment. Silky crazyweed (Oxytropis sericea Nutt.) and woolly loco (Astragalus mollissimus Torr.) plants germinated from seeds that naturally host the endophyte (E+) and with it mechanically removed (E–) were established in a common garden in southwest Montana. We measured mortality, gas exchange, flower and seed production, seed germination, and final biomass. Astragalus mollissimus plants grew as annuals under common-garden conditions regardless of endophyte status. Oxytropis sericea plants grew as perennials with survival unaffected by endophyte; however, E+ O. sericea plants produced slightly more reproductive stems, flowers per stem, and crown and stem biomass. Maternal effects detected in the parental generation disappeared in subsequent generations. Gas exchange, fecundity, and seed germination were unaffected by endophyte. Contrary to our initial hypothesis of mutualism, the endophyte did not improve host survival or fecundity, nor did we detect transgenerational effects. However, the endophyte did slightly increase the number of reproductive stems and flowers per stem and crown and stem mass in O. sericea, suggesting endophytic effects on carbohydrate biochemistry and pollination parameters should be examined. Lack of selection for or against endophyte-containing plants allows both nontoxic and toxic swainsonine-producing plants to persist in Astragalus and Oxytropis populations, posing a continued threat to grazing livestock.

Cattle (Bos spp.) grazing on weed–mixed forage biomass may potentially spread weed seeds, leading to plant invasions across pasturelands. Understanding the possibility and intensity of this spread is crucial for developing effective weed control methods in grazed areas. This research undertook an in vitro experiment to evaluate the germination and survival of five dominant weed species in the southern United States [Palmer amaranth (Amaranthus palmeri S. Watson), yellow foxtail [Setaria pumila (Poir.) Roem. & Schult.], johnsongrass [Sorghum halepense (L.) Pers.], field bindweed (Convolvulus arvensis L.) and pitted morningglory (Ipomoea lacunosa L.)] upon incubation in rumen fluid for eight time periods (0, 4, 8, 12, 24, 24, 48, 72, and 96 h). For the 96-h treatment, a full Tilley and Terry procedure was applied after 48 h for stopping fermentation, followed by incubation for another 48 h simulating abomasum digestion. Seed germination, upon incubation, varied significantly among weed species, with I. lacunosa reaching zero germination after only 24 h of incubation, whereas A. palmeri and S. halepense retained up to 3% germination even after 96 h of incubation. The hard seed coats of A. palmeri and S. halepense likely made them highly resistant, whereas the I. lacunosa seed coat became easily permeable and ruptured under rumen fluid incubation. This suggests that cattle grazing can selectively affect seed distribution and invasiveness of weeds in grazed grasslands and rangelands, including the designated invasive and noxious weed species. As grazing is a significant component in animal husbandry, a major economic sector in the U.S. South, our research provides important insights into the potential role of grazing as a dispersal mechanism for some of the troublesome arable weeds in the United States. The results offer opportunities for devising customized feeding and grazing practices combined with timely removal of weeds in grazeable lands at the pre-flowering stage for effective containment of weeds.

Branched broomrape [Phelipanche ramosa (L.) Pomel], a parasitic weed with a broad host range, is a quarantine pest in California. Phelipanche ramosa plants can produce thousands of tiny seeds that are easily spread by farm equipment. Best management practices for reducing dispersal risk include physical cleaning and disinfestation of farm equipment, but data on the efficacy of sanitizers on weed seeds are limited. A three-phase study was undertaken during 2022 to 2023 to evaluate quaternary ammonium compound (QAC) sanitizer efficacy on P. ramosa seed germinability. First, several QAC ingredients were evaluated at various concentrations (0 to 2.5 g per 100 ml) and exposure durations (1, 3, and 5 min) to develop initial germination curves. Second, the experiments were conducted with three commercial QAC sanitizers (MG4-Quat [Mg4], Flo-Quat, and Cleaner QT-185) at the recommended dose (1% v/v) and a field-relevant exposure duration (1 min). The final experiments evaluated commercial QAC sanitizer efficacy in the presence of various debris types. The initial experiments showed that alkyl dimethyl benzyl ammonium chloride (ADAC), didecyl dimethyl ammonium bromide (DDAB), and didecyl dimethyl ammonium chloride (DDAC) effectively prevented P. ramosa germination, but the effective dose for a 50% reduction in P. ramosa seed germination ranged from 0.001% (g per 100 ml) at 10 min with DDAC to 0.35% (g per 100 ml) at 1 min with ADAC. While all three QAC sanitizers reduced seed germination 75% to 100% after a 1-min exposure to the recommended dose (1% v/v), this treatment did not affect seed germination in the presence of soil (100 mg ml^-1) or fruit/plant tissue (40 mg ml^-1). At higher concentrations of Mg4 (8% v/v), P. ramosa seed germination was reduced by 90% to 100%, even in the presence of soil and plant debris. This study demonstrates that while QAC sanitizers can reduce P. ramosa seed germinability, their efficacy is compromised in the presence of debris. Therefore, physical cleaning to reduce debris loads before QAC application is essential for reducing the risk of P. ramosa seed movement among fields on equipment.

Indaziflam (Rejuvra®), a preemergence herbicide first registered in vine and tree nut crops, was recently approved for applications to rangeland for winter annual grass control. Indaziflam controls cheatgrass (Bromus tectorum L.) for at least 3 yr, and control can extend into a fourth and fifth year; however, it is very difficult to find indaziflam residues in the soil 2 yr after application. Indaziflam could be absorbed by seeds still retained on the plant and on the soil surface in sufficient concentrations to stop establishment. To test this hypothesis, B. tectorum seeds and jointed goatgrass (Aegilops cylindrica Host) spikelets were treated with indaziflam and imazapic at rates from 5.4 to 175 g ai ha^–1 using a greenhouse track sprayer delivering 187 L ha^–1. Treated seeds were planted into field soil, and plants were allowed to grow for 21 d under greenhouse conditions. Growth was compared with growth of non-treated controls. In addition, a second set of treated seeds were exposed to rainfall 1 and 24 h after treatment and rainfall amounts ranging from 3 to 24 mm to determine whether rainfall impacted herbicide performance. Bromus tectorum was so sensitive to indaziflam that establishment was eliminated at all rates. Imazapic inhibited B. tectorum establishment with an ED₉₀ of 67 g ai ha^–1. Indaziflam effectively inhibits A. cylindrica establishment with an ED₉₀ of 7.4 g ai ha^–1 compared with imazapic with an ED₅₀ of 175 g ai ha^–1. Indaziflam's impact on A. cylindrica establishment was not significantly impacted by rainfall, indicating that the herbicide was absorbed to the seed coat. These findings support the hypothesis that indaziflam's long-term control could result from its ability to inhibit establishment of seeds retained in the canopy and those on the soil surface at the time of application.