Glufosinate-ammonium (GA) has been widely used in Midwest fields, and in recent years a growing number of failures to control waterhemp [Amaranthus tuberculatus (Moq.) Sauer] have raised concerns about the evolution of resistance. The goal of this study was to investigate four cases of suspected resistance to GA in A. tuberculatus from Illinois using greenhouse, field, and transcriptomics studies. Greenhouse dose-response experiments revealed resistance ratios ranging from 2.2- to 3.4-fold based on survival and 1.3- to 2.8-fold based on biomass relative to a susceptible population. A subsequent field study where one of the populations originated confirmed that twenty percent of treated plants survived the labeled GA field-recommended rate. Screening with other herbicide site-of-action groups revealed that most populations showed reduced sensitivity to atrazine, glyphosate, and imazethapyr, surviving up to three times the field-recommended rates, and to a lesser extent, lactofen and fomesafen. Transcriptomic analysis of plants surviving GA revealed no resistance-associated mutations or differential transcript abundance in the plastidic and cytosolic isoforms of glutamine synthetase. Among the four suspected resistant populations, there were 182 genes differentially expressed relative to two susceptible populations. Different sets of genes were differentially expressed among the populations studied, with only one gene (upregulated relative to two susceptible populations) shared among all four. Many of the differentially expressed genes, including cytochrome P450s, glutathione S-transferases, glycosyltransferases, transporters, and transcriptional regulators, are commonly associated with metabolic resistance. Gene ontology enrichment analyses indicated significant overrepresentation of stress response, defense regulation, and secondary metabolism categories across the populations. Together, these findings provide evidence for the evolution of GA resistance in populations of A. tuberculatus in Illinois. While more in-depth studies are needed to fully characterize the underlying mechanisms, the consistent differential expression of metabolism-related genes and no indication of target-site mechanisms points to a potential metabolic basis for resistance.

Understanding how reduced-tillage practices influence weed community assembly is critical for designing ecologically sustainable organic cropping systems. We evaluated the effects on emerged weed biomass and seedbank dynamics of three cropping systems combining contrasting tillage regimes and cover crop strategies within an organic corn (Zea mays L.)–soybean [Glycine max (L.) Merr.]–spelt (Triticum spelta L.) rotation. Drawing from community assembly theory, we tested the roles of abiotic (soil disturbance), biotic (crop competition), and legacy filters (crop entry and cover crop history) across crop phases and spatial positions (interrow vs. intrarow). Our results show that weed community composition was shaped more by crop identity, spatial heterogeneity, and legacy effects than by tillage intensity alone. In soybean, the system with the lowest disturbance and a 14-mo undisturbed red clover (Trifolium pratense L.) cover crop legacy (IT/C–NT/S) selected for low-diversity communities dominated by giant foxtail (Setaria faberi Herrm.), particularly in intrarow zones. In contrast, in corn, spatial location explained more variation than cropping system, with intrarow communities again consistently dominated by S. faberi. Seedbank composition did not differ among systems but was significantly more diverse in the entry that had spelt in the last year of the rotation compared with the entry that had it in the first year, suggesting a strong filtering effect of the winter crop. Indicator species analysis further confirmed system-level filtering, with S. faberi strongly associated with low-disturbance soybean systems. These findings underscore the importance of considering within-field spatial heterogeneity and rotational legacy when designing organic weed management strategies and support the use of ecological filtering frameworks to understand weed community dynamics in complex organic systems.

A series of laboratory experiments was conducted to evaluate the germination ecology of buttongrass [Dactyloctenium radulans (R. Br.) P. Beauv.] for designing weed management practices in eastern Australia. Two populations (BG3 and BG4) were evaluated under varying temperature, light, salinity, water stress, residue cover, and burial depth conditions. Germination was completely inhibited at 15/5 C (alternating day/night temperature regime) but increased at high temperature regimes, reaching 90–92% at 30/20 C and remaining high (72–88%) at 35/25 C, indicating strong adaptation to warm climates. Both populations germinated well in light (12 h)/dark (12 h) conditions (87–93%), while BG3 showed a reduction (80%) in complete darkness (24 h) compared with light/dark conditions, suggesting weak positive photoblastic behaviour. Germination decreased progressively with increasing sodium chloride (NaCl) concentrations, with 50% inhibition at 40 mM NaCl, indicating moderate salt tolerance. Germination was reduced by 50% at osmotic potentials of -0.30 MPa and -0.25 MPa for BG3 and BG4 populations, respectively. Seedling emergence declined with increasing sorghum residue loads, dropping by >80% at >6 Mg ha-1, and was completely inhibited at 8 cm burial depth. These results demonstrate that D. radulans is a thermophilic, light-responsive, shallow-emerging grass capable of germinating under moderate salinity and water stress conditions, enabling persistence in semi-arid and reduced-tillage systems. High residue retention and deep burial of seeds (≥8 cm) could significantly suppress emergence, providing ecologically sustainable management options. Future studies should quantify population-level physiological variations and integrate temperature, moisture, and residue interactions into predictive emergence models to guide region-specific weed management under changing climatic conditions.

Clonality plays an important role in the proliferation of invasive species and, when coupled with loss of seed viability, can facilitate invasive success by reducing reliance on sexual reproduction and promoting spread of genetically identical individuals. Clonal invasions are advantageous for biological control strategies, as biological control agents may have a uniformed, damaging response to invasive populations with low genetic diversity. Agents sourced in the native range that are locally adapted to the same plant genotype that is invasive, may cause this response. Understanding the population genetics and invasion history of a species in the novel range is paramount to ensure effective biological control agents are introduced. Here we investigated the population genetics of pickerelweed (Pontederia cordata L.), a tristylous invasive macrophyte native to North and South America causing detrimental impacts in South Africa (SA). SA populations all have only one of three tristylous forms and produce no seeds. Inter Simple Sequence Repeats (ISSR) of P. cordata leaf samples from SA and from parts of the native range in the United States of America (USA) were used to determine population structure and potential source populations. Pontederia cordata has low genetic diversity within and amongst invasive populations in SA compared to native populations. This suggests no sexual reproduction and limited gene flow in SA, and only one introductory event. Invasive populations shared the closest genetic similarity with native samples from Virginia, USA, and although large parts of the indigenous distribution were not sampled, this close match suggests that the site may be a suitable area to source potential biological control agents. However, genetic sampling in other native areas should also be considered to confidently determine the origin of SA populations. This study corroborates other global findings of highly successful invasive species utilizing clonality, and consequently, resulting in invasive genotypes with low diversity.

Laser weed control is an emerging non-chemical technology made feasible by recent advances in artificial intelligence and automation. This research evaluated the response of four turf and weed species to varying levels and patterns of laser intensity to determine practical applications of laser weeding in turfgrass systems. Field experiments were conducted from July 2024 to March 2025 on research fairways in Blacksburg, VA, using a 10 W diode laser in spiral patterns with varying pattern-averaged energy densities (PAED). Two studies were implemented: one evaluated increasing energy intensity, and the other assessed combinations of line spacing, PAED, and number of passes in a factorial design. Line spacing significantly influenced weed control efficacy, with 4-mm spacing improving green cover reduction by up to 10% over denser patterns at the same PAED. Bermudagrass [Cynodon dactylon (L.) Pers.] recovered fully within 24 days post-treatment, while creeping bentgrass (Agrostis stolonifera L.) showed prolonged injury at higher intensities and wider spacings. These results demonstrate that laser weeding is feasible in turfgrass systems, especially with optimized energy and pattern configurations, and highlight the need for pattern customization to balance weed control with turfgrass safety.

Isoproturon is widely used to control Italian ryegrass [Lolium perenne (L.) ssp. multiflorum (L.) Husnot] in wheat fields across China. Here, we identified a highly resistant population (HR) from 87 populations collected from wheat fields, which showed 4.6-fold resistance to isoproturon compared to susceptible control (HS). DNA sequencing of the full-length psbA gene revealed no sequence differences between HR and HS plants. However, psbA expression in the HR population was significantly higher than in the HS population, both before and after isoproturon application. Transgenic assays confirmed that psbA gene overexpression in rice plants confers resistance to PSII inhibitors, including isoproturon. Under isoproturon application, the HR population also demonstrated elevated antioxidant enzyme activities and maintained higher chlorophyll and carotenoid levels. Furthermore, the HR population remained susceptible to pyroxsulam and pinoxaden, suggesting that these herbicides are practical alternatives for control. These findings indicate that psbA gene overexpression contributes to isoproturon resistance in L. perenne ssp. multiflorum, likely through the overproduction of the D1 protein to mitigate herbicide-induced PSII dysfunction. Our study provides the first confirmation and mechanistic explanation of isoproturon resistance in L. perenne ssp. multiflorum, revealing psbA gene overexpression as the key driver.

Annual bluegrass (Poa annua L.) is an extremely problematic weed in turfgrass, posing a significant challenge for turfgrass management. Injudicious use of herbicides for controlling this weed has led to resistance issues and environmental concerns. Site-specific weed control offers an opportunity to achieve effective weed control with less herbicide use, but it requires the development of a pipeline for weed detection and localization, and a path planning algorithm. To achieve this, unmanned aerial system (UAS) based RGB imagery of P. annua plants in bermudagrass turf was collected at different weed growth stages at two locations in Texas: Deer Park and College Station. A CNN (YOLO11) and a transfer (RTDETRD) model were evaluated for weed detection. The results showed that the YOLO11n model achieved the highest F1-score (0.64) and mAP@0.50 (0.68), while the RTDETRD-x model achieved the lowest F1-score (0.52) and mAP@0.50 (0.51). The geo-transformation function transforms image coordinates into a world coordinate system with centimeter-level accuracy (mean error =1.5 cm). However, the precision of the transformation depends on the quality of the orthophoto georeferencing. Additionally, the path planning algorithm showed a significant reduction (37.7%) in travel distance compared to the original weed-model-derived distance. The research highlighted the potential of UAS-based imagery for weed detection and localization in turfgrass. Further improvements are needed to enhance model performance by modifying the model architecture (e.g., input image size, hyperparameters) and evaluating its robustness across different weed growth stages and turfgrass species.

The academic training of professionals influences the evolution and future direction of scientific disciplines. However, the training background and demographic composition of weed science faculty have not been systematically characterized. To address this, we conducted an Internet-based survey of weed science faculty at universities in the United States of America (USA). This included the academic fields of the degrees these faculty had received, the institutions that granted these degrees, which USA state or country (if outside the USA) the degrees came from, the current academic rank of each faculty member, whether the faculty held leadership positions at their university, and the gender of each faculty member. We identified 223 faculty at 50 universities. They received their degrees from institutions in 24 countries and 39 USA states. Most of their BS degrees were in agronomy and crop science or plant science, physiology, and genetics, with few weed science and ecology degrees. Weed science and ecology representation increased at the MS level and became the most common doctoral training area. A plurality of the faculty were professors (48.9%), followed by assistant professors (28.7%), associate professors (19.7%), lecturers (0.9%) and unidentified rank (1.8%). Men made up 82.5% of the faculty with women at 17.5%. Men also held more of the leadership positions (84.4%) than women (15.6%). These findings provide the first comprehensive overview of the weed science academic workforce of the USA and establish a baseline for evaluating future trends in training pathways, disciplinary identity, workforce diversity, and potential continental or international comparisons.

Palmer amaranth (Amaranthus palmeri S. Watson) poses a significant threat to northeastern US crop production due to its rapid growth, prolific seed production, and evolving herbicide resistance. This study characterized the response of four A. palmeri populations from New York (NY) and New Jersey (NJ) to postemergence (POST) applications of atrazine, a photosystem II (PSII) inhibitor, and mesotrione, a hydroxyphenylpyruvate dioxygenase (HPPD) inhibitor. Dose-response bioassays revealed that two NY populations (NY-GEN and NY-STE) exhibited high-level atrazine resistance, 31- to 42-fold based on ED90 estimates, whereas NY-ORA and NJ-CMB populations remained susceptible. Target-site sequencing of the psbA gene revealed no mutations, indicating that resistance is conferred by a non-target-site mechanism. Metabolic assays demonstrated that resistant populations retained 20-21% less intact atrazine 48 h post-treatment compared to the susceptible reference, suggesting enhanced metabolism likely mediated by glutathione S-transferase enzymes. All populations were susceptible to mesotrione, with the field rate of 105 g ai ha-1 providing ≥94% control. Tank mixtures of atrazine plus mesotrione applied postemergence provided near-complete control (≥97% biomass reduction relative to nontreated checks) across the tested populations, including those resistant to atrazine alone, which is consistent with synergistic interactions between PSII and HPPD inhibitors. This study documents two new cases of atrazine-resistant A. palmeri in NY and shows that resistance is mediated by enhanced metabolism, consistent with findings from other states. These results have important implications for northeastern corn (Zea mays L.) production, where atrazine remains foundational to weed management. The sustained efficacy of atrazine-mesotrione combinations offers an immediate management option, but integrated strategies incorporating multiple herbicide sites of action and cultural practices are critical to prevent further resistance evolution.

Italian ryegrass [Lolium perenne (L.) ssp. multiflorum (Lam.) Husnot], a cool-season forage crop in temperate countries, is also a major weed problem in winter crops, especially wheat (Triticum aestivum L.). Understanding the molecular mechanisms underlying its adaptive traits is crucial for managing L. perenne ssp. multiflorum as both a crop and a weed species. Genome-wide association studies (GWAS) were performed using single nucleotide polymorphism (SNP) data from double-digest restriction site associated DNA (ddRAD) sequencing to assess the genetic diversity and identify the genetic region(s) associated with key adaptive traits, namely tillering ability, regrowth rate, and seed shattering in this species. A collection of 56 wild/weedy populations, 25 half-sib breeding lines, four commercial cultivars, and one reference sample each of L. perenne ssp. multiflorum, perennial ryegrass (Lolium perenne (L.), rigid ryegrass (Lolium rigidum Gaudin), and poison ryegrass (Lolium temulentum L.) obtained from the USDA-GRIN were used for the study. About 3,079 SNPs were used for principal component and marker-trait association analyses. In the principal component analysis, the half-sibs, cultivars, and wild populations clustered separately; however, a few wild populations were mixed with the half-sibs. Sequence annotation of the flanking sequences of significant SNPs identified in GWAS with the NCBI database revealed potential candidate genes underlying the traits, including Ethylene receptor2 promoting regrowth in common barley (Hordeum vulgare L.) and other species; an auxin-responsive protein SAUR36-like controlling tiller production in Tausch’s goatgrass (Aegilops tauschii Coss.) and river wheat (Triticum turgidum L.; syn. Triticum dicoccoides Koern. Ex. Schwinf.); and 4-coumarate-coenzyme A ligase for reduced seed shattering in L. perenne and L. rigidum. This information on marker-trait associations for these traits in L. perenne ssp. multiflorum will aid in manipulating the traits in crop breeding and weed management programs.

Weed-induced nutrient competition represents a major limitation on yield and quality in organic wheat cultivation. This study evaluated the effects of wide-range sowing on root-driven nutrient competition dynamics between wheat (Triticum aestivum L. Yongliang 4) and weeds. A two-year experiment (2019∼2020) in Bayannur, Inner Mongolia, compared three treatments: wide-range uniform sowing (W0), 7 cm wide-range sowing (W7), and conventional drilling sowing (CK). The study measured grain yield and protein content, root traits, and the dynamic changes in nutrient accumulation of organic wheat and field weeds, analyzing the nutrient competition levels and their responses to the different sowing methods. The two-year data demonstrated that both W0 and W7 treatments significantly enhanced grain yield in organic wheat compared to CK, with yield increments of 28.2% and 15.1% respectively. Compared to CK, the W0 treatment significantly improved root system development and nutrient uptake. Throughout various growth stages (at 60, 85, and 100 days after sowing, DAS), the average root length, surface area, volume, and weight density within the 0∼80 cm soil profile increased over 13.8%, 24.5%, 14.1%, and 19.2% respectively under W0 treatment. Concurrently, nitrogen (N), phosphorus (P), and potassium (K) uptake in wheat plants under W0 treatment showed enhancements over 34.6%, 39.5%, and 39.6% compared to CK. In contrast to the enhanced nutrient uptake in wheat, both experimental treatments significantly suppressed weed nutrient uptake. The W0 treatment reduced N, P, and K uptake in weeds by 55.9%, 57.9%, and 51.9% respectively, while W7 treatment decreased these parameters by 40.1%, 39.8%, and 40.2%. The wide-range sowing pattern particularly enhanced the nutrient competitiveness of organic wheat, with this competitive advantage becoming more pronounced during later growth stages. Statistical analyses revealed significant positive correlations between grain yield/protein content and root morphological parameters, as well as plant nutrient uptake. Conversely, significant negative correlations were observed between wheat productivity parameters and weed nutrient uptake, suggesting effective resource competition by the wheat plants under modified cultivation practices. In conclusion, wide-range sowing cultivation improves the nutrient competition ability of organic wheat through enhancing root traits, thereby suppressing weed access to nutrient resources and ultimately increasing both yield and grain quality of organic wheat.

Johnsongrass [Sorghum halepense (L.) Pers.] is a highly invasive, persistent, and problematic perennial weed in Australian cropping systems; however, its germination ecology has largely been inferred from studies conducted outside eastern Australia, where environmental conditions differ markedly. This limits accurate prediction of emergence timing and optimization of management strategies. The objectives of this study were to characterize seed dormancy mechanisms and to quantify the germination and emergence response of two populations of S. halepense from central Queensland to temperature, light, salinity, osmotic stress, and burial depth under controlled conditions. Seeds from both populations exhibited strong primary dormancy, which was partially alleviated by sodium hypochlorite immersion and more effectively by mechanical scarification using sandpaper, indicating that seed coat-related dormancy is the principal barrier to germination. Temperature significantly influenced germination, with no germination at 15/5 C and high germination (> 90%) at 25/15 C to 35/25 C under both light/dark and dark conditions, demonstrating that warm temperatures largely override light requirements. Germination declined steadily with increasing sodium chloride (NaCl) concentrations, and the NaCl concentration required to reduce maximum germination by 50% was approximately 173 mM. Moderate water stress −0.2 to −0.4 MPa had less germination in comparison to the control, while −0.8 MPa greatly inhibited germination (11%). Emergence was highest from shallow burial depths of 1 to 4 cm and declined sharply beyond 8 cm. These results demonstrate that S. halepense recruitment occurs in a range of environmental conditions; however, environmental stresses or deep soil burial may help manage this weed. This study provides regionally relevant information to enhance emergence prediction and inform integrated weed management strategies in eastern Australian cropping systems.

Palmer amaranth (Amaranthus palmeri S. Watson) is one of the most problematic weeds in U.S. agriculture, capable of rapidly adapting to environmental and management pressures. This study assessed temporal changes in glyphosate response in A. palmeri by comparing ED50 values, shikimic acid accumulation, and 14C-glyphosate absorption and translocation in four biotypes collected from two Georgia fields, Jones (J) and Little Jones (LJ), in 2008 and 2023. Glyphosate ED50 increased 9-fold (J08 vs. J23) and 25-fold (LJ08 vs. LJ23), indicating a marked reduction in glyphosate sensitivity between collection periods. Shikimic acid accumulation increased with glyphosate dose in all biotypes but remained substantially lower in biotypes collected in 2023, indicating reduced EPSPS inhibition. Radiolabeled assays revealed differences in early uptake, with populations collected in 2023 reaching near maximum absorption more rapidly, as reflected by shorter times to 95 percent absorption (A95), although total absorption continued to increase across all biotypes through 48 hours after treatment. Translocation patterns varied only slightly among biotypes, suggesting that changes in glyphosate response are associated more closely with altered uptake kinetics and EPSPS related mechanisms than with major reductions in systemic movement. These results demonstrate a temporal shift in glyphosate response in Georgia A. palmeri populations and highlight the importance of integrating kinetic analyses with traditional resistance metrics.

Planting green (PG), the practice of planting the cash crop into a living cover crop (CC), offers opportunities to maximize CC biomass and weed suppression. The objectives of this study were to evaluate the effects of cereal rye (Secale cereale L.) termination timing and herbicide programs under PG management on cereal rye biomass, Palmer amaranth (Amaranthus palmeri S. Watson) suppression and seed production, corn (Zea mays L.) yield, and economic returns. Field experiments were conducted during 2023 to 2025 under irrigated conditions in south-central Nebraska. The study used a split-plot design, a no–cover crop (NCC) and five cereal rye CC termination timings (at planting, emergence, V1, V2, and V3 corn growth stages) as the main plot factor and four herbicide programs (nontreated, preemergence-only, postemergence-only, and preemergence followed by postemergence [PP]) herbicide as subplot factors. Delaying cereal rye termination from corn planting up to V3 corn growth stage increased cereal rye biomass from 5,992 to 10,888 kg ha−1 in 2024 and from 2,941 to 7,007 kg ha−1 in 2025. Cereal rye terminated at V2 or V3 corn growth stage reduced A. palmeri density, biomass, and seed production by >99% compared with the NCC. Following high biomass conditions, cereal rye provided comparable A. palmeri suppression to herbicide-based programs, and the additional herbicide use offered limited benefit. In contrast, following low-cereal rye biomass conditions (<6,000 kg ha−1), herbicide inclusion remained essential to achieve effective A. palmeri control and minimizing seed production. Corn yield was not affected by delayed cereal rye termination (ranging from 13,110 to 15,660 kg ha−1). Economic analysis indicated that integrating cereal rye CC with reduced herbicide programs (preemergence-only or postemergence-only) maintained profitability ($2,064 to $2,364 ha−1) comparable to the NCC system with PP herbicide program ($2,353 to $2,401 ha−1).

Corn poppy (Papaver rhoeas L.) is a problematic weed in cereal farms in Ireland, necessitating continuous herbicide use to protect crop yields. In 2022, poor control with acetolactate synthase (ALS) inhibitors and auxin-mimic herbicides was reported by growers/advisors in two resistance-suspect populations, namely PAPRH-R1 and PAPRH-R2. In this study, we quantified their resistance to both herbicide modes of action and investigated the underlying mechanisms. ALS inhibitor dose–response experiments revealed that both populations had ED50 and GR50 resistance indices (RIs) above 120 to thifensulfuron + tribenuron, mesosulfuron + iodosulfuron + amidosulfuron, and metsulfuron, and values of 4 to 13 to florasulam + pyroxsulam. Results of 2,4-D dose–response assays revealed higher resistance in PAPRH-R2 (ED50 and GR50 RI > 9.1) than PAPRH-R1 (ED50 and GR50 RI > 3.4). ALS gene sequencing detected Pro-197 mutations in all sequenced plants from both resistant populations. Pretreatment with piperonyl butoxide (PBO, a cytochrome P450 inhibitor) reversed 2,4-D resistance with GR50, the more sensitive response parameter, decreasing from 680.8 to 84.9 g ha−1 in PAPRH-R1 and from 2,508.9 to 456.8 g ha−1 in PAPRH-R2, both well below the recommended label rate of 1,000 g ha−1. The 14C-2,4-D assays ruled out reduced absorption or translocation as resistance mechanisms. Sensitivity screening further revealed incomplete control with other postemergence foliar herbicides tested at half and full recommended label rates, except for fluroxypyr + halauxifen, which provided complete control of PAPRH-R1 at the full rate, and glyphosate, which provided complete control of PAPRH-R1 and PAPRH-R2 at both rates. This is the first report of multiple resistance in P. rhoeas in Ireland involving ALS target-site mutations and likely P450-mediated 2,4-D metabolism. As cultural/nonchemical control of broadleaf species is difficult, the continued availability of preemergence or autumn residual herbicides, together with effective auxin mimics and stewardship practices, will remain essential for managing these species, including P. rhoeas, in cereal crops.

Italian ryegrass [Lolium perenne ssp. multiflorum (Lam.) Husnot] (referred to as L. multiflorum hereafter) is one of the most problematic grass weeds infesting agronomic and specialty crops across the United States. In 2023 to 2025, inadequate control of L. multiflorum populations (NY_R1, NY_R2, and NY_R3) with glyphosate was reported in Livingston, Ontario, and Genesee counties, New York. This research aimed to (1) confirm and quantify glyphosate resistance in these suspected glyphosate-resistant (GR) populations, (2) evaluate the efficacy of alternative postemergence herbicides, and (3) determine whether EPSPS gene amplification confers glyphosate resistance. A known glyphosate-susceptible (GS) population (AR_S) from Arkansas was included for comparison. Glyphosate dose–response assays indicated that NY_R1, NY_R2, and NY_R3 populations were 13-, 4-, and 5-fold resistant, respectively, relative to the AR_S population. Alternative postemergence herbicides, including clethodim, glufosinate, paraquat, and pinoxaden, provided 96% to 97% control and reduced shoot dry weight by 91% to 97% at 21 d after treatment (DAT). In contrast, nicosulfuron provided reduced control (63% to 74%) and limited biomass reduction (51% to 56%), suggesting possible resistance to acetolactate synthase (ALS)-inhibiting herbicides in three tested populations. Quantitative PCR analysis revealed that NY_R1 and NY_R3 had approximately 30-fold higher EPSPS gene copy numbers than AR_S, indicating gene amplification as a mechanism of glyphosate resistance. This study confirms the first case of GR L. multiflorum associated with EPSPS gene amplification in New York, underscoring the need for integrated, diversified weed management strategies to mitigate its spread.

Effective weed management is critical to the long-term productivity of organic grain cropping systems. The Cornell Organic Cropping Systems Experiment was initiated in 2005 at the Musgrave Research Farm in Aurora, NY, to compare four organic cropping systems that differed primarily in intensity of mechanical weed management and soil nutrient inputs. A 3-yr rotation of corn (Zea mays L.), soybean [Glycine max (L.) Merr.], and spelt (Triticum spelta L.)/red clover (Trifolium pratense L.) was grown in all systems. The four systems were characterized by High Fertility (red clover green manure, composted poultry manure, and commercial organic fertilizer to reach recommended fertility levels), Low Fertility (no fertility inputs other than the red clover and starter fertilizer for corn), Enhanced Weed Management (fertility management as in Low Fertility with additional tillage and cultivation and a higher spelt seeding density), and Reduced Tillage (primarily ridge tillage with different green manure crops). The experiment included two crop rotation entry points, enabling two of the three crops in the rotation to be grown every year. Results from the first two rotation cycles show that, in most cases, weed abundance and diversity increased during the transition to organic production, especially in the Reduced Tillage system. Perennial weeds increased in corn and soybean in the Reduced Tillage system in the second rotation cycle, which contributed to its poor performance relative to the three other systems. Our results suggest that increased soil disturbance, including tillage and cultivation in corn and soybean, plays an important role in reducing weed populations, whereas high fertility levels may exacerbate weed problems. These findings underscore the importance of balancing weed and nutrient management in enabling sustainable organic grain crop production.

Rice (Oryza sativa L.) agriculture of the southern United States is plagued by strong biotic competition with several species in the Echinochloa genus. Despite clear genomic differences between barnyardgrass [Echinochloa crus-galli (L.) P. Beauv.] and junglerice [Echinochloa colona (L.) Link], the two major Echinochloa agricultural weeds are nearly indistinguishable phenotypically. This inability to reliably differentiate the species has led farmers to treat the group as a single species, often resulting in ineffective weed control efforts. In this study, we first develop a simple chloroplast-anchored PCR-based restriction enzyme assay to differentiate between E. colona and the other Echinochloa species of agricultural concern. Applying this assay, we identify a strong bias toward E. colona in 2024 rice field collections from eastern Arkansas. Finally, we evaluate anecdotal reports of interspecific hybridization between the species and find no evidence. Despite the drawbacks of the maternally inherited nature of the chloroplast genome, the availability of this species determinant assay will help USDA and academia extension agents and stakeholders to make educated, species-specific decisions about precision chemical weed control and field management.

Delaying cover crop termination until planting (i.e., planting green) in no-till production systems is likely to mediate the fate of herbicides that provide soil-residual activity. There is currently limited knowledge of how the interaction between physiochemical properties of cover crop residues and sorption properties of herbicides influence the wash-off potential of residual herbicides from cover crop residues in a planting green scenario. We conducted field- and laboratory-based experiments using herbicide wash-off assay methods to evaluate the interaction between lignin (%) of cereal rye (Secale cereale L.) and herbicide lipophilicity (Kow) on wash-off potential across herbicide application timings. We contrasted herbicides with intermediate lipophilicity (atrazine, pyroxasulfone, and S-metolachlor) to less lipophilic (mesotrione) and highly lipophilic (pendimethalin) herbicides. Wash-off was greater for atrazine and pyroxasulfone than for mesotrione and S-metolachlor when applied into living cereal rye. Pendimethalin had the least wash-off potential. When pendimethalin was applied into fresh to aged cereal rye residues (0 to 84 d after termination), wash-off was below the detection threshold. Wash-off of mesotrione, pyroxasulfone, and atrazine declined as lignin (%) in cereal rye residues increased, whereas a positive relationship between S-metolachlor recovery and lignin (%) was observed. Results of our study partially support the hypotheses that (1) herbicide lipophilicity, measured via log Kow values, can be a useful indicator of wash-off potential among residual herbicides used in cover crop systems; and (2) wash-off potential declines as cover crop residues age within herbicide application windows.