The rice (Oryza sativa L.)–wheat (Triticum aestivum L.) cropping system (RWCS), recognized as the world’s prime agricultural system, plays a pivotal role in global food security by providing employment for millions and ensuring a steady income, thereby serving as a cornerstone for farmers’ livelihoods and attracting numerous investors. However, the sustainability and efficiency of this critical system face momentous threats due to climate change, which affects both the quantity and quality of wheat and rice crops. Currently, the growth frequency of the RWCS has declined, principally due to evolving challenges such as weed infestation, delayed wheat sowing after rice harvest, soil salinity, and the prevalence of various diseases. Among these challenges, weeds pose a considerable threat to the cultivation of both rice and wheat. Seed germination, a crucial stage in the plant life cycle, is influenced by various factors, including dormancy, temperature, moisture, oxygen, and light. A comprehensive understanding of weed ecology is essential for identifying vulnerabilities that can be targeted for improved weed management. Population-based threshold models, including hydro-time and thermal time, provide insights into germination patterns, contributing to the overall fitness of weed species. The ability to predict species’ responses to climate change is paramount, and these models are effective in comprehending and controlling weed emergence behavior across diverse environments. Hence, this review paper emphasizes the reevaluation of current weed management practices, focusing on investigating ecologically sustainable approaches for efficient weed control.

Wide diversity in plant adaptive traits, such as seed size and dormancy, is generally linked to the rapid spread, invasiveness, and adaptative potential of a weed species. Italian ryegrass [Lolium perenne L. ssp. multiflorum (Lam.) Husnot] is a significant weed species in winter crops such as wheat (Triticum aestivum L.) and summer crops such as corn (Zea mays L.), soybean [Glycine max (L.) Merr.], and peanut (Arachis hypogaea L.) in Alabama. In this study, diversity in seed morpho-physiological traits—such as seed length, awn length, seedling length, 100-seed weight, and seed dormancy—was assessed in 65 L. perenne ssp. multiflorum populations collected from Alabama in 2023. Significant diversity was observed among the populations for 100-seed weight (61.8 to 295.8 mg), seed length (3.5 to 6.43 mm), awn length (0 to 7 mm), and seedling length (0.5 to 38.6 cm). Germination speed was significantly lower in the populations with high initial seed dormancy (>30%) compared with medium (15% to 30%) and low dormancy groups (<15%) at 0 and 3 mo after harvesting. Additionally, the relationship between herbicide-resistance status and seed morpho-physiological traits in these populations was explored. A significant positive association was observed between seed dormancy and the number of survivors following glyphosate (P < 0.01) and clethodim (P < 0.01) treatments. The observed diversity in morpho-physiological traits could be the reason for enhanced adaptability of L. perenne ssp. multiflorum, and its correlation with herbicide resistance indicates directional selection or coexistence of specific seed morpho-physiological traits with herbicide resistance under the repeated use of similar modes of action.

American sloughgrass [Beckmannia syzigachne (Steud.) Fernald] is a troublesome weed in wheat (Triticum aestivum L.). We tested the germination of B. syzigachne seeds under different temperatures in growth chambers (12-h dark/12-h light, 12,000 lx), simulating temperatures during the winter wheat sowing periods: early (25/15 °C), standard (20/10 °C), late (15/5 °C), and very late (5/0 °C). We also tested the accumulated temperatures required for seedling growth to the 2- to 5-leaf stages, using 225 populations collected from wheat fields in eastern China. The average 1,000-seed weight of the 225 populations was 1.2 ± 0.01 g. Overall, the populations tested did not show seed germination after 21 d of treatment (DAT) at 5/0 °C or constant 30 °C. At 14 DAT with 25/15, 20/10, and 15/5 °C, the mean germination rates were 85.4%, 6.4%, and 0.1%, respectively. These rates increased to 99.9%, 58.6%, and 21.7% at 21 DAT. Populations collected from lower-latitude regions germinated significantly faster (P < 0.05) under optimal conditions. Accumulated temperatures required for growing the second, third, fourth, and fifth leaves were 139.0 ± 1.0, 127.8 ± 1.0, 115.6 ± 1.0, and 98.9 ± 0.7 °C, which showed a significant decreasing trend. The narrower optimal temperature range for B. syzigachne seed germination and higher thermal requirements for early seedling growth constrain its distribution, while the heterogeneous seed germination facilitates its infestations in wheat-planting areas in eastern China.

Weed pressure threatens lentil (Lens culinaris Medik.) yields, with metribuzin offering control but risking crop injury. This study used hydroponics to screen metribuzin tolerance in lentils, determining the lethal dose causing 50% mortality (LD50) for lentil cultivar ‘CDC Greenstar’ and profiling metabolites in three genotypes, ‘VIR421’ (susceptible), CDC Greenstar (tolerant), and ‘NZ2022’ (medium tolerant), via liquid chromatography–mass spectrometry (LC-MS). CDC Greenstar plants in a hydroponic deep-water culture system were exposed to metribuzin doses (0.17, 0.25, 0.51, and 2.05 g ai ha⁻1, plus a control) selected based on preliminary trials that identified the effective range for LD50 estimation in hydroponics, where herbicide bioavailability is higher than in soil due to direct root exposure and absence of soil adsorption. These doses are substantially lower than the recommended field application rate of 205 g ha⁻1 as a preemergence treatment for lentils to account for the amplified effects in hydroponics for 24 h, with biomass reductions assessed over 21 d. The LD50 was 0.4407 g ha⁻1 (R2 = 0.94), with dose strongly reducing shoot/root growth (r = −0.92 to −0.99). Untargeted LC-MS identified seven metabolites in CDC Greenstar and VIR421, including desamino-metribuzin (DA) and conjugates, while targeted LC-MS tracked metribuzin, DA, and desamino-diketo-metribuzin (DADK) over 12 d. VIR421 had higher metribuzin levels (105.70 ng g−1 at dry weight at 12 h) compared with CDC Greenstar and NZ2022, which rapidly metabolized metribuzin to DA (58 and 50.41 ng g−1 dry weight at 2 d), with NZ2022 showing further metabolism by 4 d. DA dominated 59- to 167-fold over DADK, suggesting a primary detoxification pathway. Hydroponics enabled precise tolerance screening, revealing genotype-specific metabolism critical for breeding metribuzin-tolerant lentils and thus enhancing weed management strategies.

Pollinators are susceptible to insecticide residues when foraging on weedy flowers in turfgrass systems. Deterrent practices may mitigate this risk by reducing pollinator visits; however, their effectiveness in limiting contact exposure of pollinators has not been thoroughly evaluated. Two trials were conducted using a randomized complete block design with three temporal blocks to assess the effectiveness of deterrent practices in preventing contact exposure of actively trapped honey bees (Apis mellifera) and passively trapped insects to fluorescent powder–treated white clover (Trifolium repens L.) inflorescences in turfgrass. Deterrent treatments included mowing the same morning before fluorescent powder application; spraying with a premix of 2,4-D, MCPP, and dicamba 2 d before powder treatment; or no deterrent before powder application. Fluorescent powder was extracted from 1,440 honey bee specimens collected by active trapping at 4 and 28 h after treatment. Mowing and synthetic auxin herbicide pretreatment reduced the number of fluorescent powder–exposed honey bees by at least 75% and 93%, respectively. Among exposed honey bees, mowing and herbicide treatments reduced powder concentration by at least 75% and 90%, respectively. Honey bee visitation was positively correlated with T. repens inflorescence density, explaining 81% of visitation variability. Mowing transiently decreased T. repens floral density by 85%, but recovered by 7 d, while herbicides resulted in complete loss of floral resources by 7 d. Blue vane traps captured 1,117 bees from 23 species, of which greater than 96% were native, while yellow sticky cards collected 384 insects from the Lepidoptera, Diptera, and Coleoptera orders. Despite differences in honey bee exposure, deterrent treatments did not affect the exposure of passively trapped pollinators to fluorescent powder, likely due to strong visual attraction of traps. Results suggest that mowing and synthetic auxin herbicides effectively deter honey bees from T. repens inflorescences, reducing their exposure risk.

Improving herbicide efficacy under drought stress is essential for improving weed management and limiting the associated challenges. Leaf water content (LWC), a vital ecophysiological trait, can be used to indicate drought stress and improve herbicide efficacy. To investigate how water stress–induced changes in LWC affect glyphosate efficacy across diverse weed types, the broadleaf weed Santa Maria feverfew (Parthenium hysterophorus L.) and the narrow-leaf giant foxtail (Setaria faberi Herrm.) were selected. A controlled greenhouse study was conducted with two treatment factors including three moisture levels (well watered at 100% WHC, moderate drought at 75% WHC, and severe drought at 50% WHC) and glyphosate doses (0, 180, 360, 540, 720, and 900 g ae ha⁻¹). Drought stress significantly reduced LWC and stomatal conductance in both species; while the reduction in LWC was more pronounced in P. hysterophorus (26%) than in S. faberi (23%), the reduction in stomatal conductance was severe and similar for both species (82% and 83%, respectively). Severe drought stress drastically reduced shikimic acid concentration (41% to 59%) in both species. Severe drought stress significantly reduced glyphosate efficacy, suppressing mortality by up to 63% and biomass reduction up to 58%. Shikimic acid concentration and weed mortality both showed a strong positive correlation with change in LWC under all tested water-stress levels. Glyphosate applications when LWC falls below 70% resulted in poor weed control at recommended field rates. Therefore, LWC can be used as a real-time predictive biomarker to monitor drought stress, schedule irrigation before glyphosate application, optimize the dose, and ultimately improve its efficacy.

Bentazon, a photosystem II–inhibiting postemergence herbicide, has been used in corn (Zea mays L.), soybean, wheat (Triticum aestivum L.), and vegetables to manage common lambsquarters (Chenopodium album L.), although growers have reported reduced efficacy across the country. The aim of this study was to describe the sensitivity response of C. album to bentazon and identify whether reported escapes could be considered to be cases of herbicide resistance evolution. We evaluated C. album populations collected from lima and snap bean (Phaseolus vulgaris L.) fields across Delaware, Illinois, Minnesota, New York, and Oregon. Dose–response experiments with 25 populations were conducted to create a reference response to bentazon, using rates that ranged from 0 to 8,406 g ai ha−1. Injury ratings and biomass were assessed at 28 d after herbicide application, and the herbicide rates required to reduce growth by 50% (I50 or GR50) and 80% (I80 or GR80) were calculated. Results indicated C. album responses to bentazon varied within and across states. Across all populations studied, the GR50 for biomass reduction ranged from 159 to 816 g ha−1, and GR80 from 230 to 1,944 g ha−1 with populations from Oregon exhibiting the highest average GR50, followed by those from New York, the Northcentral states, and Delaware. Based on our criteria that the injury rating- or biomass-based resistance index (ratio between I50 or GR50 of the suspected resistant and a local selected susceptible population) had to be at least 2, and the I80 or GR80 should be greater than the labeled field rate, one population from New York (NY6) and one from Oregon (OR29) were considered to be resistant. This research underscores the wide variation in C. album response to bentazon across the United States and the importance of herbicide resistance diagnostic strategies that account for local population variation, and highlights the increasing challenge of C. album management in specialty crops.

Cover crops (CCs) are widely promoted for their multifunctional roles in sustainable agriculture, including improving soil health, enhancing crop productivity, and suppressing weeds. This meta-analysis quantitatively assessed the effects of CCs on three key outcomes: soil organic carbon (SOC), successor crop yield, and weed biomass, based on data from multiple independent studies. Weighted random-effects models and log response ratios (lnRR) were used to synthesize results. CCs significantly increased SOC (mean lnRR = 0.390), corresponding to an estimated 47.7% gain compared with controls, although substantial heterogeneity was observed (I2 = 97%), indicating context-dependent responses across systems. Successor crop yields showed an overall neutral response (mean lnRR = 0.052), with high between-study variability (I² = 90.5%), suggesting that positive or negative outcomes depend on site-specific factors. Weed biomass was consistently reduced across all studies (mean lnRR = −1.759), corresponding to an average 82.8% suppression, although variability remained high (I² = 99.2%). Complementary economic analysis indicated that while CCs involve initial establishment costs (∼US$150 ha−1), these are often offset by savings in agrochemical use, improved weed and fertility management, and long-term gains in land value. Altogether, the results highlight the potential of CCs as a sustainable agronomic practice, offering multiple ecosystem services and economic co-benefits. Optimizing species selection, management timing, and system integration will be key to maximizing outcomes under diverse agronomic conditions.

Common ragweed (Ambrosia artemisiifolia L.) is a globally distributed, difficult to control weed that can cause severe crop yield losses if not properly managed. Clopyralid is a synthetic auxin herbicide widely used to control A. artemisiifolia and other Asteraceae weeds. In 2016, a highly clopyralid-resistant A. artemisiifolia population, which we call AMBEL-40, was reported on a Michigan Christmas tree farm. We investigated the inheritance and potential clopyralid resistance mechanisms in this population using greenhouse dose–response assays; test crosses with a susceptible line—AMBEL-39; and RNA-seq. The ED50 values for AMBEL-40 and AMBEL-39 were 2,110.8 and 74.5 g ha−1, respectively; therefore, the resistant/susceptible ratio is 28.3. Dose–response results with triclopyr, fluoxypyr, 2,4-D, or dicamba demonstrate no multiple or cross-resistance in AMBEL-40. AMBEL-40 and AMBEL-39 crossed F1 generations (M3F1, M3F2, and M1F1) showed increased resistance compared with AMBEL-39, with ED50 values of 1,379.2, 1,134.0, and 542.5 g ha−1. Chi-square tests of three sib-mated F1 to generate F2 generations rejected a single-gene 1:3 model and supported a two-gene 3:13 segregation, consistent with multigenic inheritance. We identified 23 Aux/IAA transcripts containing the degron (IAA protein subdomain) sequence in the published A. artemisiifolia genome; of these, three contained polymorphisms in our RNA-seq data, but none consistently co-segregated with resistance. Differential expression analysis identified 70 genes with 39 upregulated and 31 downregulated in AMBEL-40, including candidates in auxin/ethylene signaling, metabolism, cuticular wax biosynthesis, and stress modulation, supporting a non–target site resistance mechanism. Together, these results indicate that clopyralid resistance in A. artemisiifolia is recessive and multigenic, with potentially altered signaling, metabolism, and uptake as a mechanism of resistance rather than a single Aux/IAA degron mutation.