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.

The root parasitic weed branched broomrape [Phelipanche ramosa (L.) Pomel] spends most of its life cycle underground, complicating early detection and control. A predictive model based on growing degree days (GDD) can improve management by anticipating key developmental stages. This study aimed to characterize P. ramosa phenology and develop a thermal time model to inform more effective control strategies. Two greenhouse experiments using rhizotrons were conducted over 2 yr (2021 to 2022), along with a complementary pot experiment in 2022 at Davis, CA. The P. ramosa development was classified into four phenological stages: attachment, elongation, emergence, and full flowering. We recorded the thermal timing (GDD accumulation from transplanting) and number of individuals at each phenological stage and modeled the development dynamics using an inverse Weibull function. Of the 255 P. ramosa attachments recorded across two rhizotron runs, 87% advanced to elongation, 63% reached emergence, and only 49% successfully developed to full flowering. Model estimates indicated that 5% of attachments occurred at 299 GDD and 95% by 730 GDD, marking a critical control window. After the initial attachment, on average, it took about 85 GDD for an attachment to initiate the elongation process, and 385 and 815 GDD to reach 5% and 95% elongation, respectively. Emergence followed, with 5% to 95% occurring from 520 to 1,100 GDD. Full flowering occurred roughly 181 GDD after emergence, spanning 700 (5%) to 1,280 (95%) GDD after transplanting. Model validation using data from related field experiments conducted in 2022 and 2023 in a P. ramosa–infested tomato (Solanum lycopersicum L.) field in Yolo County, CA, confirmed the model’s accuracy in predicting full flowering with root mean-square error (RMSE) of 142 GDD. This thermal time model offers a valuable decision support tool to optimize the timing of P. ramosa management, particularly in-season soil-applied herbicide programs, in tomato cropping systems.

Every year agriculture uses 2 million tonnes of plastic mulch in the form of polyethylene (i.e., “PE mulch”) to grow the world’s food. Plastic mulch is a key tool for growers to suppress weeds, improve crop microclimates, increase yields, mitigate erosion, and potentially enhance crop quality. However, plastic mulch use comes at a major environmental cost due to poor end-of-life outcomes. Hydromulch (also known as “hydramulch” or “hydro-mulch”) is an alternative, sprayable, soil-biodegradable mulch technology made from biobased feedstocks that can be formulated to be acceptable in certified organic agriculture in the United States and Canada. Paper-based hydromulches are generally made from some combination of recycled cellulose fiber, water, tackifier or other binding agents, and sometimes filler derived from various agricultural residues or waste products. The objective of this review is to provide a historical overview of hydromulch, highlight key findings from previous hydromulch research, and provide recommendations to advance the use of hydromulch as a biobased, soil-biodegradable alternative to plastic mulches in specialty crop agriculture. Feedstock and application costs are still major barriers for commercialization and may be mitigated by further research, including the creation of hydromulch formulations that utilize agricultural residues without compromising the physical properties of the mulch layer. Overall, this literature review indicates that hydromulch is a promising technology, but also one in need of further research to be viable across a broad spectrum of cropping systems and environments.

This systematic review evaluated studies published between 1980 and 2025 on the chemical control of smut grass [Sporobolus indicus (L.) R. Br.] in the Americas, with a focus on pastures. After 446 publications were screened, 13 peer-reviewed articles met the inclusion criteria. Most studies were conducted in the subtropical United States, particularly in Florida, on bahiagrass (Paspalum notatum Flueggé) pastures, with only one study carried out in Brazil. The most frequently reported herbicide was hexazinone, present in more than 80% of the studies, applied either alone or in combination with mechanical methods or fertilization. Consistent results indicated control efficacy above 85%, especially at doses ≥0.84 kg ha⁻1 and when applied during summer. Selectivity for use in bahiagrass was considered satisfactory despite temporary phytotoxic symptoms. Integrated strategies, such as herbicide applications combined with nitrogen fertilization, showed potential to restore forage dominance and reduce reinfestation. Other herbicides, such as glyphosate, indaziflam, imazapic, mesotrione, and triazines, were less frequently investigated. Indaziflam, applied preemergence, caused a significant reduction in the seedbank, showing promise for preventive management, given the high dormancy and longevity of S. indicus seeds. The integration of chemical and mechanical control produced variable outcomes: in some cases, mowing before application reduced efficacy, whereas in others, when associated with strategies to remove growing points and subsequent herbicide application, it enhanced control. The scarcity of studies under Brazilian and other tropical or subtropical conditions limits the understanding of this species’ adaptation and the efficiency of management methods across different edaphoclimatic contexts. Expanding research in these regions is crucial for developing effective and sustainable management strategies.

Khasi nightshade (Solanum khasianum C.B. Clarke) is a perennial poisonous weed in tropical and subtropical regions that seriously threatens the development of grasslands. For a high-risk invasive weed, a comprehensive understanding of its seed germination characteristics is important for predicting its spread and developing effective management strategies. However, the impact of various abiotic factors on the germination of S. khasianum is not clear. This study first explored the effects of temperature, light, pH, osmotic stress, salt stress, high-temperature pretreatment, and burial depth on the germination of S. khasianum. Seeds germinated at constant temperature of 30, 33, 35, and 38 C, and the germination rate (GR) ranged from 10% to 94%. The optimum germination temperature was 35 C, while germination was completely inhibited at 25 or 40 C. The germination of S. khasianum was greatly promoted by alternating light and darkness (16/8, 12/12, 8/16 h), but was not sensitive to the time change of photoperiod. The GRs were more than 70% in the pH range of 4 to 10, and a strongly acidic environment was more suitable for germination. The GR gradually decreased with the osmotic potential from 0 to −0.2 MPa, and no germination occurred at −0.4 MPa. Accordingly, germination was also low in sodium chloride (NaCl) solution with concentrations higher than 60 mM. Seeds of S. khasianum were not tolerant to high temperature; GR decreased significantly after exposure to 40 C for 5 min, and it decreased to 3% at 120 C. The emergence rate was the highest (93%) when the seeds were buried on the soil surface, while seedlings hardly appeared when the burial depth was more than 2 cm. This study revealed the possible adaptive mechanism of invasive S. khasianum and will contribute to the effective prediction of its spread and management in grasslands.

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.

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.

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.

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).

Object detection models, such as those in the YOLO family, are generally effective at identifying individual weeds, but their performance can be limited by occlusion of target structures in high-density scenes. These models are typically trained on images with low weed densities, where individual plants are clearly visible and easy to annotate, yet they are used in field conditions where areas of high density and dense vegetation may occur. Greenhouse experiments were conducted at the University of Florida, Wimauma, FL, to evaluate how purple nutsedge (Cyperus rotundus L.) density impacts the performance of a YOLOv8 model. A greenhouse density test dataset was developed by collecting 480 images of 12 densities ranging from 7 to 331 plants m−2, at transplant and at 3, 6, 10, and 17 d after transplanting. An independent dataset of 2,221 field and greenhouse images was used for the training of a YOLOv8 extra-large model to detect C. rotundus. A logistic sigmoidal model was fit to evaluate the F1 score as a function of increasing C. rotundus density at each data-collection time point. The F1 score showed sigmoidal relationships with density at all time points, exceeding 0.9 at low densities but dropping sharply to near 0 at the highest density and later time points. Performance decline was primarily driven by increased false negatives as density and occlusion increased, with minimal contribution from false positives, except at the highest densities. Density thresholds for optimal performance (F1 ≥ 0.90) decreased from 157 to 86 plants m−2 as canopy coverage increased, while marginal performance (F1 = 0.50) dropped from 322 to 140 plants m−2. Our findings suggest that object detection models for C. rotundus are strongly influenced by increased occlusion and morphological changes resulting from greater plant proximity and canopy coverage in high-density scenes.