Abstract Seed position on the mother plant, time of seed germination, and soil moisture can affect life-history characteristics of annual plants. However, most studies considered only one level of seed position, and how seed position combined with emergence season and watering regime affect life history traits of annual invasive plants is not clear. In this study, seeds in different positions within and between diaspores at different positions in compound spikes of the invasive diaspore heteromorphic annual grass Tausch’s goatgrass ( Aegilops tauschii Coss.) sown under different watering conditions and life-history traits were monitored. Seeds of A. tauschii germinated in autumn and in spring under both natural and increased soil moisture. Autumn-germinated plants were larger but allocated lower proportions of resources to reproductive organs than spring-germinated plants. Regardless of emergence season and soil watering regime, A. tauschii exhibited two levels of seed position effects on life-history traits. For distal diaspores/seeds, vegetative growth stage was longer and seedling emergence percentages, plant height, number of diaspores per tiller, and vegetative allocation were higher, while reproductive growth stage was shorter, and seedling survival percentages, number of tillers per plant, number of seeds per diaspore, and reproductive allocation were lower than for basal diaspores/seeds. Thus, in A. tauschii , distal diaspores/seeds represent a “high-risk” strategy and basal ones a “low-risk” strategy. This apparent “bet-hedging” strategy likely increases survival and geographic/habitat expansion of A. tauschii and also may contribute to its invasiveness.
Abstract Palmer amaranth ( Amaranthus palmeri S. Watson) is among the most economically damaging weeds in the United States and has evolved resistance to numerous herbicides, including glyphosate. This fast-growing species has expanded its range into different regions, including New York State, where glyphosate-resistant (GR) populations are now found. We evaluated how temperature modifies two components of weed risk, sensitivity to glyphosate and competitiveness against corn ( Zea mays L.), under growth chamber conditions. First, we performed a dose–response study testing glyphosate efficacy for a GR A. palmeri biotype from New York State and a glyphosate-susceptible (GS) biotype from Nebraska. Tests were conducted at low (25/15 C), medium (30/20 C), and high (35/25 C) day/night temperatures. The nontreated GS biotype produced greater biomass at low versus high temperatures. This biotype was highly sensitive to glyphosate across all temperatures. In contrast, biomass of the nontreated GR biotype did not vary with temperature. This biotype was less sensitive to glyphosate across all temperatures. Our second study tested whether temperature modifies the impacts of A. palmeri on corn biomass at four planting densities (zero, one, two, or four A. palmeri with one corn plant). We used the same three temperature regimes and the same two A. palmeri biotypes as the dose–response study. There was no evidence that the biotypes, at any planting density, were more competitive with corn under elevated temperatures. In fact, the biomass of A. palmeri decreased with increasing temperatures while corn biomass did not vary. In the competition study, the GS biotype from Nebraska had higher biomass than the GR biotype from New York. Overall, these results do not support the hypothesis that increasing temperatures would exacerbate the risk posed by the tested A. palmeri biotypes in corn. Instead, these two A. palmeri biotypes may be highly problematic under temperatures already occurring in New York State.
Abstract Crystalline ice plant [ Cryophytum crystallinum (L.) N.E. Br.] is a succulent plant indigenous to South Africa and is a highly invasive weed in North America. There are currently three weevil species from the native range that show promise as potential biological control agents for these invasive populations. The present study used a ddRADseq population genetic technique to match the invasive populations in North America to their source of origin to prioritize survey areas where the best-matched agent genotypes are likely to occur. We found that populations in the Canary Islands and Morocco closely matched those in the invaded North American range, and that this genetic cluster was most similar to the South African native range sites surrounding the Cape Town area and those from Aniston Village further east along the coastline. There was evidence of an invasion route from South Africa to the Mediterranean Basin, and that a secondary bridgehead invasion likely took place from there to North America. Genetic structuring within the native range revealed a total of four distinct populations, where sites north and south of Cape Town were unique and did not match the invasive populations. We found a unique outlier population in the Northern Cape which displayed intermediate morphological traits between C. crystallinum and its close relative, ice plant ( Mesembryanthemum guerichianum Pax; syn. Cryophytum guerichianum Pax). Surveys for biological control agents should focus on the areas between Kalk Bay and Yzerfontein in the Western Cape, and sites surrounding Arniston Village.
Abstract Burning nettle ( Urtica urens L.) and common groundsel ( Senecio vulgaris L.) are widespread, economically important weeds in horticultural systems. This laboratory and glasshouse study evaluated the effect of temperature, photoperiod, salinity, osmotic stress, and pH on seed germination, and the effect of burial depth on seedling emergence of these species. A significant interaction between temperature and photoperiod showed that germination depended on combined thermal and light cues rather than either factor alone. Urtica urens germinated higher in complete darkness (53%) than in light/dark (3%) across three temperature regimes studied. Germination peaked at 90% at 25/15C in complete darkness, while no germination occurred for this species at 15/5C and 35/25C day/night temperatures. In contrast, S. vulgaris preferred light/dark conditions (52% germination vs 29% in darkness), reaching 96% at 25/15C under day/night conditions. Salinity and osmotic stress inhibited germination of both species in a non-linear, sigmoidal pattern. Urtica urens germination was completely inhibited at ≥200 mM of sodium chloride (NaCl) and at ≤−0.6 MPa osmotic potential. Senecio vulgaris showed greater tolerance, with complete inhibition at ≥250 mM NaCl concentration and at ≤−1.0 MPa osmotic stress. Urtica urens germination peaked at pH 6 (92%) and declined under more acidic and alkaline conditions, while S. vulgaris germinated >97% across all pH levels (4 – 10). Urtica urens showed overall low emergence with 11% from soil surface and <1% when buried at different depths. In contrast, S. vulgaris showed up to 90% and 38% emergence from surface in sand and soil, respectively, but its seeds could not emerge beyond 0.5 cm burial depth. These findings can help refine integrated weed management in baby leaf crops by identifying periods when emergence is most likely, supporting timely stale seedbed or pre-emergence interventions, avoiding unnecessary soil disturbance when conditions favor germination, and prioritizing surface-focused control tactics for S. vulgaris .
Abstract Weed management is a primary barrier to sustainable organic vegetable production, and reducing the germinable soil weed seedbank is a critical long-term strategy for alleviating weed pressure. This study evaluated the effect of cover crops established in alleyways or traffic pathways on germinable warm-season weed seedbank density, species composition, functional group structure, and temporal emergence dynamics during transition to certified organic vegetable production. Treatments included three grass/legume cover crop bicultures of perennial ryegrass ( Lolium perenne L.)/white clover ( Trifolium repens L.), orchardgrass ( Dactylis glomerata L.)/red clover ( Trifolium pratense L.), sorghum-sudangrass [ Sorghum × drummondii (Steud.) Millsp. & Chas] /white sweet clover [ Melilotus officinalis (L.) Lam.], and a tilled fallow control. In the third year of the study, soil samples from cover-cropped and tilled fallow control pathways were subjected to a 60-day greenhouse emergence bioassay with observations recorded at 15, 30, 45, and 60 days after greenhouse setup. All three cover crop treatments reduced total germinable weed seedbank density by 73% to 82% relative to the tilled fallow, with no significant differences among cover crop treatments. Suppression was driven primarily by reductions in the annual broadleaf and annual grass functional groups, with carpetweed and foxtail identified as the principal species suppressed. Weed species richness did not differ among cover crop treatments or between cover crop treatments and the tilled fallow control. The tilled fallow produced a highly concentrated early emergence flush, with approximately 88% of total seedlings emerging within the first 15 days, whereas cover crop treatments substantially reduced and redistributed emergence across the monitoring period. Perennial ryegrass/white clover exhibited the most delayed peak emergence timing among all treatments. These findings demonstrate that traffic pathway cover cropping effectively suppresses the readily germinable warm-season weed seedbank during organic vegetable transition, with both annual and perennial cover crop bicultures providing equivalent suppressive benefits.
Abstract Spray drift and volatilization of the herbicide dicamba from agricultural uses has been an area of significant study in recent years. While only the low-volatility formulations of dicamba have been approved for use in the United States in postemergence dicamba-tolerant (DT) cotton ( Gossypium hirsutum L.) and soybean [ Glycine max (L.) Merr.], a variety of other dicamba products that are not specifically identified as low-volatility have been approved for decades and can be used as preemergence herbicides in certain crops, including soybean and cotton, and in early postemergence corn ( Zea mays L.) applications. This study compared the volatility and spray drift deposition resulting from an approved dicamba use on DT soybean, an approved dicamba use on corn, and an example of an unapproved use of dicamba on soybean all side by side in two locations. Results showed that the downwind spray drift deposition of dicamba was highest in the approved corn applications at both field locations due to medium droplet size and higher release height. The volatility of dicamba during the first sampling interval after application as measured by air concentrations was between 13 and 74 times higher for approved corn or unapproved soybean treatments at 1.5 m above the crop compared with approved soybean at both study locations. Results from this study suggest that the low-volatility formulations and label measures in DT soybean and cotton uses are beneficial in keeping dicamba off-target movement potential relatively low.
Wild radish (Raphanus raphanistrum L.) is a highly competitive annual broadleaf weed that significantly constrains wheat (Triticum aestivum L.) production, particularly under increasing herbicide resistance and limited chemical control options. Optimizing sowing geometry offers a practical, nonchemical approach to enhance crop competitiveness and suppress weed growth. A field study was conducted during 2022 and 2023 to evaluate the impact of different sowing geometries on R. raphanistrum suppression and wheat productivity. The experiment was arranged in a randomized complete block design with seven treatments, including broadcast sowing; line sowing at 11, 22, and 33 cm; ridge sowing (30 cm); bed sowing (60 cm); and cross sowing (22 cm). Sowing geometry significantly influenced R. raphanistrum density and biomass at all growth stages (15 to 45 d after sowing). Narrow spacing (11 cm) consistently resulted in the lowest weed density and biomass, while the wider 33-cm spacing resulted in the highest weed pressure. Crop growth and yield responses were consistent across years, with 11-cm line sowing producing the highest number of productive tillers (393.7 m-2), grains per spike (42.9), biological yield (15.4 Mg ha-1) and grain yield (6.0 Mg ha-1) averaged across 2 yr. This treatment was closely followed by cross sowing (22 cm). In contrast, wider spacing (33 cm) reduced grain yield by approximately 25% to 30% due to increased weed competition and reduced crop competitiveness. Correlation and principal component analyses revealed a strong negative association between late-season weed biomass and wheat productivity, emphasizing the importance of sustained weed suppression during critical growth stages. Overall, narrow row spacing, particularly 11-cm line sowing, enhanced crop competitiveness, effectively suppressed R. raphanistrum, and maximized wheat yield, demonstrating its potential as an eco-friendly strategy for integrated weed management.
Abstract Weed competition remains a major constraint to productivity in rice ( Oryza sativa L.)-based cropping systems, yet the ecological factors structuring weed communities across environments and management regimes remain insufficiently resolved in South Asia. This study examined weed community composition, diversity, and dominance in rice systems of Bangladesh and Nepal to assess how environmental conditions, crop rotation, and herbicide use shape weed assemblages. Weed community surveys were conducted in major rice-growing areas during 2016 and 2019 in Bangladesh and during 2019 in Nepal, covering 120 farmers’ fields per season across contrasting crop rotation systems (rice–fallow–rice and wheat ( Triticum aestivum L.)–jute ( Corchorus olitorius L.)–rice in Bangladesh; rice–wheat–fallow and rice–lentil ( Lens culinaris Medik.)–fallow in Nepal) and management regimes with and without preemergence herbicide use. We studied species richness, diversity, relative abundance, and frequency and their association with cropping system, weed management, land type, soil texture, and water management. Weed diversity and community composition varied significantly by site, year, cropping system, and herbicide use. Fields managed without herbicides consistently exhibited higher species richness and evenness, while herbicide use was associated with reduced diversity and dominance by fewer species. In Bangladesh, the wheat–jute–rice system supported higher weed diversity (0.96 to 1.01) than the rice–fallow–rice system (0.84 to 0.91), whereas in Nepal, weed community structure differed more strongly among locations than among crop rotations. Dominant species in Bangladesh included yellow nutsedge ( Cyperus rotundus L.), bermudagrass [ Cynodon dactylon (L.) Pers.], barnyardgrass [ Echinochloa crus-galli (L.) P. Beauv.], pickerelweed [ Monochoria vaginalis (Burm. f.) C. Presl. ex Kunth], cosmopolitan bulrush [ Bolboschoenus maritimus (L.) Palla]; syn.: Scirpus maritimus L.], and Paspalum spp., with relative abundance varying by land type and water regime. In Nepal, weed communities were characterized by recurring dominance of fimbry ( Fimbristylis littoralis Gaudich.), ricefield flatsedge ( Cyperus iria L.), C. dactylon , junglerice [ Echinochloa colona (L.) Link], pimpernels ( Lindernia spp.), and joyweeds ( Alternanthera spp.), with shifts in abundance linked primarily to site-specific hydrological and soil conditions. Farmer identification of troublesome weeds closely matched measured dominance patterns. These findings provide an ecological foundation for refining site-specific weed management strategies.
Abstract The global climate is changing, characterized by rising temperatures (projected to increase by 1.5–2 C by the end of the century) and elevated atmospheric CO 2 levels (>410 ppm), which are recognized as the primary drivers of climate change. These changes significantly affect multiple aspects of weed biology, including seed germination, seedbank dynamics, photosynthesis, root growth, phenology, and biomass production, often enhancing weed growth and competitive ability by 60% to 90% under elevated temperature and CO 2 conditions. Climate change not only modifies the biological traits of weeds but also influences the effectiveness of current management practices, including herbicide application, potentially increasing herbicide resistance. In this context, smart agriculture and artificial intelligence–based technologies offer promising tools for precise weed identification, monitoring of distribution patterns, and prediction of weed dynamics, thereby optimizing management strategies, reducing herbicide use, and improving control efficiency. Understanding climate-induced biological changes in weeds and integrating advanced technologies into management approaches are crucial for mitigating ecological threats and ensuring the sustainability of agricultural production.
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 ED 50 values, shikimic acid accumulation, and 14 C-glyphosate absorption and translocation in four biotypes collected from two Georgia fields, Jones (J) and Little Jones (LJ), in 2008 and 2023. Glyphosate ED 50 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 (A 95 ), 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.
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.
Abstract 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 ( I 2 = 97%), indicating context-dependent responses across systems. Successor crop yields showed an overall neutral response (mean lnRR = 0.052), with high between-study variability ( I ² = 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.
Abstract 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 (LD 50 ) 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 LD 50 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 LD 50 was 0.4407 g ha⁻ 1 (R 2 = 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.
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 screening 446 publications, 13 peer-reviewed articles met the inclusion criteria. Most studies were conducted in the subtropical United States, particularly in Florida, on bahiagrass ( Paspalum notatum Fluggé) pastures, with only one study carried out in Brazil. The most frequently reported herbicide was hexazinone, present in over 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 P. notatum 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 pre-emergence, 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 prior to 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 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.
Every year agriculture uses 2 million metric tons 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.
Abstract Winning the battle against weeds is crucial for sustainable rice ( Oryza sativa L.) production in sub-Saharan Africa (SSA), where weeds remain a leading cause of yield losses and continue to threaten the livelihoods of millions of smallholder farmers, with farms below 1 ha. This review evaluates the dynamic landscape of weed control strategies by examining weed ecology; the limitations of traditional hand weeding; and the growing risks associated with overreliance on herbicides, including escalating health concerns, environmental impacts, and the rapid rise of herbicide resistance. The central finding advanced in this review is that, despite the proven potential of integrated weed management (IWM) to provide sustainable and resilient weed control, its widespread adoption remains considerably low. Key barriers include weak extension services, low farmer awareness, and insufficient policy support, which collectively prevent timely and effective uptake of diversified weed control strategies. While approaches such as biological control, cover cropping, crop rotation, and precision tools hold promise, they remain underutilized without strong institutional backing. Drawing from case studies across the region, the review argues that IWM could deliver the most resilient and context-appropriate results if embedded within robust advisory systems and supportive incentives. The paper concludes with recommendations to strengthen extension capacity, promote farmer-centered innovation, and align policies to accelerate sustainable, scalable adoption of IWM across SSA.
Many rangeland weeds exhibit physiological seed dormancy that is released by cold winter temperatures. Species vary in their cold stratification requirements, leading to variation in the amount and timing of weed germination in the spring. We performed a replicated growth chamber study testing the impacts of stratification duration (0, 2, 4, 6, or 12 wk) on germination of common evening primrose (Oenothera biennis L.), Baldwin's ironweed (Vernonia baldwinii Torr.), tall goldenrod (Solidago altissima L.), and hollow Joe-pye weed [Eutrochium fistulosum (Barratt) E.E. Lamont]. Species (P < 0.001), stratification treatment (P < 0.001), and the interaction between species and stratification treatment (P < 0.001) jointly impacted the probability of germination. Stratification did not influence germination of O. biennis, although non-stratified seeds took longer to germinate. For V. baldwinii, positive effects of stratification were similar regardless of stratification duration (2 to 12 wk), although seeds stratified for 12 wk germinated fastest. Dissection revealed that most stratified V. baldwinii seeds failing to germinate did not appear to be viable. Germination of S. altissima was maximized at 4 wk of stratification, although seeds stratified for 12 wk again germinated fastest. In E. fistulosum, germination was maximized at 12 wk of stratification and time to germination decreased with increasing stratification duration. Overall, these results show flexible stratification requirements in these rangeland weeds, although longer stratification periods are generally associated with greater and faster germination. These data may be useful in predicting the timing of weed emergence to help guide management operations.
Amenity weed control remains a contentious issue, requiring a balance between maintaining plant growth below acceptable thresholds while simultaneously reducing the use of synthetic herbicides such as glyphosate. The environmental impact of three weed control methods: (1) herbicide only (glyphosate), (2) integrated weed management (IWM; maximum 50% total glyphosate active ingredient applied + mechanical and/or thermal), and (3) zero herbicide (mechanical and/or thermal alone) were evaluated. The herbicide-only method consumed the least amount of fuel, had the lowest fossil resource depletion, and emitted the fewest greenhouse gases of the three methods. Aquatic ecotoxicity was potentially higher, mainly due to the secondary metabolite of glyphosate, aminomethylphosphonic acid. The weighted aquatic ecotoxicity of IWM was 28% of that of the herbicide-only method. Fossil resource depletion was 24% of the zero-herbicide method but increased by a factor of 1.5 relative to the herbicide-only method, although the zero-herbicide method increased by a factor of 6.2 compared with the herbicide-only regime. Of the zero-herbicide methods evaluated, brushing and hot foam consumed the smallest quantities of fuel. Future weed control strategies should ideally focus on combined control methods that spatially target weeds for optimum control and low environmental impact depending on location. Weed control methods for amenity and environmental impacts in urban areas as part of an IWM strategy are discussed.
Understanding how crop species or communities influence weed seed mortality could effectively build ecological weed management systems. Therefore, we examined whether perennial forage monocultures or mixtures can accelerate weed seed mortality and affect the microbial composition of seeds. We buried mesh bags containing weed seeds of either Powell amaranth (Amaranthus powellii S. Watson) or velvetleaf (Abutilon theophrasti Medik.) in perennial forage treatments consisting of monocultures and mixtures of alfalfa (Medicago sativa L.), forage chicory (Cichorium intybus L.), and orchardgrass (Dactylis glomerata L.). Throughout a 2.5-yr duration, we evaluated seed mortality of both weed species and used 16S rRNA and internal transcribed spacer (ITS) amplicon sequencing to characterize A. powellii seed bacterial and fungal composition, respectively. We found limited effects of perennial forage treatment on A. theophrasti seed mortality, as the alfalfa-chicory biculture resulted in greater seed mortality compared with the orchardgrass monoculture. However, we found no other effects of perennial forage treatment on A. theophrasti or A. powellii seed mortality, nor did forage treatment affect the composition of bacteria or fungi associated with A. powellii seeds. We also found no effect of perennial forage richness on seed mortality of either weed species. Interestingly, soil cations (Ca, Mg, and K) tended to be negatively associated with weed seed mortality. Our research provided limited evidence that perennial forage communities can vary in their ability to accelerate weed seed mortality in the soil. However, we did uncover insights into microbial communities associated with weed seeds that could be promising for further research.
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 (ddRADseq) 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 rivet wheat (https://plants.sc.egov.usda.gov/plant-profile/AETA2) (Triticum turgidum L.; syn.: Triticum dicoccoides Koern. ex Schweinf.); 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.
