Palmer amaranth (Amaranthus palmeri S. Watson) is a highly competitive and drought-tolerant weed that poses significant challenges to U.S. agriculture due to its adaptability, prolific seed production, and herbicide resistance. Understanding how water stress at specific growth stages affects its development and seed production is critical for optimizing management strategies, particularly in water-limited environments. This study evaluated the effects of growth stage–specific water stress on growth and fecundity of A. palmeri under controlled greenhouse conditions. Four irrigation levels (100%, 80%, 60%, and 40% field capacity [FC]) were applied during vegetative and reproductive stages. Increasing water stress significantly reduced plant height, stem diameter, and biomass, with reductions of 17% to 35% under severe stress (40% FC). Total biomass declined by approximately 17% under severe water limitation. Root biomass at 60% FC decreased by 13% to 14% relative to 100% FC, whereas root length density increased by 11% to 16%, indicating adaptive root elongation under severe water deficit conditions. Despite reductions in vegetative growth, A. palmeri maintained high reproductive capacity. Seed production at 100% FC was 48% to 72% higher than at 80% FC and more than 2- to 3-fold greater than at 60% FC. Furthermore, plants subjected to reproductive-stage stress produced approximately 29% more seeds than those stressed during the vegetative stage, highlighting strong stage-dependent reproductive plasticity. Seed germination was highest at 100% FC but declined by approximately 55% at 60% FC. In contrast, germination at 80% FC remained within 10% of optimal levels and was comparable under 40% FC, suggesting a nonlinear response and potential maternal effects enhancing seed resilience under stress. The study revealed the importance of early-season weed control to exploit periods of vulnerability and limit seedbank replenishment. Overall, this study provides valuable insights for integrating weed management strategies in dryland cropping systems, where water scarcity and herbicide resistance present ongoing challenges.

This study investigated the effects of essential oils (EOs) from rosemary (Rosmarinus officinalis L.) and Shirazi thyme (Zataria multiflora Boiss.) on the early growth and physiological characteristics of three weed species: Amaranthus retroflexus L., Chenopodium album L., and Cirsium arvense (L.) Scop. conducted at Razi University. the experiment utilized a factorial design with varying concentrations of EOs in laboratory (0.5, 1, 2, 5, 10, and 20 µL mL⁻¹) and greenhouse (5, 10, and 20 µL mL⁻¹) settings. Control treatments included distilled water, distilled water + Tween 20 (1%), and trifluralin and glyphosate. GC-MS analysis revealed 15 major compounds in rosemary EO and 23 in Shirazi thyme EO. A significant inhibition of plumule and radicle lengths was reported across all species. In greenhouse trials, Shirazi thyme EO at 10 and 20 µL mL⁻¹ reduced stem length by up to 75.2% and 74.5% in A. retroflexus, surpassing reductions caused by rosemary EO (57.2% at 20 µL mL⁻¹) and glyphosate (65.2%). Root length reductions were most pronounced with Shirazi thyme EO, reaching up to 83.9% inhibition in A. retroflexus at 10 µL mL⁻¹, exceeding effects of rosemary EO and glyphosate. Shirazi thyme EO causing up to 54.4% reduction in stem dry weight of C. arvense and 82.7% reduction in root dry weight of A. retroflexus. Leaf greenness, photosynthetic efficiency, and maximum quantum yield of photosystem II (PSII) also decreased markedly with increasing EO concentrations, particularly under Shirazi thyme EO, which in some cases completely abolished photosynthetic efficiency, outperforming glyphosate.

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.

Trifludimoxazin + saflufenacil is a premix PPO-inhibiting herbicide with preemergence and postemergence activity pending USEPA registration for burndown application ahead of planting corn (Zea mays L.), soybean [Glycine max (L.) Merr.], grain sorghum [Sorghum bicolor (L.) Moench], and wheat (Triticum aestivum L.). With early season soybean growth often occurring simultaneously with preplant burndown of fields in later planted soybean and grain sorghum, odds of negative impacts associated with off-target herbicide movement to the crop increase. Field studies were conducted in 2024 to evaluate effect of reduced rates of trifludimoxazin + saflufenacil (12.5% to 0.4% of the lowest proposed labeled application rate of 38.3 g ai ha-1) applied to 1- to 2-leaf soybean. Reduced rates of 1/8, 1/16, 1/32, and 1/64x resulted in 53%, 43%, 32%, and 21% visual phytotoxicity 1 week after treatment (WAT) while at 4 WAT response was 31%, 23%, 17%, and 12%. Trifludimoxazin + saflufenacil at these rates reduced soybean height 30% to 7% and 18% to 4% 1 and 4 WAT, respectively. Soybean yield was negatively impacted 8%, 5%, 2% and 0% at these respective rates. Off-target movement of trifludimoxazin + saflufenacil to soybean in early vegetative growth will result in severe visual injury and height reduction, especially with exposure at the three highest rates evaluated. Soybean should not be expected to fully recover and significant negative impact on yield (5% or greater) will be observed at the two highest rates evaluated in this research.

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.

High-quality bermudagrass [Cynodon dactylon (L.) Pers.] forage production is a vital component of southeastern U.S. agriculture. Previous research indicates that environmental stresses like elevated CO2 may significantly affect crop productivity, weed competitiveness, and ecological shifts. Although the effects of elevated CO2 on C4 plants like bermudagrass could be marginal, the growth, vigor, and herbicide tolerance of C3 weeds can be affected profoundly. In the final 2 yr of a 7-yr study investigating the effects of management practices and elevated CO2 levels on bermudagrass forage production, we aimed to evaluate how these treatments impacted weed competition and diversity. From 2018 to 2025, bermudagrass was grown in a coarse-textured soil bin at the USDA-ARS National Soil Dynamics Laboratory in Auburn, AL. Open-top chambers delivered either ambient or elevated CO2 (+ 200 mg kg−1), and plots were either managed annually with fertilizer and herbicide or left unmanaged. In the final 2 yr, elevated CO2 had no significant effect on total biomass production (bermudagrass + weeds), but in unmanaged plots, elevated CO2 resulted in a significantly greater proportion of weeds. While some C4 grasses and sedges were observed in this experiment, most weed species were C3. Consequently, C3 species dominance was generally high, especially in managed plots exposed to elevated CO2. Weeds were observed and identified in all plots, but those managed with fertilizer and herbicide had a greater proportion of bermudagrass plants to weeds, as well as lower weed densities. Species diversity indices yielded significantly greater species richness under elevated CO2 conditions. Moreover, we observed greater weed diversity with elevated CO2, which was exacerbated without proper nutrient and weed management. This provides compelling evidence that substantial shifts in weed diversity could occur due to environmental change factors like elevated CO2 and the lack of a proper crop management program.

Seed germination responses to light influence the timing of weed emergence and management outcomes. We evaluated (1) variation in light-dependent germination among germplasm sources, (2) the relationship between primary dormancy and far-red light–enforced germination inhibition, and (3) the role of seed size in light-dependent dormancy. Between 2022 and 2025, germination of 70 kochia [Bassia scoparia (L.) A. J. Scott] populations and 49 common lambsquarters (Chenopodium album L.) accessions was evaluated under three light environments—dark, red, and far red—for both freshly harvested and stored seed. Bassia scoparia germination did not differ among light environments (ANOVA, P = 0.67), indicating weak photoblastic regulation at the species level. In contrast, C. album exhibited pronounced differences in light-dependent germination among accessions (P < 0.0001). Accessions with greater primary dormancy, defined as the difference between germination of freshly harvested and stored seed, exhibited stronger far-red-enforced germination inhibition, indicating coordinated regulation of dormancy depth and light sensitivity. Seed weight was not strongly associated with primary dormancy (Spearman’s ρ = 0.057, P = 0.11) or far-red suppression (ρ = 0.50, P = 0.06). These results indicate that variation in light-dependent dormancy and germination in C. album is governed primarily by genetic and physiological regulation of light perception rather than by seed size.

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.

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.

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.

Herbicide resistance in Palmer amaranth (Amaranthus palmeri S. Watson) continues to threaten the sustainability of cotton (Gossypium hirsutum L.) production in the U.S., partly because management programs often emphasize in-season suppression without sufficiently limiting the number of individuals repeatedly exposed to postemergence herbicide selection. A five-year large-plot field experiment (2019–2023) was conducted to evaluate four integrated weed management (IWM) components, zero tolerance for seedbank replenishment (ZT–SBR), occasional deep inversion tillage (Occ_DIT), cereal rye cover crop (CRCC), and dicamba-inclusive herbicide programs (Dic_inCrop), applied singly, in combination, or absent altogether in a conventional four-pass base program lacking all four components. Preemergence escapes, defined here as emerged A. palmeri surviving the residual herbicide preceding each pass, were quantified at each timing and analyzed as annual trajectories and five-year cumulative exposure (a proxy for accumulated postemergence selection). In 2024, legacy emergence was measured under unmanaged conditions. Occ_DIT strongly structured temporal trajectories, inducing an immediate low-density state (12% of the base program in Year 1) versus gradual decline without Occ_DIT (∼75% in Year 1; steep early slope), yielding markedly lower cumulative preemergence-escape pressure. Across five years, cumulative exposure was most reduced by Occ_DIT, followed by Dic_inCrop, CRCC, and ZT–SBR, with significant interactions indicating non-additive benefits. In the legacy year, main-effect incidence rate ratios (IRRs) showed substantial suppression by Dic_inCrop (IRR = 0.02), ZT–SBR (IRR = 0.02), Occ_DIT (IRR = 0.06), and CRCC (IRR = 0.24), with four-way combinations reducing emergence by >98% relative to the base program. Positive interaction IRRs reflected diminishing marginal returns near the ecological floor, not antagonism. Collectively, these results demonstrate that IWM efficacy at low weed densities is governed less by additive suppression than by how mortality is repartitioned across independent demographic bottlenecks, reinforcing the value of diversified IWM as an evolutionary risk-management strategy.

Parthenium weed (Parthenium hysterophorus L.) is rapidly invading southern Oman, posing growing challenges to agricultural productivity and rural livelihoods in Dhofar’s crop–livestock systems. This study assesses its agronomic and socioeconomic impacts using field surveys and a stratified household survey of 40 farms conducted between June and August 2022. Data were analyzed using partial least-squares structural equation modeling (PLS-SEM) to examine the relationships between farmer characteristics, infestation levels, weed management practices, and farm revenue. Results indicate that while most farmers are aware of P. hysterophorus, limited recognition at early growth stages delays control and increases management costs. Education (β = 1.009, P = 0.06), cultivated area (β = 1.033, P = 0.003), and chemical control expenditures (β = 0.295, P = 0.05) were positively associated with gross revenue, whereas age had a negative effect (β = −0.762, P = 0.08). Infestation significantly increased labor-intensive weeding costs (β = 2.072, P = 0.07) but reduced chemical use (β = −1.303, P = 0.032), indicating substitution toward manual control. Although time spent uprooting parthenium reduced infestation levels (β = −0.128, P < 0.001), it also increased weeding and chemical control costs, highlighting the financial burden of relying on manual methods. Crop-specific analysis showed heterogeneous vulnerability, with peas (Pisum sativum L.) more affected than wheat (Triticum aestivum L.) and tomato (Solanum lycopersicum L.). Overall, the findings demonstrate that parthenium imposes measurable income and welfare risks on farming households. These impacts can be mitigated through farmer education, early detection, and judicious chemical use within an integrated weed management framework. Strengthening extension services and promoting crop-specific interventions are essential for protecting rural livelihoods and food security in arid, invasion-prone farming systems.

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 CO2 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 CO2 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.

Italian ryegrass [Lolium perenne L. ssp. multiflorum (Lam.) Husnot] is one of the most common and malignant weeds that seriously affect wheat (Triticum aestivum L.) yield. Investigating its germination ecology and competitive dynamics with wheat is essential for predicting its potential invasion areas and developing effective management strategies. This study evaluated the effects of key environmental factors (pH, temperature, light, salinity, osmotic stress, and burial depth) on the seed germination and emergence of L. perenne ssp. multiflorum, and further quantified the impact of varying weed densities on wheat yield. The results showed that L. perenne ssp. multiflorum exhibits broad adaptability to environmental conditions. Optimal germination (70% to 86%) occurred at constant temperatures of 10 to 25 C. High germination rates (84% to 98%) were sustained across a wide pH range (4 to 10). Germination remained above 50% at osmotic potentials as low as −0.7 MPa. The germination rate of L. perenne ssp. multiflorum decreases with the increase in salt concentration, and was completely inhibited at 300 mM NaCl. Emergence was highest (92%) at 2-cm burial depth, remained above 80% from 0.5 to 6 cm, declined sharply beyond 10 cm, and was negligible at 14 cm. Field experiments demonstrated a density-dependent reduction in wheat yield by competition from L. perenne ssp. multiflorum, primarily through decreased wheat spike density and grains per spike, thereby reducing yield. Increasing wheat sowing density from 67.5 to 202.5 kg ha−1 could significantly mitigate these losses. These findings provide critical insights into the ecological adaptability of L. perenne ssp. multiflorum and its potential impact on agricultural systems, which can inform integrated weed management strategies.

Strategic soil inversion is advocated as a periodic weed management strategy, typically recommended every 4 to 8 yr if the goal is to delay the evolution of herbicide resistance. It is assumed that the weed seeds buried during the inversion process will lose viability during this period. However, long-term seedbank persistence following soil inversion has not been investigated. If the buried seeds retain viability, subsequent inversions or other deep-tillage operations may return them to the soil surface, potentially replenishing the weed seedbank. The current study identified 30 sites within the wheatbelt of Western Australia (in 2020) that had previously been subject to a single soil inversion event, to investigate viability of the buried seed. At each site, soil was sampled at 10-cm increments from 0 to 40 cm, and weed seedling emergence from these samples was assessed during the following year. Weed emergence was dominated by six species: rigid ryegrass (Lolium rigidum Gaudin), subterranean clover (Trifolium subterraneum L.), prostrate knotweed (Polygonum aviculare L.), clammy goosefoot [Dysphania pumilio (R. Br.) Mosyakin & Clemants], capeweed [Arctotheca calendula (L.) Levyns], and ripgut brome (Bromus diandrus Roth). Weed emergence was greatest from the 10- to 20-cm soil depth, with limited weed emergence beyond this depth, despite inversion operations generally placing topsoil below 20-cm depth. Of the six predominant species, the seedbank persisted for at least 8 yr, except for B. diandrus. This species did not emerge from sites where the inversion was performed more than 2 yr before the survey. This likely reflects species-specific differences in seed size and seedling emergence depth, as B. diandrus produces relatively large seeds capable of emerging from 10 to 20 cm (i.e., the most common burial depth). The findings confirm that the buried seedbank for most species remains viable over extended periods.

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.

Glufosinate-ammonium (GA) has been widely used in U.S. 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 20% 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 3× 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 point 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% to 92% at 30/20 C and remaining high (72% to 88%) at 35/25 C, indicating strong adaptation to warm climates. Both populations germinated well in light/dark (12/12 h) conditions (87% to 93%), while BG3 showed a reduction (80%) in complete darkness (24 h) compared with light/dark conditions, suggesting weak positive photoblastic behavior. 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 [Sorghum bicolor (L.) Moench] 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 semiarid 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 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 uniform, 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 that is 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 were used to determine population structure and potential source populations. Pontederia cordata has low genetic diversity within and among invasive populations in SA compared with 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.