A trial involving two types of biochar was conducted in two greenhouse experimental runs in 2025 to determine weed control efficiencies of two pre-emergence herbicides (metribuzin and S-metolachlor) at respective label-recommended rates to control Palmer amaranth (Amaranthus palmeri S. Watson) and crowfootgrass [Dactyloctenium aegyptium (L.) Willd]. Plants were grown in a loamy soil amended with commercially available sugarcane and pinewood biochars (2 t ha-1). Complete control of both weeds was observed with the label-recommended doses of metribuzin and S-metolachlor in pinewood biochar-amended soils. Whereas in sugarcane (Saccharum officinale L.) biochar-amended soils, complete control of both weeds was achieved only with metribuzin at the label-recommended dose. The label-recommended dose of S-metolachlor provided nearly 47 and 74% control of A. palmeri and D. aegyptium, respectively, in sugarcane biochar-amended soils. Application of sugarcane biochar decreased the total residue of S-metolachlor as compared to soil with no or pinewood biochar and showed poor weed control efficiency (WCE). On day 7, nearly 3 and 24% germination for D. aegyptium and A. palmeri, respectively, were observed with S-metolachlor in sugarcane biochar-amended soils, whereas no germination was recorded in other treatments, which indicated biochar-herbicide-species specificity. Pearson correlation analysis showed negative associations between weed germination and soil herbicide residues across sampling times, though these relationships were not statistically significant (p > 0.05). Results from this greenhouse study indicated that commercial biochars from different raw materials could influence the WCE of pre-emergence herbicides even at a low biochar dose (2 t ha-1). Field evaluations are necessary to understand the weed control dynamics.

Weedy plants display enormous variation in the phenological traits that make up their life cycle both within and between populations. Facultative winter annual species are particularly interesting because they can adopt either a fall-emerging/spring-flowering or spring-emerging/summer-flowering life cycle at the population level via evolution or at the individual level via within-generation and transgenerational plasticity. Responses of phenological traits to the environment have often been found to be mediated by changes in hormone levels, especially the growth hormone gibberellic acid (GA). We conducted growth chamber and greenhouse experiments using the facultative winter annual Canadian horseweed (Erigeron canadensis L.; syn. Conyza canadensis (L.) Cronquist) to investigate the interactive effects of genetic variation; parent plant life cycle; and plastic responses to temperature, light, and GA treatments. We found that contrary to a prior report, exposing imbibed seeds to 3-4 weeks of cold (i.e., seed vernalization) does not always result in summer annual type growth, with considerable variation found among field-collected seeds from 10 populations. Further, seed vernalization and exogenous application of GA both tended to increase summer annual characteristics, interacting in ways that were largely consistent with the hypothesis that GA is a mechanism for cold-induced life cycle differentiation. Light treatment did not significantly affect life cycle traits, while parent life cycle type had marginal effects on offspring life cycle type. Finally, genetic variation among and within sites explained far less of the variation in life cycle traits than the plastic responses to seed vernalization and GA treatments. Our study proposes that the seasonality of this harmful agricultural weed is influenced by a GA-mediated response to vernalization of seeds during winter, yet highlights the need for further study, given the variability in this response. Insight into horseweed phenology is important for management given that intervention success depends on the timing of deployment relative to the weed’s life cycle.

Cereal rye (Secale cereale L.) cover crop provides a multitude of benefits, including soil conservation and weed suppression. Cereal rye biomass is positively correlated with weed suppression; however, high biomass is not always feasible. The weed-suppression potential of cereal rye grown under conditions that do not support high biomass is unknown. In such cases, other mechanisms, such as reduced soil temperature and nutrient depletion, may contribute to weed suppression. The objective of this study is to determine the impact of cereal rye biomass levels on soil water, temperature, nutrients, and, in turn, weed emergence patterns. Cereal rye was planted at four seeding rates (0, 20, 40, and 80 kg ha-1) and terminated at three timings (6, 4, and 2 weeks before planting cotton). Soil water and temperature were continuously monitored using automatic sensors. Soil nutrient content was analyzed from samples taken before cereal rye planting and at each termination timing. Weed seedling emergence was assessed throughout the summer. Cover crop termination timing had a greater influence on biomass production than seeding rate; delaying termination by four weeks resulted in 70 to 150% more biomass. High cereal rye biomass levels reduced maximum soil surface (0-10 cm) temperature by up to 7 C and thermal amplitude by 10 C before crop planting. Cereal rye significantly reduced soil nitrogen content but had minimal effect on phosphorus and potassium. A minimum biomass production of 2 t ha-1 is necessary for 30-50% weed suppression, whereas moderate (2 to 4 t ha-1) and high biomass levels (6000 kg ha-1) provided 60-70% and >90% weed suppression, respectively. The time for 50% weed seedling emergence was delayed by 18 days under high cereal rye biomass compared to fallow. Overall, our findings indicate that cereal rye suppresses weeds through multiple mechanisms, explaining suppression even at low biomass levels.

It is well established that cytochrome P450 monooxygenases (P450s) play a crucial role in herbicide metabolism and resistance evolution in weeds. In most documented cases, P450-mediated resistance is primarily conferred through the overexpression of P450 enzymes. However, the regulatory mechanisms underlying this overexpression remain poorly understood. In insects, amino acid substitutions that enhance P450-mediated metabolic detoxification have been clearly demonstrated as a key mechanism of insecticide resistance. In contrast, their potential role in herbicide resistance in weeds remains unclear. In this study, two CYP96A146 variants from flixweed [Descurainia sophia (L.) Webb ex Prantl], designated CYP96A146-S and CYP96A146-R, were heterologously expressed in Saccharomyces cerevisiae. These variants, which differ by four amino acid residues, were examined for their ability to metabolize model substrates and herbicides. The results indicated that both variants exhibited catalytic activity toward model substrates of p-nitroanisole, methoxyresorufin, ethoxyresorufin, 7-ethoxycoumarin, and benzo[a]pyrene, as well as toward the herbicides tribenuron-methyl, bensulfuron-methyl, and carfentrazone-ethyl. Notably, CYP96A146-R showed significantly higher catalytic activity than CYP96A146-S to both the model substrates (p-nitroanisole, methoxyresorufin, ethoxyresorufin, and 7-ethoxycoumarin) and the herbicides (tribenuron-methyl and carfentrazone-ethyl). These findings suggest that the amino acid substitutions are likely responsible for the enhanced metabolic capability of CYP96A146-R. Such mutations may induce conformational changes of CYP96A146 enzyme, facilitating more frequent molecular collisions between CYP96A146 and the substrates or herbicides, thereby improving catalytic efficiency.

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.

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