Sorgoleone, an allelochemical exuded from root hairs of grain sorghum [Sorghum bicolor (L.) Moench], has proven herbicidal activity on several weeds and crops. Due to its hydrophobic nature and affinity for organic matter, sorgoleone can persist in the soil for a long period. While beneficial for weed suppression, growers in the southeastern United States have raised concerns that sorghum residues may negatively affect wheat [Triticum aestivum L.] emergence in double-crop systems. Two independent laboratory studies were conducted to evaluate sorgoleone activity: (1) Weed Species/Wheat Variety Study, which included four weed species Italian ryegrass [Lolium perenne L. ssp. multiflorum (Lam.) Husnot], large crabgrass [Digitaria sanguinalis (L.) Scop.], sicklepod [Senna obtusifolia (L.) H.S. Irwin & Barneby], and velvetleaf [Abutilon theophrasti Medik.] and two wheat varieties, USG3251 and Shirley, and (2) Wheat Variety and Group Study, which included a total of 20 varieties distributed in four wheat group. In both studies, sorgoleone was applied at 0.025, 0.05, 0.10, 0.15, 0.20, and 0.30 g L-1 to seeds grown in petri dishes under laboratory conditions. In study (1), sorgoleone activity had a stronger effect on grass weeds than on broadleaf weeds. Lolium perenne ssp. multiflorum was the most susceptible weed, showing 77% growth reduction at 3 g L-1 of sorgoleone. At the same concentration, D. sanguinalis showed the second-highest response with a 32% growth reduction, followed by A. theophrasti and S. obtusifolia, with reductions of 23% and 20%, respectively. No effect of sorgoleone was observed on wheat varieties. In study (2), growth reduction was only observed for six wheat varieties at the highest sorgoleone concentrations. Furthermore, between groups, Hard Red wheat presented higher response to sorgoleone compared to the other groups. These findings demonstrate strong herbicidal activity of sorgoleone on grass weeds, particularly L. perenne ssp. multiflorum, while having minimal effects on most wheat varieties.

There is scant information about seed germination and seedling emergence of common evening primrose (Oenothera biennis L.), even though it is a common and widespread weed in North America. This study was conducted to determine the influence of several environmental factors on its seed germination and seedling emergence from three North American populations in autumn. In alternating light (12 h)/darkness (12 h), maximum germination (89.7-97.7%) of freshly matured seeds occurred at alternating temperature regimes ≥ 25/15 C, and germination was lowest (0-80.3%) at the coolest temperature regime of 15/5 C. In comparison to seeds incubated with an alternating light/dark photoperiod, germination was lower when seeds were exposed to continuous darkness, indicating that seeds were positively photoblastic. Cold stratification at 4 C enhanced germination, with seed dormancy alleviated after 4-8 wk depending on the study population. For freshly matured seeds, germination exceeded 67% in test solutions ranging from pH 3 to 10, and was highest (80-100%) at neutral or near-neutral pH. Germination exceeded 84% in solutions with osmotic potentials ranging from 0 to -0.4 MPa, and germination was observed at osmotic potentials as low as -0.8 to -1.0 MPa depending on the study population. Seedling emergence was only observed for seeds sown on the surface of soil or buried to depths ≤ 2 cm. Thus, seeds of O. biennis are positively photoblastic and exhibit germination characteristics associated with type 2 non-deep physiological dormancy at maturity, with seeds being capable of germinating under a variety of climatic and edaphic conditions.

Indaziflam is a long-term residual weed control option for Georgia pecan [Carya illinoinensis (Wangenh.) K. Koch] growers. As a nonselective cellulose biosynthesis inhibitor, indaziflam has a niche for broad-spectrum weed control with long residual activity in various perennial cropping systems. Indaziflam’s soil persistence and chemical behavior at various temperatures have not been fully evaluated; therefore, the objectives of these experiments were to: (1) quantify indaziflam soil dissipation under field conditions in two common Georgia soils and (2) evaluate indaziflam molecular stability as affected by temperature and time using laboratory techniques. Indaziflam soil dissipation followed first-order kinetics and was adequately described by the exponential decay equation. Indaziflam half-life in Greenville sandy clay loam and Faceville loamy sand was 96 and 78 d, respectively. Indaziflam half-life and soil clay content had a direct relationship, while indaziflam half-life and microbial biomass had an inverse relationship. Aqueous solutions of indaziflam were exposed to temperatures that ranged from 20 to 70 C for up to 672 h, with results indicating that temperature had no influence on indaziflam’s molecular stability.

In the summer of 2016, a case of potentially herbicide-resistant redroot pigweed (Amaranthus retroflexus L.). Amaranthus retroflexus was reported in Saint-Louis-de-Gonzague (Qc, Canada) in an identity preserved soybean [Glycine max (L.) Merr.] field where imazethapyr and chlorimuron-ethyl were applied pre-emergence, two active ingredients that inhibit acetolactate synthase (ALS). A few years earlier, several A. retroflexus populations resistant to ALS inhibiting herbicides were reported in Manitoba (MB). Amaranthus retroflexus samples from these fields were collected and analysed to characterize the presence of a resistance mechanism and the associated level of resistance. Sequencing of the ALS gene revealed a mutation resulting in a serine to asparagine substitution at amino acid position 653. Dose response experiments indicated resistance factors of 27.7 to 194.0 to imazethapyr (imidazolinones) among these populations, but susceptibility to members of all other ALS inhibitor families that were tested. In one MB population a serine to isoleucine substitution at position 653 was observed for the first time in A. retroflexus in some of the plants and this contributed to the detection of resistance to thifensulfuron-methyl when compared with most susceptible control population. The response of the two MB control populations to thifensulfuron-methyl differed and R factors were influenced by the level of susceptibility of the control populations to thifensulfuron-methyl. The same was not observed with imathezapyr. Non-target site resistance (NTSR) was not detected in the MB populations when exposed to malathion prior to exposure to the herbicide. We identified two new mutations on the ALS gene in A. retroflexus that result in ALS inhibitor specific cross-resistance patterns. Further investigation into NTSR and the mechanism behind the differential response of the control populations to thifensulfuron-methyl are warranted.

Butachlor is an herbicide extensively employed in rice cultivation, which has historically been under-investigated for its toxicological impacts on terrestrial vegetation. This study examines the dose-dependent effects of butachlor on the germination and antioxidant defense mechanisms in the seeds of Asian tape grass [Vallisneria natans (Lour.) H. Hara], an important submerged plant species widely distributed in the agricultural ponds. Employing a hydroponic setup, seeds were exposed to four concentrations of butachlor (0, 20, 200, and 2000 μg active ingredients L-1), and cultivated under controlled light conditions to quantify germination rates and assess oxidative stress responses. Our findings showed that butachlor concentrations up to 20 μg L-1 had no effect on the germination rate of V. natans seeds, while germination rates decreased by 6.0% and 8.7% at 200 and 2000 μg L-1, respectively. At 2000 μg L-1, malondialdehyde (MDA) content increased by 5.7 nmol g-1 FW, and catalase (CAT) activity declined by 21%, indicating oxidative damage. Additionally, the antioxidants proline (Pro) and glutathione (GSH) were upregulated under 20 μg L-1 butachlor treatment after 12 h, contributing to reactive oxygen species (ROS) scavenging and cellular stability. This study highlights the nuanced interactions between butachlor exposure and the antioxidant defenses in V. natans, providing valuable insights into the ecological impacts of herbicide pollution. Understanding these interactions is crucial for developing sustainable agricultural practices and for the management of herbicide resistance in aquatic systems.

Annual bluegrass (Poa annua L.) is a globally distributed weed species with the ability to evolve resistance to herbicides. Oregon hazelnut (Corylus avellana L.) growers have recently reported poor control of P. annua with clethodim, pendimethalin, paraquat, and glyphosate, raising concerns about new herbicide-resistance cases. To investigate these reports, we conducted a herbicide resistance survey of field-collected accessions using seed-based and whole-plant dose–response bioassays. Based on dose–response estimates, resistance to all four herbicides was confirmed. Clethodim-resistant accessions had resistance indices (RIs) of 2 to 10 compared with susceptible accessions with seed-based LD50 values of 0.4 to 0.5 µM and whole-plant LD50 values of 14 to 19 g ha⁻¹. Pendimethalin-resistant accessions had RIs of 3 to 47 compared with susceptible accessions with seed-based LD50 values of 0.5 to 1 µM and whole-plant LD50 values of 360 to 590 g ha⁻¹, and cross-resistance to pronamide was also confirmed (RI = 7 to 16; susceptible accessions LD50 = 550 to 600 g ha⁻¹). The glyphosate-resistant accession had RIs of 2 to 6 compared with susceptible accessions with seed-based LD50 values of 340 to 490 µM and whole-plant LD50 values of 60 to 95 g ha⁻¹. Paraquat-resistant accessions had RIs of 2 to 85 compared with susceptible accessions with seed-based LD50 values of 0.6 to 1 µM and whole-plant LD50 values of 30 to 50 g diquat ha⁻¹. This study documents the first global case of clethodim resistance in P. annua, pendimethalin and glyphosate resistance in Oregon, and paraquat resistance in P. annua in the United States. We also demonstrate, for the first time, that seed-based bioassays can detect clethodim and paraquat resistance in P. annua. Seed assays provided a rapid (2 wk), cost-effective diagnostic tool suitable for on-farm implementation and complementary to molecular diagnostics. These findings underscore the urgent need for integrated weed management in perennial systems and adoption of resistance diagnostics and stewardship programs to mitigate further resistance evolution.

Cereal rye (Secale cereale L.) is grown as a cover crop due to its ability to enhance soil health and suppress weeds through allelopathy, but germination responses of different weed species to allelochemicals have not been studied for seeds varying in age and consequently vigor. This study investigated the allelopathic effects of cereal rye on the germination of Palmer amaranth (Amaranthus palmeri S. Watson), large crabgrass [Digitaria sanguinalis (L.) Scop.], giant foxtail (Setaria faberi Herrm.), and lettuce (Lactuca sativa L.). Seeds were germinated in vitro in media with allelochemicals secreted by roots of cereal rye lines varying in allelopathic activity. Seeds were subjected to an accelerated aging treatment to modify their vigor. Results showed that aged seeds exhibited 31% lower germination than non-aged seeds. The magnitude of the germination reduction due to the presence of allelochemicals was species dependent. In the absence of allelochemicals, L. sativa exhibited a 20% reduction in germination due to aging, while the reduction was greater than 60% when allelopathy and aging were combined. Non-aged S. faberi seeds increased germination under low allelopathy conditions, with 20% greater germination compared with the non-treated control. Digitaria sanguinalis did not respond to seed aging, and the high allelopathy treatment reduced germination less than 10%. Amaranthus palmeri exhibited the highest germination and was the only species that was not affected by the seed aging and allelopathy treatments. Germination rate was reduced by seed aging and to a lesser extent by allelochemicals. Results suggest that incorporating allelopathic S. cereale varieties in cover crop rotations can reduce weed populations. However, the age structure of the seedbank might determine the importance of allelochemicals for emergence at the species level, likely causing weed community shifts.

Integrated weed management (IWM) is essential for organic farming cultivation. However, an increased weed presence has been found on a farm that applies crop rotations, certified seed, high seeding rate, and false seedbed. This study aimed to evaluate the effect of false seedbed versus conventional tillage on weed dynamics on the field bean crop (Vicia faba L. ‘Minor’) after 3 yr of application of crop rotation (field bean, sunflower [Helianthus annuus L.], and durum wheat [Triticum durum L.]) and IWM strategies. The field bean 2024 false seedbed (FB24Fs) yield was 0.9 Mg ha−1, less than half of the field bean 2024 conventional (FB24C) yield (2 Mg ha−1). About 66% of total aboveground biomass (AGBt) was related to wild oat (Avena fatua L.) in FB24Fs at harvest. The yield and AGB results at harvest can be explained by the evolution of crop and weed density dynamics. For FB24Fs, the crop plant number (PNc) at germination (G) was 30 m−2, the weed plant number density (PNw) at G was 74% of the total (PNt), with predominance of monocotyledons, PNm (62%). The delay in crop seeding, germination, and environmental and soil differences affected early weed germination and high weed competitiveness. Employing repetitive cultivation strategies, such as false seedbed and late sowing, can lead over time to the selection of a few competitive weeds.

There is a high demand for cultural weed management strategies targeting Palmer amaranth (Amaranthus palmeri S. Watson) in furrow-irrigated rice (Oryza sativa L.) production due to overreliance on herbicides and the lack of a continual flood to prevent weed emergence. Amaranthus palmeri has been shown to reduce corn (Zea mays L.), cotton (Gossypium hirsutum L.), and soybean [Glycine max (L.) Merr.] yields when it interferes with the crop. However, minimal research has been conducted to assess the ability of this weed species to impact rice grain yield. The manipulation of rice seeding rate to enhance rice canopy formation and favor the crop over the weed have not been fully explored. Hence, research was conducted to 1) evaluate the effect of rice density on A. palmeri emergence, rice canopy cover, and relative yield, and 2) determine the impact of A. palmeri density and aboveground biomass on rice grain yield. A natural population of A. palmeri was allowed to emerge at varying densities throughout the growing season within furrow-irrigated rice. Amaranthus palmeri plants caused 12 to 87% yield loss at densities ranging from 1 to 20 plants m-2, and yield loss was 45 to 80% for plants weighing 200 to 800 g m-2. When furrow-irrigated rice was sown at various densities, crop canopy cover increased as rice plant density increased. Most A. palmeri emergence occurred within the first four weeks after rice emergence, before canopy formation could have an effect. Amaranthus palmeri emergence beyond 5 weeks after rice emergence decreased as rice plant density and canopy cover increased. These results indicate that A. palmeri has the potential to cause severe yield loss, and that residual herbicides will be vital for A. palmeri management in a furrow-irrigated rice system, due to the continual emergence of weeds up to crop canopy formation.

Cover crops and soil-residual herbicides are considered essential tools within integrated weed management practices. However, interception of soil-applied herbicides by cover crop residue can reduce weed control and crop yield. Field trials were conducted in 2022 and 2023 in Indiana to investigate the effect of cereal rye (Secale cereale L.) termination strategies on the concentration of sulfentrazone, S-metolachlor, and cloransulam-methyl in soil, weed control, and soybean [Glycine max (L.) Merr.] yield. Soybeans were planted at cereal rye anthesis. Termination strategies included roller-crimped cereal rye, standing cereal rye, and a fallow control. The average cereal rye biomass in 2022 and 2023 was 4.06 and 14.2 Mg ha−1, respectively. Soybean stands were unaffected in 2022 but were reduced by 24% and 69% in the presence of roller-crimped and standing cereal rye, respectively, in 2023. On average, 75% and 84% of the soil-residual herbicides applied were intercepted by the roller-crimped cereal rye residue in 2022 and 2023, respectively. The use of cereal rye did not improve overall weed control relative to fallow at 18 after soybean planting in 2022 and 2023. In 2022, roller-crimped cereal rye reduced soybean yields by up to 13% in comparison with the fallow. In 2023, regardless of management strategy, the use of cereal rye as a cover crop reduced soybean yields by an average 44% in comparison to the fallow. Results from this research suggest that the adoption of the planting green system can significantly reduce soybean yield primarily due to stand losses if proper planting equipment is not used. Furthermore, the high levels of cereal rye biomass achieved in both years of the study did not provide additional season-long weed suppression relative to the non-cover crop control.

Targeted sprayers use artificial intelligence to enable on-the-go weed detection and herbicide application, reducing the need to spray entire fields with foliar herbicides. A targeted sprayer was evaluated for treating weeds in corn (Zea mays L.) and soybean [Glycine max (L.) Merr.] cropping systems in the midwestern United States. Using a ONE SMART SPRAY sprayer, our objectives were to (1) evaluate the efficacy of different herbicide application programs: two-passes, spot-spray (SS) only, or simultaneous broadcast residual and SS foliar herbicides; (2) determine whether weed detection thresholds influence weed control; and (3) determine the cost for each herbicide program compared with a traditional broadcast application. Field experiments were conducted in 2022 and 2023 near Manhattan, KS, and in 2023 in Seymour, IL. Both green-on-brown (GOB; burndown applications) and green-on-green (GOG; in-crop applications) were applied. Main plot treatments consisted of four herbicide programs, and the split-plot consisted of four weed detection thresholds: herbicide Efficacy, Balanced, Savings, and a Broadcast application. The percentage of area infested with weeds within each plot was estimated visually 42 d after the GOG application. An “as-applied map” was constructed using raw sprayer data to show when nozzles were turned on or off within a subplot and used to determine herbicide program costs based on the percentage of each plot area sprayed. Results indicated that herbicide programs with simultaneous broadcast and SS components in many cases resulted in a similar area infested with weeds compared with broadcast applications with the same herbicide products. As expected, herbicide costs were lower in SS applications than in broadcast applications. The ONE SMART SPRAY sprayer demonstrated potential to reduce herbicide input costs without compromising weed control.

Earthworms are postdispersal seed predators that can influence weed communities in temperate agroecosystems. Recent studies have found that seed feeding by earthworms tends to be driven by the active selection of certain seed species rather than random encounter. Numerous seed traits are expected to affect seed selection by earthworms, including seed size, shape, coat hardness, and nutritional content. The impact of these traits on seed selection by earthworms tends to vary depending on seed species identity and earthworm species identity, rendering the outcome of earthworm–seed interactions hard to predict. We carried out laboratory experiments to investigate the impact of seed physical and chemical traits on seed choice by the common earthworms (Lumbricus terrestris). Seeds of six weed species typical of the Northern Great Plains agroecosystem, wild mustard (Sinapis arvensis L.), field pennycress (Thlaspi arvense L.), shepherd’s purse [Capsella bursa-pastoris (L.) Medik.], catchweed bedstraw (Galium aparine L.), green foxtail [Setaria viridis (L.) P. Beauv.], and redroot pigweed (Amaranthus retroflexus L.), were offered to L. terrestris in multiple-choice feeding arenas. The results showed that seeds of S. arvensis and C. bursa-pastoris, both of which have high lipid content, were the most consumed. Seed ingestion was negatively influenced by irregular seed shapes and long seed length, but these physical traits did not override the strong preference for lipid-rich seeds. These findings suggest that seed selection by L. terrestris earthworms was strongly influenced by the lipid content of the seed when seed morphology (i.e., size and shape) varied within certain limits. Therefore, seed nutrients are likely to play an important role in weed seed choice by L. terrestris earthworms when seed physical traits do not impose major constraints on ingestion.

Chinese stellara (Stellera chamaejasme L.) is an indicator plant of degraded grasslands. With its robust vitality, once it emerges in grassland ecosystems, it undergoes extensive growth and rapid expansion, inevitably leading to grassland degradation. The establishment and invasion of S. chamaejasme disrupts the ecological balance of grasslands in the Qilian Mountains. This study was conducted in a grassland on the eastern slope of the Qilian Mountains, employing point pattern analysis to investigate the spatial distribution patterns of S. chamaejasme and the relationships among different age classes. The population was categorized into three growth stages: young, subadult, and mature plants. The results revealed that the spatial distribution of this population is primarily dominated by subadult plants, accounting for up to 75.48% of the total, with an overall transition trend from aggregated to random distribution. No significant spatial correlations were observed among different age groups (young, subadult, and mature plants), indicating that mature plants do not exert significant inhibitory effects on the growth of young individuals. In high-density areas, the population exhibited a distribution radiating outward from mature plants as the center, with high-density cores predominantly concentrated within 0 to 5 m. Significant density variations were observed between regions, with the highest total density estimated at approximately 9.57 plants m−2 and the lowest at 2.68 plants m−2. The invasion mechanism of S. chamaejasme is closely associated with the spatial independence of its age groups and a distribution pattern dominated by subadult plants. During the initial invasion phase, S. chamaejasme spreads predominantly around mature plants. After securing sufficient growing space (0 to 1 m), it further competes for territory through shifts in distribution patterns—transitioning from aggregated to random distribution. Additionally, significant differences in distribution density and expansion patterns across regions provide critical theoretical foundations for targeted ecological management strategies.

The troublesome weed Johnsongrass [Sorghum halepense (L.) Pers.] is predicted to expand its range under climate change. In the process, it is likely to become more competitive in corn (Zea mays L.) production areas of the northeastern United States and southern Canada. A replicated greenhouse experiment was conducted to measure interspecific and intraspecific competition between an S. halepense biotype from central New York State (northern range edge) and corn under drought and well-watered conditions. Drought stress significantly reduced the biomass and height of corn and S. halepense in both rounds of the experiment (P < 0.001). Drought stress increased the root-to-shoot ratio of S. halepense (P < 0.001) and reduced the root-to-shoot ratio of corn (P < 0.001). In one run of the experiment, corn produced 19.3% more aboveground biomass (P < 0.001) and 6.6% more height (P < 0.001) when competing with an S. halepense plant (interspecific competition) than when competing with a second corn plant (intraspecific competition). Drought conditions increased the advantage of corn plants grown under interspecific relative to intraspecific competition (P = 0.012). In that round of the experiment, biomass of S. halepense was 12.9% higher under intraspecific competition than interspecific competition in the well-watered treatment and 15.5% higher under intraspecific competition than interspecific competition in the drought treatment (main effect of competition, P = 0.002). Differences between competition treatments were smaller in the other round of the experiment (P > 0.05). Our findings suggest that the New York S. halepense biotype used in this study may not be as competitive as biotypes found in this weed’s range core in more southern regions of the United States. However, anticipated effects of climate change may increase the abundance and competitiveness of this species in the northeastern United States.

Italian ryegrass [Lolium perenne L. ssp. multiflorum (Lam.) Husnot], a pernicious weed in wheat (Triticum aestivum L.) fields, has evolved severe resistance to the acetolactate synthase (ALS)-inhibiting herbicides, like pyroxsulam. Here, the derived cleaved amplified polymorphic sequence (dCAPS) markers were developed to detect two distinct mutations at the 197th position of the ALS gene. The method was used to examine and purify the resistant population. Homozygous populations with different 197 site mutations from the same population were obtained, and the target site–resistance mechanisms were investigated. Whole-plant dose–response bioassays show that the resistance index (RI) of the Pro-197-Thr mutant population to pyroxsulam was 508.92, whereas that of the Pro-197-Gln population was 9.75. Similar trends were observed for different herbicides within same mode of action. In vitro ALS assays demonstrated that the Pro-197-Thr population exhibited lower sensitivity to pyroxsulam than the Pro-197-Gln population, consistent with plant bioassays. Furthermore, ALS gene expression of the Pro-197-Thr population analysis is significantly higher than that in the Pro-197-Gln population, which may also explain why the Pro-197-Thr population exhibits a higher resistance level than the Pro-197-Gln population. Our findings suggest that different amino acid substitutions at one ALS gene locus can confer herbicide resistance with different levels in L. perenne ssp. multiflorum. This study provides valuable insights into the mechanisms of herbicide resistance in L. perenne ssp. multiflorum.

Precision weed detection and mapping in vegetable crops are beneficial for improving the effectiveness of weed control. This study proposes a novel method for indirect weed detection and mapping using a detection network based on the You-Only-Look-Once-v8 (YOLOv8) architecture. This approach detects weeds by first identifying vegetables and then segmenting weeds from the background using image processing techniques. Subsequently, weed mapping was established and innovative path planning algorithms were implemented to optimize actuator trajectories along the shortest possible path. Experimental results demonstrated significant improvements in both precision and computational efficiency compared with the original YOLOv8 network. The mean average precision at 0.5 (mAP50) increased by 0.2, while the number of parameters, giga floating-point operations per second (GFLOPS), and model size decreased by 0.57 million, 1.8 GFLOPS, and 1.1 MB, respectively, highlighting enhanced accuracy and reduced computational costs. Among the analyzed path planning algorithms, including Christofides, Dijkstra, and dynamic programming (DP), the Dijkstra algorithm was the most efficient, producing the shortest path for guiding the weeding system. This method enhances the robustness and adaptability of weed detection by eliminating the need to detect diverse weed species. By integrating precision weed mapping and efficient path planning, mechanical actuators can target weed-infested areas with optimal precision. This approach offers a scalable solution that can be adapted to other precision weeding applications.

A series of laboratory experiments were conducted to break seed dormancy and to investigate the germination ecology of prostrate knotweed (Polygonum aviculare L.) populations for designing weed management practices in eastern Australia. Foundational studies identified sodium hypochlorite (NaOCl) immersion of seeds for 8 h as the most effective method for breaking seed dormancy and enhancing germination. Therefore, in the subsequent seed germination ecology experiments, seeds treated with NaOCl for 8 h followed by a 10-min water rinse were used, and two populations (Gatton and Nangwee) were selected for the studies. The Gatton population exhibited higher germination than the Nangwee population at alternating day/night temperatures ranging from 15/5 to 30/20 C. Germination in both populations did not vary at day/night temperatures ranging from 20/10 C to 30/20 C. Therefore, considering P. aviculare as a winter-season weed in Australia, an optimal temperature of 20/10 C was selected for further light/dark, salt and osmotic stress, residue cover, and burial depth studies. Averaged over populations, germination of P. aviculare peaked at 92% under alternating light/dark conditions but declined to 49% in complete darkness, confirming the species’ positive photoblastic nature. Under stress (salt and osmotic) conditions, the Gatton population maintained ∼50% germination at 250 mM NaCl and −0.8 MPa osmotic potential and showed higher tolerance to these stresses than the Nangwee population. Moderate residue cover (2 to 4 Mg ha⁻¹) enhanced seedling emergence (up to 58% in Nangwee and 36% in Gatton), likely due to improved surface moisture and partial light availability. However, seed burial beyond 4 cm nearly eliminated emergence due to light exclusion and mechanical resistance. These findings suggest that P. aviculare is well adapted to surface soil conditions and may thrive in reduced-tillage, residue-retained systems. Strategic deep tillage and surface-targeted herbicides are essential for effective management of this light-sensitive, residue-adapted weed.

Tomato (Solanum lycopersicum L.) is extremely sensitive to inhibitors of acetohydroxyacid synthase (AHAS; also known as acetolactate synthase [ALS]). Utilizing ethyl methanesulfonate mutagenesis of seeds of the commercial tomato line ‘M82’, we developed a tomato mutant, HRT1, that showed high resistance to imidazolinone herbicides (which act by inhibiting AHAS) in the greenhouse and under field conditions. The activity of AHAS extracted from HRT1 was significantly less affected by imidazolinone herbicides than that from the parental line M82. Following imazapic treatment, no differences were found in the content of free branched-chain amino acids in HRT1 tissues as compared to a dramatic decrease in M82 tissues. No differences were found in the susceptibility of AHAS to sulfonylurea herbicides. A single point transition mutation of C to T in the AHAS1 gene located on chromosome 3 was detected. This mutation resulted in substitution of alanine by valine at amino acid position 194, corresponding to 205-Alal in Arabidopsis. Ligand–protein contact analysis showed that replacement of alanine by the larger hydrophobic valine residue results in increased repulsion, hindering herbicide binding. Segregation analysis indicated that the resistance to imidazolinones in line HRT1 is due to a single recessive gene.

Drought-tolerant (DT) corn (Zea mays L.) hybrids are developed to provide crop protection from plant water stress in areas prone to drought like the Intermountain West. These regions also face challenges from weeds because of the wide range of developmental and physiological mechanisms possessed by weeds that give an ecological advantage under increased temperature and water stress. Many weeds have developed resistance to some herbicides; therefore, understanding weed interactions with DT corn is important in developing sustainable strategies for management in water-stressed environments. A two-season field experiment was conducted to evaluate the critical period of weed control (CPWC) in DT versus drought-susceptible (DS) corn hybrids exposed to optimal and reduced irrigation in Utah. Treatment combinations of the two corn hybrids, two irrigation levels, and time of weed removal were arranged in a split-split plot design with each treatment replicated four times. Exponential decay and asymptotic regression models were used to determine the CPWC based on an estimated 5% relative yield loss in corn. Up to 5% and 42% yield differences were observed between weed-free and weedy plots throughout the 2021 and 2022 field seasons, respectively. The beginning and end of CPWC differed between the two corn hybrids as well as between the two irrigation levels in both seasons. CPWC was 19.5 and 28 d for DT corn under optimal irrigation in 2021 and 2022, respectively. CPWC was increased for DS corn with optimal irrigation to 52 and 35 d in 2021 and 2022, respectively. A similar result was observed with reduced irrigation for each hybrid (5 and 48.5 d for DT corn and 35 and 50 d for DS corn in 2021 and 2022, respectively). The results suggest that use of DT corn may help reduce the need for more intensive weed management because it reduces the CPWC.