Grass Weeds Research Articles

Growth and fecundity of Palmer amaranth escaping glufosinate in soybean with and without grass competition

Abstract Field experiments were conducted at Clayton and Rocky Mount, North Carolina, during the summer of 2020 to determine the growth and fecundity of Palmer amaranth plants that survived glufosinate with and without grass competition in soybean crops. Glufosinate (590 g ai ha−1) was applied at early postemergence (when Palmer amaranth plants were 5 cm tall), mid-postemergence (7–10 cm), and late postemergence (>10 cm) and at orthogonal combinations of those timings. Nontreated Palmer amaranth was grown in weedy (i.e., intraspecific and grass competition), weed-free in-crop (WFIC), and weed-free fallow (WFNC) conditions for comparisons. No Palmer amaranth plants survived the sequential glufosinate applications and control decreased as the plants were treated at a larger size in both experiments. The apical and circumferential growth rate of Palmer amaranth surviving glufosinate was reduced by more than 44% compared with the WFNC Palmer amaranth. The biomass of Palmer amaranth plants that survived glufosinate was reduced by more than 87% compared with the WFNC Palmer amaranth. The fecundity of Palmer amaranth that survived glufosinate was reduced by more than 70% compared with WFNC Palmer amaranth. Palmer amaranth plants that survived glufosinate were as fecund as the WFIC Palmer amaranth in both experiments in soybean fields. The results prove that despite the significant vegetative growth rate decrease of Palmer amaranth that survived glufosinate, plants can be as fecund as nontreated plants. The trends in growth and fecundity of Palmer amaranth that survives glufosinate with and without grass competition were similar. These results suggest that glufosinate-treated grass weeds may not reduce the growth or fecundity of Palmer amaranth that survives glufosinate.

Application technology for bioherbicides: challenges and opportunities with dry inoculum and liquid spray formulations.

Bioherbicides offer many potential benefits as part of an integrated weed management system or a totally biological or organic cropping system. A key factor for success is the selection of appropriate formulation and delivery systems for each target weed and cropping/climatic region. For dry inoculum products, we discuss direct implantation as an example for successful control of woody weeds, with benefits in control extending beyond the treated weeds to surrounding weeds. These applications do not require water and will become less labor-intensive with future robotic application platforms. Indeed, all bioherbicide applications are likely to improve and become more cost-effective with the advance of new application platforms with sensors and targeted control at lower application volume rates. Unmanned aerial vehicles, as new application platforms, are one of several such potential progressive application systems for liquid formulations, and we discuss product design to maintain optimum conditioning of the active ingredient(s) and storage stability. The delivery system must not adversely affect the products and the application volume rate must be appropriate for coverage on the target. Where applied with other products, compatibility must be ensured and appropriate mixing orders observed to assure performance and avoid precipitation or settling. Droplet size is important for allowing the active materials to be included in the spray, which may require droplets with diameter >150 μm for some larger particle biologically active agents. However, droplet size should not be too large to achieve target coverage. In some cases, that may be plant stems rather than leaves, or narrow grass weeds which tend to have highest spray collection efficiency for small droplets. Narrow droplet size spectrum nozzles may help optimize droplet size. We propose spray calculators to help optimize performance for coverage, retention and avoidance of drift losses, bounce, shatter and runoff. These include regulatory-supported, validated models. © 2023 The Authors. Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

A systematic review of chemical weed management in peanut (Arachis hypogaea) in the United States: challenges and opportunities

AbstractHerbicides are the primary tool for controlling weeds in peanut (Arachis hypogaea L.) and are crucial to sustainable peanut production in the United States. The literature on chemical weed management in peanut in the past 53 yr (1970 to 2022) in the United States was systematically reviewed to highlight the strengths and weaknesses of different herbicides and identify current research gaps in chemical weed management. Residual weed control in peanut is achieved mainly with dimethenamid-P, ethalfluralin, pendimethalin, and S-metolachlor. More recently, the use of the protoporphyrinogen oxidase inhibitor flumioxazin and acetolactate synthase inhibitors, such as diclosulam, for residual weed control in peanut has increased considerably. Postemergence broadleaf weed control in peanut is achieved mainly with acifluorfen, bentazon, diclosulam, imazapic, lactofen, paraquat, and 2,4-DB, while the graminicides clethodim and sethoxydim are the major postemergence grass weed control herbicides in peanut. Although several herbicides are available for weed control in peanut, no single herbicide can provide season-long weed control due to limited application timing, lack of extended residual activity, variability in weed control spectrum, and rotational restrictions. Therefore, effective weed management in peanut often requires herbicide mixtures and/or sequential application of preplant-incorporated, preemergence, and/or postemergence herbicides. However, the available literature showed a substantive range in herbicide efficacy due to variations in environmental conditions and flushes of weed germination across years and locations. Despite the relatively high efficacy of herbicides, the selection of herbicide-resistant weeds is another area of increasing concern. Future research should focus on developing new strategies for preventing or delaying the development of resistance and improving herbicide efficacy within the context of climate change and emerging constraints such as water shortages, rising temperatures, and increasing CO2 concentration.

Repeated evolution of herbicide resistance in Lolium multiflorum revealed by haplotype-resolved analysis of acetyl-CoA carboxylase.

Herbicide resistance in weeds is one of the greatest challenges in modern food production. The grass species Lolium multiflorum is an excellent model species to investigate evolution under similar selection pressure because populations have repeatedly evolved resistance to many herbicides, utilizing a multitude of mechanisms to neutralize herbicide damage. In this work, we investigated the gene that encodes acetyl-CoA carboxylase (ACCase), the target site of the most successful herbicide group available for grass weed control. We sampled L. multiflorum populations from agricultural fields with history of intense herbicide use, and studied their response to three ACCase-inhibiting herbicides. To elucidate the mechanisms of herbicide resistance and the genetic relationship among populations, we resolved the haplotypes of 97 resistant and susceptible individuals by sequencing ACCase amplicons using long-read DNA sequencing technologies. Our dose-response data indicated the existence of many, often unpredictable, resistance patterns to ACCase-inhibiting herbicides, where populations exhibited as much as 37-fold reduction in herbicide response. The majority of the populations exhibited resistance to all three herbicides studied. Phylogenetic and molecular genetic analyses revealed multiple evolutionary origins of resistance-endowing ACCase haplotypes, as well as widespread admixture in the region regardless of cropping system. The amplicons generated were diverse, with haplotypes exhibiting 26-110 polymorphisms. Polymorphisms included insertions and deletions 1-31 bp in length, none of which were associated with the resistance phenotype based on an association analysis. We also found evidence that some populations have multiple mechanisms of resistance. Our results highlight the astounding genetic diversity in L. multiflorum populations, and the potential for repeated evolution of herbicide resistance across the landscape that challenges weed management approaches and jeopardizes sustainable weed control practices. We provide an in-depth discussion of the evolutionary and practical implications of our results.

Investigating image-based fallow weed detection performance on Raphanus sativus and Avena sativa at speeds up to 30 km h−1

Site-specific weed control (SSWC) can provide considerable reductions in weed control costs and herbicide usage. Despite the promise of machine vision for SSWC systems and the importance of ground speed in weed control efficacy, there has been little investigation of the role of ground speed and camera characteristics on weed detection performance. Here, we compare the performance of four camera/software combinations using the open-source OpenWeedLocator platform – (1) default settings on a Raspberry Pi HQ camera (HQ1); (2) optimised software settings on a HQ camera (HQ2), (3) optimised software settings on the Raspberry Pi v2 camera (V2); and (4) a global shutter Arducam AR0234 camera (ARD) – at speeds ranging from 5 km h−1 to 30 km h−1. A combined excess green (ExG) and hue, saturation, value (HSV) thresholding algorithm was used for testing under fallow conditions using tillage radish (Raphanus sativus) and forage oats (Avena sativa) as representative broadleaf and grass weeds, respectively. ARD demonstrated the highest recall among camera systems, with up to 100 % recall for tillage radish and 91.6 % for forage oats at 5 km h−1. At 30 km h−1 ARD recall for forage oats declined (P < 0.05) by 12.4 %. There was no significant change for tillage radish. All cameras experienced a decrease in recall as speed increased. The highest rate of decrease was observed for HQ1 with 1.12 % and 0.90 % reductions in recall for every km/h increase in speed for tillage radish and forage oats, respectively. Detection of the ‘grassy’ forage oats was worse (P < 0.05) than the broadleaved tillage radish for all cameras. Despite the variations in recall, HQ1, HQ2, and V2 maintained near-perfect precision at all tested speeds. The variable effect of ground speed and camera system on detection performance of grass and broadleaf weeds, indicates that careful hardware and software considerations must be made when developing SSWC systems.

Predicitng yield of irrigated red clover (Trifolium pratense L.) pastures in response to temperature.

Two datasets from red clover monoculture pastures grown in Lincoln, New Zealand, were analysed to generate coefficients to predict red clover yield. The mean annual production of established red clover was 17.0±0.48 t DM/ha, with a maximum mean growth rate of 125±9.36 kg DM/ha/day (spring Year 2). In the establishment year irrigated red clover grew at a constant rate of 7.30±0.14 kg DM/ha/°Cd (Tb = 3 °C) throughout the year. In contrast, there was a splitline linear response in Years 2 and 3, which differed between years and decreased after the second week of January. Specifically, the growth rate in Phase 1 was 7.70±0.38 kg DM/ha/°Cd in Year 2, which was 16% higher than the 6.60±0.28 kg DM/ha/oCd in Year 3. The difference probably reflected increased competition from weed grasses as red clover content declined from &gt;95% to ~75% of total annual yield. After January, red clover grew at 3.05±0.35 kg DM/ha/°Cd, in both years. This lower rate occurred in the mid-January-July period, and probably reflected a change in partitioning of assimilate to red clover roots in response to a decreasing photoperiod. The coefficients reported here for red clover need to be validated from other datasets. However, they provide easily transferable coefficients that can be used to estimate red clover yield under nonlimiting conditions for other locations. These could be integrated into feed budgeting software to assist onfarm decision making.

First Report on Resistance to HPPD Herbicides Mediated by Nontarget-Site Mechanisms in the Grass Leptochloa chinensis.

The emergence of 4-hydroxyphenylpyruvate dioxygenase (HPPD) herbicides as efficacious target-site herbicides has been noteworthy. In recent years, only four species of broadleaf weeds have developed resistance due to the long-term widespread use of HPPD herbicides. This study represents the first reported instance of a grass weed exhibiting resistance to HPPD inhibitors. We identified a new HPPD-resistant Chinese sprangletop [Leptochloa chinensis (L.) Nees] population (R population). At the recommended dose of tripyrasulfone, the inhibition rate of the R population was only half that of the sensitive population (S). The mechanism underlying resistance does not involve target-site resistance triggered by amino acid mutations or depend on disparities within the HPPD INHIBITOR SENSITIVE 1 (HIS1) gene. The impetus for resistance appears to be interlinked with the metabolic activities of cytochrome P450 monooxygenase (P450) and glutathione S-transferase (GST) family genes. Following RNA sequencing (RNA-seq) and quantitative real-time PCR (qRT-PCR) validation, the study suggests that five P450 genes, CYP71C1, CYP74A2, CYP72A1, CYP84A1, and CYP714C2, alongside a single GST gene GSTF1, may be implicated in the process of metabolic detoxification.

Invasion by Cenchrus spinifex changes the soil microbial community structure in a sandy grassland ecosystem

Continuous nitrogen deposition increases the nitrogen content of terrestrial ecosystems and alters the soil nitrogen cycling process. Invasive plants have strong environmental adaptability, which can not only affect the composition and diversity of soil microbial community but also significantly affect the transformation process of soil nitrogen, leading to successful invasion. Currently, research on invasive plant soil ecosystems mainly focused on changes in soil nutrients and soil microorganisms. As an invasive annual grass weed with strong ecological adaptability, the impact of Cenchrus spinifex at different growth periods on soil environment and soil microbial structure composition and diversity in sandy grassland ecosystems is still unclear. In this study, soil samples were collected from four habitats with different degrees of invasion in situ during the vegetation and reproductive growth periods of Cenchrus spinifex. High-throughput sequencing and qPCR technology were used to analyze the changes in the composition, structure and diversity characteristics of the soil microbial communities during Cenchrus spinifex invasion. The results indicated that Cenchrus spinifex invasion had different effects on the soil environment at different growth periods, and Cenchrus spinifex had a preference for the utilization of ammonium nitrogen during vegetation growth period. Moreover, Cenchrus spinifex invasion significantly changed the composition and structure of soil bacterial communities, and the response of soil bacterial and fungal communities to the invasion was inconsistent. Additionally, the bacterial network was more stable than the fungal network. At different growth periods, Cenchrus spinifex had a significant impact on the key microbial communities of soil nitrogen cycling. The invasion increased the abundance of nifH and AOA-amoA, while decreased the abundance of AOA-amoB. Alkaline hydrolyzed nitrogen, total nitrogen and total phosphorus content were key factors that affect vegetation growth period and change the key microbial communities of nitrogen cycling. Alkaline hydrolyzed nitrogen, total phosphorus and organic carbon were key factors in reproductive growth period that alter the nitrogen cycling of key microbial communities.

Mitochondrial and Proteasome Dysfunction Occurs in the Hearts of Mice Treated with Triazine Herbicide Prometryn.

Prometryn is a methylthio-s-triazine herbicide used to control the growth of annual broadleaf and grass weeds in many cultivated plants. Significant traces of prometryn are documented in the environment, mainly in waters, soil, and plants used for human and domestic consumption. Previous studies have shown that triazine herbicides have carcinogenic potential in humans. However, there is limited information about the effects of prometryn on the cardiac system in the literature, or the mechanisms and signaling pathways underlying any potential cytotoxic effects are not known. It is important to understand the possible effects of exogenous compounds such as prometryn on the heart. To determine the mechanisms and signaling pathways affected by prometryn (185 mg/kg every 48 h for seven days), we performed proteomic profiling of male mice heart with quantitative liquid chromatography-tandem mass spectrometry (LC-MS/MS) using ten-plex tandem mass tag (TMT) labeling. The data suggest that several major pathways, including energy metabolism, protein degradation, fatty acid metabolism, calcium signaling, and antioxidant defense system were altered in the hearts of prometryn-treated mice. Proteasome and immunoproteasome activity assays and expression levels showed proteasome dysfunction in the hearts of prometryn-treated mice. The results suggest that prometryn induced changes in mitochondrial function and various signaling pathways within the heart, particularly affecting stress-related responses.

Effect of Class Act NG Adjuvant on Glyphosate Efficacy in Corn

There is little information on the effect of the co-application of glyphosate with Class Act NG adjuvant on weed control efficacy and corn yield under Ontario environmental conditions. This study consisted of 6 field experiments that were conducted in Ontario during 2021 and 2022 to determine if the addition of Class Act NG (2.5% v/v) to glyphosate at 450, 900 and 1350 g ae ha-1 would improve weed control and result in a concomitant increase in corn yield. The co-application of glyphosate with Class Act NG resulted in no visible corn injury at 1 and 4 weeks after herbicide application (WAA). The addition of Class Act NG to glyphosate at 450 g ae ha-1 improved control of common lambsquarters, velvetleaf, Powell amaranth, common ragweed, and barnyardgrass as much as 20, 14, 9, 8, and 7%, respectively but there was no improvement in control of giant foxtail, or green foxtail and there was no increase in corn yield. The addition of Class Act NG to glyphosate at 900 g ae ha-1 improved common lambsquarters control 6 and 5% at 4 and 8 WAA, respectively and improved barnyardgrass control 4% at 4 WAA. The addition of Class Act NG to glyphosate at 1350 g ae ha-1 provided no improvement in control of velvetleaf, Powell amaranth, common ragweed, common lambsquarters, barnyardgrass, giant foxtail, or green foxtail and there was no increase in corn yield. Based on this data the co-application of glyphosate with Class Act NG results in improved control of some annual broadleaf and grass weeds (common lambsquarters, velvetleaf, Powell amaranth, common ragweed and barnyardgrass) when glyphosate is applied at 450 or 900 g ae ha-1; however, when glyphosate is applied at 1350 g ae ha-1 there was no improvement in weed control. The addition of Class Act NG to glyphosate at 450, 900 and 1350 g ae ha-1 did not result in an increase in corn yield.

Evaluation of two‐pass herbicide programs for broad‐spectrum weed control in conventional tillage non‐transgenic corn production in Wisconsin atrazine prohibition areas

AbstractAchieving effective weed control is crucial for Wisconsin conventional corn growers farming in atrazine prohibition areas. Upon request from our extension clientele, a field study was conducted at Arlington and Brooklyn, WI, in 2021 and 2022 (four site‐years). The study aimed to evaluate the weed control efficacy of comprehensive two‐pass (PRE followed by POST) herbicide program treatments containing products with a wide range of active ingredients and sites of action from various manufacturers without atrazine and glyphosate, in conventional tillage non‐transgenic corn production. Nine and eight out of the 11 two‐pass herbicide programs investigated provided &gt;90% giant foxtail (Setaria faberi Herrm), common ragweed (Ambrosia artemisiifolia L.), velvetleaf (Abutilon theophrasti Medik) and waterhemp [Amaranthus tuberculatus (Moq.) J.D. Sauer] control in 2021, respectively. However, only three treatments provided &gt;90% waterhemp control and the greatest giant foxtail control in 2022 was 79%. Greater end‐of‐season broadleaf and grass weed control was observed in 2021 compared to 2022 due to lower weed pressure and timely early‐season rainfall in 2021. The two‐pass programs, acetochlor/mesotrione fb dicamba/tembotrione (94%–100%) and acetochlor/flumetsulan/clopyralid fb nicosulfuron + dicamba/diflufenzopyr (85%–100%), provided the most consistent broadleaf control across all site‐years. These results demonstrate that a well‐designed and timely deployed two‐pass herbicide program can provide effective control of common broadleaf and grass weeds in conventional corn production assuming moderate weed pressure and timely rainfall for soil residual herbicide activation, otherwise effective weed control, particularly of grass weeds, in the absence of atrazine and glyphosate can be challenging. These results are also translatable to support weed management decisions for glyphosate‐resistant corn hybrids in non‐atrazine prohibition areas.

DIVERSITY OF WEED SPECIES IN COCOA PLANTATIONS IN BANYUWANGI, EAST JAVA, INDONESIA

Cocoa (Theobroma cacao L.) is one of the important plantation commodities in Indonesia. However, one of the factors that can affect productivity is weeds because weeds compete with cocoa in getting water, sunlight, nutrients, air, and space to grow. One of the largest cocoa plantation areas in East Java is the Banyuwangi district. Information about the types of cocoa weeds in Banyuwangi is unknown even though weeds in one area are different from another. Weed can reduce the production of cocoa. So, This study is important for determining appropriate control methods. This study aimed to determine the type, diversity, and abundance of weeds. The research method used in this study was a survey with a square-plot size. All weed samples were identified. The results showed that there were twelve types of broadleaf weeds, three types of grass weeds, one type of sedge, and one type of fern. The highest importance value index (IVI) was found in Ottochloa nodosa at 40.91%. The diversity of weeds was in a medium category. Weed diversity in cocoa plantations in Banyuwangi was different from other areas in Indonesia. The results of this research contribute to providing information on the diversity of weeds that can be used in determining weed control strategies in cocoa plantations.

A Study in Scaffold Hopping: Discovery and Optimization of Thiazolopyridines as Potent Herbicides That Inhibit Acyl-ACP Thioesterase.

In the search for new chemical entities that can control resistant weeds by addressing novel modes of action (MoAs), we were interested in further exploring a compound class that contained a 1,8-naphthyridine core. By leveraging scaffold hopping methodologies, we were able to discover the new thiazolopyridine compound class that act as potent herbicidal molecules. Further biochemical investigations allowed us to identify that the thiazolopyridines inhibit acyl-acyl carrier protein (ACP) thioesterase (FAT), with this being further confirmed via an X-ray cocrystal structure. Greenhouse trials revealed that the thiazolopyridines display excellent control of grass weed species in pre-emergence application coupled with dose response windows that enable partial selectivity in certain crops.

Control Efficacy of Natural Products on Broadleaf and Grass Weeds Using Various Application Methods

Synthetic herbicides have negatively impacted biological organisms and human health. Thus, nonsynthetic herbicides for weed control are needed in organic and conventional agriculture. Nonsynthetic products such as vinegar and detergents are increasingly becoming popular in crop disease treatment, as well as controlling insects and weeds. Therefore, the objective of this study was to determine the herbicidal efficacy of various nonsynthetic products using different application methods. Various nonsynthetic products were applied to grass and broadleaf weeds at 1%, 3%, 5%, and 10% concentrations to test their herbicidal efficacy, and two plant extracts were used as adjuvants. In addition, the inhibitory effects of selected brown rice vinegar and effective microorganisms (EM) powder soap on grass and broadleaf weeds were compared to the inhibitory effects of other vinegars and EM powder soaps. Of the nine various natural products tested, brown rice vinegar and EM powder soap at 5% concentrations were the only applications to completely control grass and broadleaf weeds in Petri dish bioassays. In greenhouse conditions, the shoot fresh weight of Eclipta prostrata, Solanum nigrum, Persicaria hydropier, and Portulaca oleracea was completely inhibited when soil applications of EM powder soap at 10% concentrations were used. EM powder soap was more effective in controlling grass and broadleaf weeds than brown rice vinegar. In addition, brown rice vinegar and EM powder soap did not appear to last long in soil. Two-time application methods were more effective in controlling all weed species than one-time application methods. However, no synergism effects were observed when brown rice vinegar and EM powder soap were combined with other natural products. Brown rice vinegar and EM powder soap did not show adjuvant effects when combined with plant extracts, which can sometimes create better contact with or penetration of the weeds. Thus, weeds growing alongside transplanted vegetable crops can be effectively controlled with brown rice vinegar and EM powder soap by using soil applications in row, either individually or combined together and with either one or two applications.

Tumble windmill grass (Chloris verticillata Nutt.) control with POST herbicides

AbstractTumble windmill grass (Chloris verticillata Nutt.) is a problematic perennial grass weed in the semiarid Central Great Plains (CGP). Greenhouse and fallow field experiments were conducted during 2021 and 2022 at Kansas State University Agricultural Research Center near Hays, KS, to determine the effectiveness of various POST herbicides for tumble windmill grass control. All selected POST herbicides were applied at field‐recommended rates at the seedling growth stage (3‐to 4‐inches tall) of tumble windmill grass in greenhouse study. Tumble windmill grass was at the heading growth stage (10‐to‐12‐inches tall) in fallow fields when POST herbicides were tested. Results from greenhouse study indicated that quizalofop‐P‐ethyl (QPE) and clethodim provided ≥ 95% control and shoot biomass reduction of tumble windmill grass at 28 days after treatment. Glyphosate provided 89% control and 93% shoot biomass reduction of tumble windmill grass. Imazamox and nicosulfuron had the least control (41 to 51%) and shoot biomass reduction (43 to 66%) of tumble windmill grass in greenhouse study. In contrast, all tested POST herbicides were comparatively less effective on tumble windmill grass (≤68% control and ≤ 50% shoot biomass reduction) except glyphosate (85% control and 54% shoot biomass reduction) in field study. These results conclude that clethodim, QPE, and glyphosate applied at early growth stages can provide effective control of tumble windmill grass in the CGP region.

Characterization of imazamox-resistant shattercane (Sorghum bicolor L.) populations from Kansas

AbstractShattercane is a problematic summer annual grass weed species in regions that produce grain sorghum. Three shattercane populations (DC8, GH4, and PL8) collected from sorghum fields from northwestern Kansas survived the field-use rate (52 g ha−1) of postemergence-applied imazamox. The main objectives of this research were to 1) confirm and characterize the level of resistance to imazamox in putative imazamox-resistant (IMI-R) shattercane populations, 2) investigate the underlying mechanism of resistance, and 3) determine the effectiveness of postemergence herbicides for controlling IMI-R populations. A previously known imazamox susceptible (SUS) shattercane population from Rooks County, KS, was used. All three putative populations exhibited a 4.1-fold to 6.0-fold resistance to imazamox compared with the SUS population. The ALS gene sequences from all IMI-R populations did not reveal any known target-site resistance mutations. A pretreatment with malathion, which inhibits cytochrome P450, followed by imazamox at various doses, reversed the resistance phenotype of the PL8 population. In a separate greenhouse study, postemergence treatments with nicosulfuron, quizalofop, clethodim, and glyphosate resulted in ≥96% injury to all IMI-R populations. The lack of known ALS target-site mutations and the reversal of resistance phenotype by malathion suggest the possibility of metabolism-based resistance to imazamox in PL8 shattercane population.

Herbicide Resistance in Summer Annual Weeds of Australia’s Northern Grains Region

For more than two decades, glyphosate has been relied on to control summer annual weeds in fallow systems in Australia’s northern grains region. With numerous cases of glyphosate resistance reported in weed species collected from this region, there are concerns about the future viability of this herbicide. A random seed collection survey of summer weeds was conducted between 2016 and 2018 with the aim of determining the frequency and distribution of resistance to glyphosate and other herbicides commonly used for summer weed control. Glyphosate resistance was ubiquitous in fleabane, with all collected populations resistant to this herbicide. Glyphosate resistance was also prevalent in feathertop Rhodes grass, windmill grass, and awnless barnyard grass, with resistance detected in 68%, 58%, and 36% of populations, respectively. Only 14% of sowthistle populations collected between 2013 and 2108 were resistant to glyphosate. Resistance to haloxyfop was detected in feathertop Rhodes grass, albeit at a low frequency (2%). Other herbicides, such as 2,4-D amine, propaquizafop, and clethodim, provided good control of the broadleaf and grass weeds tested. The results from these surveys conducted between 2013 and 2017 provide a first glimpse of the state of herbicide resistance in key crop weeds for Queensland and the northern region of New South Wales. It is clear that farmers and agronomists need to consider incorporating non-chemical weed management tactics to promote the sustainability of current herbicides.

Evaluation of Bipolaris yamadae as a bioherbicidal agent against grass weeds in arable crops.

Weeds are among the most damaging pests of agriculture, causing ≈10% worldwide reduction in crop productivity each year. Over-reliance on synthetic chemical herbicides has caused weeds around the world to evolve resistance. Bioherbicides may be an alternative. However, among their many constraints including strict environmental requirements, complicated mass-production and high product costs, limited pathogenicity and a narrow spectrum of activity are frequently encountered and are major barriers to commercialization. We isolated a pathogenic fungus, HXDC-1-2, from diseased leaves of a gramineous weed, stiltgrass [Microstegium vimineum (Trin.) A. Camus], from the edge of farmland in Guizhou province, China. HXDC-1-2 was identified as the fungal species Bipolaris yamadae based on the morphological characteristics and ITS-GPDH-EF1α multiple primer analysis. Its potential as a bioherbicide was evaluated by determining its weed control efficacy and crop safety. The ED50 and ED90 values of HXDC-1-2 on Echinochloa crus-galli were 3.22 × 103 and 1.32 × 105 conidia mL-1 , respectively. Host range tests revealed that 20 gramineous weeds including Setaria viridis, Leptochloa chinensis, Eleusine indica, Pseudosorghum zollingeri, Leptochloa panicea, Bromus catharticus, E. crus-galli plants, were extremely susceptible whereas 77 crop species from 27 plant families including rice, wheat, barley, corn, soybean and cotton (excluding cowpea and sorghum) were unaffected. Bipolaris yamadae strain HXDC-1-2 has great potential to be developed as a commercial broad-spectrum bioherbicidal agent for controlling grass weeds in arable crops. © 2023 Society of Chemical Industry.

Isolation and Identification of Herbicidal Active Compounds from Brassica oleracea L. and Exploration of the Binding Sites of Brassicanate A Sulfoxide.

Brassica oleracea L. has strong allelopathic effects on weeds. However, the allelochemicals with herbicidal activity in B. oleracea L. are still unknown. In this study, we evaluated the activity of allelochemicals isolated from Brassica oleracea L. based on the germination and growth of model plant Lactuca sativa Linn., grass weed Panicum miliaceum, and broadleaf weed Chenopodium album. Additionally, we employed molecular docking to predict the binding of brassicanate A sulfoxide to herbicide targets. The results of this study showed that eight compounds with herbicidal activity were isolated from B. oleracea L., and the predicted results indicated that brassicanate A sulfoxide was stably bound to dihydroxyacid dehydratase, hydroxymethylpyruvate dioxygenase, acetolactate synthase, PYL family proteins and transport inhibitor response 1. This research provides compound sources and a theoretical foundation for the development of natural herbicides.

Effect of dew and spray volume on the efficacy of control of asulam on fall panicum (Panicum dichotomiflorum)

Asulam controls fall panicum (Panicum dichotomiflorum Michx.), the most troublesome annual grass weed in Florida sugarcane. This study was conducted to evaluate the effect of dew on asulam efficacy on fall panicum control when applied using different spray volumes. Fall panicum 30 cm tall with 0, 50, and 100% dew on leaves equivalent to no dew, moderate dew, and heavy dew, respectively, were treated with asulam at 3,700 g ha–1 using spray volumes of 94, 140, 187, and 281 L ha–1. Fall panicum control was rated 28 days after treatment, and aboveground biomass was harvested immediately. The presence or absence of dew and spray volume did not significantly influence asulam efficacy on fall panicum control and aboveground biomass accumulation. Fall panicum was controlled from 89% to 94% at the different dew levels and spray volumes. Heavy dew did not diminish the performance of asulam. The presence of dew on fall panicum foliage probably hydrated the cuticle and aided water-soluble asulam to remain in solution for a longer period, thereby enhancing uptake. The water-holding capacity of fall panicum foliage with the heavy dew and spray volumes was probably not exceeded, resulting in no runoff and no subsequent reduction of control. These results indicate that dew deposition under Florida conditions has no effect on asulam efficacy on fall panicum 30 cm tall or less when applied at commonly used spray volumes of 140 and 187 L ha–1.