Herbicide-resistant Weeds Research Articles

Molecular Mechanisms of Resistance against PSII-Inhibiting Herbicides in Amaranthus retroflexus from the Czech Republic.

Amaranthus retroflexus L. (redroot pigweed) is one of the most problematic weeds in maize, sugar beet, vegetables, and soybean crop fields in Europe. Two pigweed amaranth biotypes (R1 and R2) from the Czech Republic resistant to photosystem II (PSII)-inhibiting herbicides were analyzed in this study. This study aimed to identify the genetic mechanisms that underlie the resistance observed in the biotypes. Additionally, we also intended to establish the use of chlorophyll fluorescence measurement as a rapid and reliable method for confirming herbicide resistance in this weed species. Both biotypes analyzed showed high resistance factors in a dose-response study and were thus confirmed to be resistant to PSII-inhibiting herbicides. A sequence analysis of the D1 protein revealed a well-known Ser-Gly substitution at amino acid position 264 in both biotypes. Molecular docking studies, along with the wild-type and mutant D1 protein's secondary structure analyses, revealed that the S264G mutation did not reduce herbicide affinity but instead indirectly affected the interaction between the target protein and the herbicides. The current study identified the S264G mutation as being responsible for conferring herbicide resistance in the pigweed amaranth biotypes. These findings can provide a strong basis for future studies that might use protein structure and mutation-based approaches to gain further insights into the detailed mechanisms of resistance in this weed species. In many individuals from both biotypes, resistance at a very early stage (BBCH10) of plants was demonstrated several hours after the application of the active ingredients by the chlorophyll fluorescence method. The effective PS II quantum yield parameter can be used as a rapid diagnostic tool for distinguishing between sensitive and resistant plants on an individual level. This method can be useful for identifying herbicide-resistant weed biotypes in the field, which can help farmers and weed management practitioners develop more effective weed control tactics.

Screening the Potential f Fungal Derived Bioherbicide in Weed Management

Synthetic herbicides have long been a cornerstone of modern agriculture, providing effective weed control but often at significant environmental and health costs. These chemicals can persist in the environment, leach into groundwater, and harm non-target organisms, including humans. Additionally, the overuse of synthetic herbicides has led to the development of herbicide-resistant weeds, further complicating weed management strategies. In response to these challenges, researchers and farmers alike are increasingly turning to bioherbicides derived from fungi as a sustainable alternative. Fungal bioherbicides harness the natural antagonistic properties of fungi to target weeds. Unlike synthetic herbicides, which are chemically synthesized and often broad-spectrum in action, fungal bioherbicides utilize either the fungi themselves as pathogens or their metabolites to disrupt weed growth. This approach offers several distinct advantages:Target Specificity: Fungal bioherbicides can be highly specific to certain weed species or even to specific stages of weed growth. This specificity reduces collateral damage to non-target plants and organisms, making them particularly suitable for environmentally sensitive areas such as organic farms, riparian zones, and protected ecosystems. Environmental Friendliness: Unlike synthetic herbicides that can persist in the environment and accumulate in soil and water bodies, fungal bioherbicides generally have lower persistence. They degrade more rapidly and often have minimal impact on non-target organisms, thereby preserving biodiversity and ecosystem health. Reduced Risk of Resistance: Synthetic herbicides often face the challenge of herbicide-resistant weeds, which evolve due to continuous and widespread use. Fungal bioherbicides, by contrast, pose a lower risk of resistance development. This is because they typically act through multiple modes of action or biochemical pathways within the weed, making it harder for weeds to develop resistance mechanisms. Research into fungal-derived bioherbicides is actively exploring and harnessing these advantages. Scientists are screening diverse fungal species to identify potent pathogens or metabolites that effectively inhibit weed growth. Moreover, advances in biotechnology and genetic engineering allow for the enhancement of fungal strains to optimize their bioherbicidal properties while ensuring safety and efficacy. One promising example is the use of fungal pathogens like Phomamacrostoma and Colletotrichum truncatum, which have demonstrated efficacy against various weed species including common agricultural weeds like velvetleaf and pigweed. These fungi infect weeds through mechanisms such as spore attachment, penetration of plant tissues, and secretion of phytotoxic metabolites that inhibit weed growth. In addition to their direct impact on weed management, fungal bioherbicides contribute to sustainable agricultural practices by reducing reliance on synthetic chemicals. They align with principles of integrated pest management (IPM) by offering a biological control method that complements cultural and mechanical weed control strategies. Moving forward, continued research and development efforts are essential to refine fungal bioherbicides, optimize application techniques, and expand their practical use in diverse agricultural settings. Challenges such as formulation stability, cost-effectiveness, and regulatory approvals also need to be addressed to facilitate widespread adoption by farmers.

Optimizing molecular assays for glyphosate and ALS-inhibitor resistance diagnostics in four weed species

Herbicide-resistant weeds pose a threat to food production in modern agriculture, causing US$32 billion in crop production losses worldwide. In Michigan, highly troublesome and widespread weeds include waterhemp, Palmer amaranth, common ragweed, and horseweed, with accessions that are resistant to glyphosate (Group 9) and ALS-inhibitors (Group 2), major herbicide sites of action utilized in soybean and corn cropping systems. Molecular assays for rapid resistance diagnostics to confirm the in-field status of herbicide resistance can assist with more effective, timely, and proactive management. In this research, we developed and tested PCR-based assays to identify target site resistance mechanisms to both herbicide groups through Sanger sequencing and EPSPS copy number variation. Nine different SNPs were identified in five ALS positions known to confer herbicide resistance among all species surveyed. Pro197Ser was the most frequent in horseweed and common ragweed accessions, whereas Trp574Leu was the predominant mutation in Palmer amaranth and waterhemp. Four horseweed accessions contained the Pro106Ser mutation in the EPSPS gene, which confers resistance to glyphosate. Additionally, waterhemp and Palmer amaranth had 2–7 and 20–160 copies of EPSPS, respectively. The assays were validated by comparing genotyping of several field-collected accessions of unknown resistance status with known resistant and susceptible accessions. The efficacy of genotyping assays was >98% and required only two days, confirming that molecular assays are a robust tool for rapid resistance diagnostics. These assays can help growers evaluate herbicide resistance status in weed populations within the same growing season, allowing them to adopt effective management practices.

Herbicides in modern sustainable agriculture: environmental fate, ecological implications, and human health concerns

AbstractHerbicides play a crucial role in modern agriculture by controlling weeds and ensuring sustainable crop productivity. However, the use of herbicides has raised concerns regarding their contamination, posing serious threat to the environment, biodiversity, and food safety. Recent trends indicate a decline in the overall volume of herbicides usage, suggesting a shift towards more specific and targeted formulations of herbicides. Also, there has been an increased use of systemic and pre-emergence herbicides. The global agriculture still faces several challenges because of the adverse environmental impacts caused by herbicide contamination, both at the application site and offsite. In view of the growing concern, it is necessary to develop new herbicides with greater selectivity or bio-based herbicide that can degrade after successful control of the intended weed population and minimize or eliminate the environmental hazards. Furthermore, the adoption of integrated weed management practices rather than prolonged and repeated use of herbicide in agriculture can effectively reduce the growth of herbicide-resistant weed populations. The present review is a single valuable resource, providing insights into the recent trends and future challenges associated with herbicide use in modern agriculture, with a focus on human health and food safety. Also, we emphasize the advancements in herbicide technology, emergence of new herbicide-resistant weed species, regulatory considerations, and alternative approaches in herbicide use, all of which are particularly valuable to agroecology, policymakers, and stakeholders. Graphical Abstract

Early detection and management of herbicide resistant weeds

Small weed patches may be noticed in fields after herbicide application, but they typically do not have a significant impact on the season’s crop yield. As a result, they are usually not treated as a threat to future yields. However, if these patches harbour weed biotypes resistant to one or multiple herbicides, resistance alleles can spread both spatially (via various dispersal pathways, including seed transport by machinery and commodity contamination) and temporally (through seed persistence). This poses a significant threat to herbicide-based weed management. Once these populations spread and cover a large enough area, eradication becomes improbable despite all the resistance management efforts. Therefore, a proactive and collaborative endeavour is needed to detect and manage small and patchy resistant weed populations. In this paper we review the current potential of weed resistance detection using imagery and molecular markers as well as possible weed management approaches. Finally, we advocate for the use of a combination of these techniques to manage herbicide resistant weeds when populations are small. This multifaceted approach is presently not applicable to all resistance mechanisms, and all weed species located in any crop, but could initially focus on biotypes and species that are easy to detect and represent the greatest threat.

Laser weeding of common weed species

The massive use of herbicides since the 1950s has resulted in increasing problems with herbicideresistant weeds and pollution of the environment, including food, feed, and water. These side effects have resulted in political pressures to reduce herbicide application. The European Commission aims to reduce the use and risk of chemicals and more hazardous pesticides in the EU. Therefore, new weed control methods are in demand. Laser weeding might be an alternative to replace or supplement herbicides and other weed control methods in an Integrated Weed Management (IPM) strategy. This work aimed to investigate how increasing laser energy affected common weeds when the apical meristem was exposed to irradiation at the early stages of development. A 50 W thulium-doped fibre laser with a diameter of 2 mm and a wavelength of 2 µm was used. The highest efficacy of laser irradiation was achieved when the grass weed (Alopecurus myosuroides) had one leaf and the dicot species were at the cotyledon stage. There was a large difference between the species’ susceptibility to irradiation probably caused by differences in morphology and growth habit. At the 4-leaf stage, most of the species regrew after irradiation. Laser weeding may be a solution to replace or supplement other weed control methods in some crops, but in general the weeds must be irradiated when they are at the cotyledon to 2-leaf stage to avoid regrowth.

Distribution, frequency, and impact of herbicide-resistant weeds in Saskatchewan

Herbicide-resistant weeds threaten contemporary agriculture by reducing crop yields and quality. Monitoring of herbicide-resistant weeds is essential to the development of informed integrated weed management (IWM) strategies. In 2019 and 2020, a randomized-stratified preharvest survey of 419 fields in Saskatchewan, Canada, was conducted to determine the distribution, frequency of occurrence, and impact of herbicide-resistant weeds. Mature seeds were collected from uncontrolled weeds in each field. The samples were tested for resistance to acetyl-CoA carboxylase (ACCase) and/or acetolactate synthase (ALS)-inhibiting herbicides using whole-plant bioassays under a controlled-environment. In 2019/2020, herbicide-resistant weeds occupied 72% of the surveyed fields, corresponding to an estimated 6.2 million ha of annual cropland and a total field area of 11.4 million ha. Herbicide-resistant weeds cost Saskatchewan farmers an estimated $343 million CAD annually in reduced crop yields and quality, and increased weed control expenditures. Wild oat ( Avena fatua L.) had the greatest impact among grass weeds, with ACCase inhibitor resistance documented in 77% and ALS inhibitor resistance in 30% of fields where the weed seeds were collected and tested (47% and 18% of all fields surveyed, respectively). Multiple herbicide (ACCase and ALS inhibitor)-resistant wild oat were documented in 26% of the tested fields. Kochia ( Bassia scoparia (L.) A.J. Scott) had the greatest impact among broadleaf weeds, where 100% of the samples tested were ALS inhibitor-resistant (39% of all fields surveyed). The growing prevalence of herbicide-resistant weeds in Saskatchewan warrants further adoption of IWM where non-chemical tactics play an important role in stewardship of the remaining effective herbicides.

IMPACT OF SOIL STERILIZATION FROM DIFFERENT LOCATIONS, WHEAT SEEDS CLEANING AND THEIR INTERACTIONS ON WEED CONTROL, AND YIELD AND YIELD COMPONENTS

IMPACT OF SOIL STERILIZATION FROM DIFFERENT LOCATIONS, WHEAT SEEDS CLEANING AND THEIR INTERACTIONS ON WEED CONTROL, AND YIELD AND YIELD COMPONENTS

Two-Pass Weed Management Programs for Identity-Preserved Soybean

Weed management is a challenge in Identity-Preserved (IP) soybean in Ontario, Canada. Six experiments were established in southwestern Ontario, Canada during 2021 and 2022 to evaluate weed control and soybean yield with preemergence (PRE), early postemergence (EPOST), and PRE followed by (fb) late POST (LPOST) herbicide programs. At 8 weeks after LPOST herbicide applications, S-metolachlor/metribuzin, pyroxasulfone/sulfentrazone, and flumioxazin/metribuzin/imazethapyr applied PRE provided 7, 49, and 99% control of velvetleaf; 65, 98, and 100% control of green pigweed; 7, 8, and 82% control of common ragweed; 25, 68, and 98% control of common lambsquarters; 91, 77, and 89% control of barnyardgrass; and 62, 68, and 93% control of green foxtail, respectively. Imazethapyr + bentazon applied EPOST provided 91% control of velvetleaf; 91% control of green pigweed; 78% control of common ragweed; 95% control of common lambsquarters; 76% control of barnyardgrass; and 79% control of green foxtail. S-metolachlor/metribuzin, pyroxasulfone/sulfentrazone, and flumioxazin/metribuzin/imazethapyr applied PRE fb bentazon + fomesafen + quizalofop applied LPOST provided 61, 86, and 100% control of velvetleaf; 97, 99, and 100% control of green pigweed; 94, 88, and 99% control of common ragweed; 96, 98, and 100% control of common lambsquarters; 97, 95, and 97% control of barnyardgrass; and 97, 96, and 99% control of green foxtail, respectively. There was minimal and transient soybean injury (6% or less) with all PRE or EPOST herbicide treatments, however, S-metolachlor/metribuzin, pyroxasulfone/sulfentrazone, or flumioxazin/metribuzin/imazethapyr applied PRE fb bentazon + fomesafen + quizalofop LPOST caused up to 22% injury in soybean. Weed interference reduced soybean yield 40%. Weed interference with S-metolachlor/metribuzin and pyroxasulfone/sulfentrazone applied PRE reduced soybean yield 25 and 31%, respectively. Reduced weed interference with flumioxazin/metribuzin/imazethapyr applied PRE, imazethapyr + bentazon applied EPOST, and the two-pass programs of a PRE fb LPOST herbicide resulted in soybean yield that was similar to the weed-free control. This study concludes that there are many effective weed management programs in IP soybean; however, the two-pass weed control programs are recommended since they provide good to excellent weed control, minimize soybean yield loss from weed interference, and ensure the use of multiple herbicide modes of action which reduces the selection intensity for the evolution of herbicide-resistant weeds.

Assessment of Allelopathic Potential of Cotton Chromosome Substitution Lines.

Weed interference consistently poses a significant agronomic challenge in cotton production, leading to unfavorable direct and indirect consequences. Consequently, the predominant strategy employed to manage weeds is the application of synthetic herbicides. However, this extensive reliance has resulted in the development of herbicide-resistant weed populations due to the prolonged use of a single herbicide and the lack of rotation. This project focused on identifying weed-suppressive cotton chromosome substitution (CS) lines. These CS lines closely resemble the parent TM-1, an upland cotton derivative (Gossypium hirsutum). Each CS line carries a single chromosome or chromosome arm exchanged from G. barbadense, G. tomentosum, or G. mustelinum within the TM-1 background. In a greenhouse experiment utilizing a stepwise approach, five CS lines, along with two conventional varieties (Enlist and UA48) and the parent line (TM1), were assessed to determine their potential for suppressing Palmer amaranth growth. The plant height was measured 7, 14, and 21 days after establishment, and the chlorophyll content was measured 21 days after establishment. The results revealed varying levels of chlorophyll reduction in Palmer amaranth, with the Enlist variety displaying the lowest reduction (32%) and TM-1 exhibiting the highest (78%). Within 14 days of establishment, the CS lines T26lo, BNTN 1-15, and T11sh demonstrated substantial suppression of Palmer amaranth height, with reductions of 79, 70, and 71%, respectively. Conversely, Enlist displayed the least effective performance among the CS lines. Moreover, CS22, CS49, CS50, CS34, UA48, and CS23 displayed a decreasing trend in reducing Palmer amaranth height from 14 to 21 days after establishment. This research demonstrates the inherent herbicidal attributes within cotton CS lines against Palmer amaranth. In light of the versatile applications of cotton fibers and the unique characteristics of the G. hirsutum genome, this study investigates the potential of specific cotton lines in enhancing weed management practices. By elucidating the implications of our findings, we aim to contribute to promoting sustainability and developing alternatives to synthetic herbicides in agricultural systems.

Cropping system typologies perform differently under climate stress in Manitoba, Canada: multi-criteria assessment

Information is required to understand how novel biodiversity strategies can improve cropping system resilience to climate change. A “business as usual” (BAU) rotation (wheat–canola–wheat–soybean) was compared with a “warm-season crop” (WS) rotation (corn–sunflower–dry bean–canola); a “biodiverse” (BD) rotation (fall rye with cover crop– corn/soybean intercrop—pea/canola intercrop–green fallow mixture); a “perennial grain” (Kernza) rotation (Kernza grain intermediate wheatgrass); and an organic (ORG) rotation (millet-green fallow mixture-wheat). Drought conditions prevailed in both study years. The BAU rotation had the lowest average yield (1821 kg ha−1 compared with 2533 and 3083 kg ha−1 for the BD and WS rotations, respectively), less post-harvest residual biomass, and a lower net return than the WS rotation. The WS rotation was limited by herbicide-resistant weeds in dry beans. Kernza seed yield was five times lower than for spring wheat. ORG wheat yielded the same as other wheat and had a higher net return. Live roots days, a measure of soil health potential, were 95 for the BAU rotation and 174 and 113 for the BD and WS rotations, respectively; the most were recorded for Kernza (365). Seasonal crop growth duration was increased by including Kernza and fall rye for early season growth, and corn, sunflower, a corn–soybean intercrop, a cover crop, and fall-seeded rye for late season growth. WS and BD rotations outperformed the BAU rotation and the BD system accomplished this with half the N fertilizer. Results demonstrate the potential of biodiverse rotations; barriers to their adoption should be addressed.

Low-concentration repeated exposure and high-concentration single exposure of cyanamide suppressed the growth of redroot pigweed in the alfalfa field

The inclination toward natural products has led to the onset of the discovery of new bioactive metabolites that could be targeted for specific therapeutic or agronomic applications. Despite increasing knowledge coming to light of plant-derived materials as leads for new herbicides, relatively little is known about the mode of action on herbicide-resistant weeds. Cyanamide (CA) is a naturally occurring herbicide synthesized by hairy vetch (Vicia villosa Roth.). However, it has not been experimentally verified whether CA suppresses target plants via sustained discharge at low concentrations, as is often the case with most plant-derived materials. This study aimed to detect the toxicity and the mode of action of CA to alfalfa (Medicago sativa L.) and redroot pigweed (Amaranthus retroflexus L.). The toxicity of CA toward the alfalfa and redroot pigweed by three different exposure patterns was compared: low-concentration repeated exposure with 0.3 g/L CA (LRE), high-concentration single exposure with 1.2 g/L CA (HSE), and distilled water spray as control. The results showed that CA had a stronger inhibitory effect on redroot pigweed growth compared to alfalfa under both LRE and HSE exposure modes, with leaves gradually turning yellow and finally wilting. Beyond that, field trials were conducted to corroborate the toxicity of CA to alfalfa and redroot pigweed. The results have also shown that CA could inhibit the growth of redroot pigweed without significant adverse effects on alfalfa. The outcomes concerning electrolyte permeability, root activity, and malondialdehyde (MDA) content indicated that CA suppressed the growth of redroot pigweed by interfering with the structure of the cell membrane and impacting cellular osmotic potential. CA could destroy the cell membrane structure to inhibit the growth of the redroot pigweed by both LRE and HSE exposure modes, which provides a theoretical basis for preventing and controlling redroot pigweed in alfalfa fields.

Comparison of Straw Mulching and Herbicide Levels for Control of Various Weed Species in Maize (Zea mays L.)

Weed management in maize is one of biggest concerns for growers. To reduce dependence on chemicals and chances of herbicide resistant weeds, and to improve soil status, thus straw mulching was added as cultural component with chemicals for improving weed management in maize. Field experiments were conducted at two locations (Punjab Agricultural University, Ludhiana, and Regional Research Station, Gurdaspur) during kharif season to find out the influence of different paddy straw mulch and herbicides for control of various weeds species in maize. The results showed that application of paddy straw mulch 6.25 t/ha effectively controlled Eleusine indica, Cynodon dactylon, Commelina benghalensis, Eragrostis tenella, Digitaria sanguinalis, Echinochloa colona, Trianthema portulacastrum, Portulaca oleracea, Phyllanthus niruri, Euphorbia hirta, Conyza stricta and Cyperus compressus over no mulching. In addition to above weed species, paddy straw mulch 9.0 t/ha also effectively reduced density of Dactyloctenium aegyptium, Acrachne racemosa, Digera arvensis, Mollugo nudicaulis, Alternanthera philoxeroides, Amaranthus viridis and Veronica agrestis and Cyperus rotundus as compared to 6.25 t/ha and no mulch treatment. Atrazine pre emergence at 1.0 kg/ha controlled Eleusine indica, Echinochloa crusgalli, Eragrostis tenella, Digitaria sanguinalis, Echinochloa colona, Trianthema portulacastrum, Mollugo nudicaulis, Alternanthera philoxeroides, Digera arvensis, Amaranthus viridis and Cyperus compressus compared to its lower dose (0.8 kg/ha) and control at all stages. Post emergence application of tembotrione reduced the density of all weed species compared to atrazine and unweeded control.

Short-term immunotoxicity induced by florpyrauxifen-benzyl herbicide exposure in the spleen of male albino mice.

Florpyrauxifen-benzyl (FPB)is a new arylpicolinate systemic herbicide that has been used to control or suppress the majority of herbicide-resistant biotype weeds in rice. To our knowledge, the impact of FPB on the immune system remains undetected thus far. Hence, this work aimed to address the toxic effects of FPB and the possible related mechanisms on the spleen of exposed mice. Initially, an acute toxicological test was performed to ascertain the median lethal dose (LD50) of FPB for 24 h which was found to be 371.54 mg/kg b.wt. For mechanistic evaluation of FPB toxicity, three sublethal doses (1/20th, 1/10th, and 1/5thLD50) were orally administered to mice for 21 consecutive days. Changes in spleen relative weight, oxidative status, apoptotic and inflammatory markers, histopathological alterations were evaluated. Following the FPB exposure, significant (p < 0.05) decline in spleen index, apoptotic features, histolopathological changes were observed. Additionally, excessive oxidative stress in spleen tissues was monitored by downregulating antioxidant enzymes and upregulating the oxidant parameters. Furthermore, exposure to FPB resulted in notable activation of the NF-қB signaling pathway, accompanied by elevated levels of pro-inflammatory cytokines (namely, IL-1βand TNF-α)as well as CD3 and CD19 levels have decreased significantly in spleen tissues. Collectively, FPB exposure exhibited apoptosis, oxidative stress, immunosuppression, and inflammatory response in a dose-dependent manner, leading to spleen tissue damage and immunotoxicity. Further studies on FPB is recommended to outstand its hazards on ecosystems.

Assessing the Use of Butachlor 5G in High and Mid Altitude Rice Growing Areas in Bhutan: A Case Study

Rice is a vital cereal crop in Bhutan, cultivated widely for domestic consumption. Rice production is gradually decreasing due to diverse reasons including labour shortages and insufficient irrigation water. With the shortage of farm labour, weed management is challenging and Bhutanese farmers have long relied on Butachlor 5G for weed control. However, prolonged use of a single herbicide can lead to herbicide resistance in weeds. This study aimed to determine the extent of use of the weedicide and to assess the development of Butachlor resistance in paddy weeds through farmers’ perceptions. The study, conducted in four western rice-growing areas, surveyed 190 farmers using semi-structured questionnaires. The findings revealed that Butachlor has been extensively used for over three decades, with most farmers applying it more than the recommended dosage. Despite this, 86.85% of respondents reported a decrease in Butachlor's effectiveness over the years. More than half of the respondent (50.53%) believed that weeds had developed resistance to Butachlor, a concern that correlated with the increased dosage used. The findings suggest a diminishing efficacy of Butachlor, potentially attributed to the development of herbicide resistance. Of significance, the study identifies Potamogeton distinctus as the most prevalent weed, followed by Schoenoplectiella juncoides and Pontederia vaginalis in the surveyed areas.

Palmer amaranth (Amaranthus palmeri S. Wats.) and waterhemp (Amaranthus tuberculatus (Moq.) J.D. Sauer) biovigilance in Canadian Agro-ecosystems

The evolution and spread of herbicide-resistant weeds threatens long-term sustainability of Canadian agro-ecosystems. Herbicide-resistant weeds increase management inputs and costs, increase off-target and environmental exposure to pesticides, reduce yield quality and quantity, and impede harvest efficiency. Amaranthus species including Palmer amaranth ( Amaranthus palmeri S. Wats.) and waterhemp ( Amaranthus tuberculatus (Moq.) J.D. Sauer) are particularly concerning due to both their propensity towards herbicide resistance evolution, their history of invasion, and their spread in agro-ecosystems. A biovigilance approach is taken to build awareness of these pigweeds' initial invasion and spread in the USA. Characteristics of their identification, potential hybridization, and known herbicide resistance evolution are reviewed. Fourteen species of Amaranthus are found in Canada, nine of which (including waterhemp) possess herbicide-resistant biotypes. A total of 45 hybrids between various Canadian Amaranthus species with each other or Palmer amaranth have been noted. Hybrids have been experimentally produced or observed from herbarium specimens, with three cases of herbicide resistance transfer notably with Palmer amaranth or waterhemp. Mitigation strategies will depend on successful species identification and herbicide resistance status determination. Common pathways for Palmer amaranth introductions in the northern USA include both animal feed systems with grain screenings and crop production systems including seed and equipment contamination. Regional awareness campaigns will be critical to support Canadian farmers in identifying and quickly mitigating invasions of Palmer amaranth and waterhemp to prevent establishment and spread of infestations into new areas.

The effectiveness of isopropylamine glyphosate 486 g/L + metsulfuron methyl 1 g/L herbicidal combination in oil palm (Elaeis guineensis)

Lack of knowledge in weed control techniques in oil palm cultivation practices can lead to decreased productivity. One of the herbicides that can be used to control weeds in oil palm cultivation is a mixed herbicide made from isopropylamine glyphosate 486 g/L and methyl metsulfuron 1 g/L. The use of mixed herbicides with two or more active ingredients can broaden the spectrum of weed control, reduce herbicide residues, slow the emergence of herbicide-resistant weeds, and reduce production costs. Therefore, this study aims to determine the effectiveness of mixed herbicides IPA glyphosate 486 g/L and methyl metsulfuron 1 g/L in controlling weeds in oil palm plants in the producing phase. This research was conducted at Bukit Nyomot oil palm plantation Subang Regency, Jawa Barat Province from February to May 2023. The experimental design used was Randomized Complete Block Design (RCBD) with 6 treatments and each treatment was replicate 4 times. The treatments are consisted of the application of mixed herbicides IPA glyphosate 486 g/L and methyl metsulfuron 1 g/L at doses of 1 L/ha; 1.5 L/ha; 2 L/ha; 2.5 L/ha; manual weeding; and control (no treatment). The results shows that the mixed herbicide IPA glyphosate 486 g/L and methyl metsulfuron 1 g/L at a dose of 1 L/ha to 2.5 l/ha is effective in controlling weeds in oil palm, such as Paspalum conjugatum, Ottochloa nodosa, Asystasia intrusa, Ageratum conyzoides, Chromolaena odorata, other weeds, and total weeds up to 12 Weeks After Application (WAA).

The mechanism behind tenuazonic acid-mediated inhibition of plant plasma membrane H+-ATPase and plant growth

The Increasing prevalence of herbicide-resistant weeds has led to a search for new herbicides that target plant growth processes differing from those targeted by current herbicides. In recent years, some studies have explored the use of natural compounds from microorganisms as potential new herbicides. We previously demonstrated that tenuazonic acid (TeA) from the phytopathogenic fungus Stemphylium loti inhibits the plant plasma membrane (PM) H+-ATPase, representing a new target for herbicides. In this study, we further investigated the mechanism by which TeA inhibits PM H+-ATPase and the effect of the toxin on plant growth using Arabidopsis thaliana. We also studied the biochemical effects of TeA on the PM H+-ATPases from spinach (Spinacia oleracea) and A. thaliana (AHA2) by examining PM H+-ATPase activity under different conditions and in different mutants. Treatment with 200 μM TeA induced cell necrosis in larger plants, and treatment with 10 μM TeA almost completely inhibited cell elongation and root growth in seedlings. We show that the isoleucine backbone of TeA is essential for inhibiting the ATPase activity of the PM H+-ATPase. Additionally, this inhibition depends on the C-terminal domain of AHA2, and TeA binding to PM H+-ATPase requires the Regulatory Region I of the C-terminal domain in AHA2. TeA likely has a higher binding affinity towards PM H+-ATPase than the phytotoxin fusicoccin. Finally, our findings show that TeA retains the H+-ATPase in an inhibited state, suggesting that it could act as a lead compound for creating new herbicides targeting the PM H+-ATPase.

A first survey for herbicide resistant weeds across major maize growing areas in the North Island of New Zealand.

Weeds are increasingly documented with evolved resistance to herbicides globally. Three species have been reported as resistant in maize crops in New Zealand: Chenopodium album to atrazine and dicamba, Persicaria maculosa to atrazine and Digitaria sanguinalis to nicosulfuron. Despite knowledge of these cases, the distribution of these resistant biotypes is unknown. This study aimed to determine the prevalence of known resistant weeds in major maize growing areas in New Zealand, and to pro-actively screen other species for resistance. Weed seeds of broadleaf and grass species were collected from 70 randomly selected maize growing farms in the North Island in 2021-2022. Seeds were grown and treated with herbicides at recommended field rates. Atrazine-resistant C. album were recorded in a third of surveyed farms and nicosulfuron-resistant D. sanguinalis in a sixth. Half of Waikato farms and a quarter of Bay of Plenty farms (no Hawkes Bay or Wellington farms) had atrazine-resistant C. album. Dicamba-resistant C. album were not detected, nor were atrazine-resistant P. maculosa. Nicosulfuron resistant D. sanguinalis was recorded in 19% of Waikato farms, 6% of Bay of Plenty farms and 9% of Hawkes Bay farms (no Wellington farms). Amaranthus spp., Fallopia convolvulus, Persicaria spp., Solanum spp., Echinochloa crus-galli, Panicum spp. and Setaria spp. were not resistant to any of the herbicides tested. Twenty-nine to 52% of maize farms in the North Island are estimated to have herbicide resistant weeds. Resistance is common in maize farms in Waikato and western Bay of Plenty. Resistance is rare in southern regions, with only one instance of nicosulfuron-resistant D. sanguinalis and no resistant C. album. Most annual weeds in maize are not resistant to herbicides; although atrazine resistant C. album is widespread, it is currently controlled with alternative herbicides. Resistant D. sanguinalis appears to be an emerging problem.

Exploring sterile pollen technique as a novel tool for management of Palmer amaranth (Amaranthus palmeri)

AbstractThe success of the insect sterile technique (IST) in managing insect pests raised the hypothesis that a similar approach could be employed to control weed populations. Here, we investigated the feasibility of employing irradiated sterile pollen as a means to disrupt seed production in dioecious weeds, specifically focusing on Palmer amaranth (Amaranthus palmeri S. Watson). Our goal was to determine the optimal irradiation dose that strikes a balance between inducing sterility and preserving competitiveness, as excessive doses could result in pollen mortality, while low doses may retain fertility. Plants were grown in a greenhouse during the summer of 2020 and spring of 2021. Once they reached the flowering stage, male and female individuals were isolated. Mature pollen samples were collected and exposed to varying dosages (0, 100, 200, 300, 400, and 500 Gy) of gamma rays. These irradiated and non-irradiated pollen samples were used in pollen viability assessments and hand-pollination experiments. In the hand-pollination study conducted in 2020, we employed six pollination treatments using different irradiation doses. The results showed that 300 Gy was the most effective dose, resulting in a maximum reduction of 30% in seed set compared with open pollination when irradiated pollen had prior access to the stigma through artificial pollination before open pollination. In 2021, to simulate real field conditions, three additional treatments were introduced into the study, further confirming the effectiveness of the optimal 300 Gy dose. Our findings indicate that the sterile pollen technique (SPT) using irradiated pollen can be a valuable approach for reducing weed seed production. SPT also holds potential for broad-spectrum weed control by mixing sterile pollen from multiple weed species in a single application. Additionally, it could aid in managing herbicide-resistant weeds that have survived in-season control efforts. This research contributes to the development of novel and sustainable weed management strategies.