Resistant Weeds Research Articles

Germination Characteristics Associated With Glutathione S-Transferases Endowed Quizalofop-p-Ethyl Resistance in Polypogon fugax

Quantification of germination characteristics between herbicide-resistant and -susceptible weeds might provide methods to control resistant weeds and permit better prediction of evolution and persistence of herbicide resistance. This study aimed to compare the germination characteristics of Asian minor bluegrass (Polypogon fugax) populations that are resistant or susceptible to quizalofop-p-ethyl under controlled conditions, which the resistance mechanism is involved in glutathione S-transferases (GSTs) metabolism-based resistance. No major differences in seed germination were found at diverse temperatures, pH ranges, and light conditions. However, a significant difference that seed response to a gradient of osmotic and salt stress between the resistant and susceptible P. fugax populations were found. Two stress response genes (P5CS-1 and CDPK-2) in P. fugax were likely involved in germination rate as well as germination speed in response to these stresses. Subsequently, population verification demonstrated that P5CS-1 and CDPK-2 genes may be linked to the resistance mechanism. Additionally, the two genes play an important role in response to salt stress and osmotic stress as shown by transcript abundance after stress treatments. Our findings suggest that the variation of the germination characteristics in P. fugax associates with the presence of GST-endowed resistance mechanism.

Surveying stakeholder’s perception of glufosinate and use in North Carolina

AbstractGlufosinate is among the few remaining effective herbicides for postemergence weed control in North Carolina crops. The evolution of glufosinate resistance in key weeds is currently not widespread in North Carolina, but to better assess the current status of glufosinate effectiveness, surveys were distributed at Extension meetings in 2019 and 2020. The surveys were designed to provide information about North Carolina farmers’ perception of glufosinate and its use. Survey results indicate that many North Carolina farmers (≥26%) apply glufosinate at the correct timing (5- to 10-cm weeds). In addition, North Carolina farmers (≥22%) are applying glufosinate as a complementary herbicide to other efficacious herbicides and to control herbicide-resistant weeds, suggesting that glufosinate is part of a diverse chemical weed management plan. Conversely, survey findings indicated that some farmers (13% to 17%) rely exclusively on glufosinate for weed control. Additionally, 28% to 30% of farmers reported glufosinate control failures, and control failures were observed on several weed species among corn, cotton, and soybean crops. The results of the survey suggest that most North Carolina farmers are currently stewarding glufosinate, but they also support the need for Extension personnel to keep educating farmers on how to correctly use glufosinate to delay the evolution of glufosinate-resistant weeds. Semiannual surveys should be distributed to monitor where glufosinate control failures occur and the weed species not being controlled.

Increasing the competitiveness of vegetable crops to weeds by improving control methods

Weeds are a major threat in crop production, and controlling them in modern agriculture is critical to preventing crop losses and ensuring food security. Intensive farming practices, climate change and natural disasters affect weed dynamics, requiring a change in management practices. Existing methods are no longer viable due to lack of manpower; chemical control methods are limited by health hazards and the development of herbicide resistance in weeds. This article discusses some potential alternative weed control strategies in modern vegetable production that are feasible and effective. Increasing the competitiveness of vegetable crops through proper planning of agrotechnologies system, preventive, cultural and mechanical methods, development of competitive varieties, allelopathy, biological control and reduction of weed seed production at harvest will be a major aspect in sustainable weed management. Improving tillage regimes has long been considered the main measure of weed control. Control of weed seed production and weed injuriousness have been shown as potential tools to reduce weed seed germination and retention in the soil. The development of allelopathy has led to the emergence of new methods of weed control. The use of the allelopathic potential of crops also deserves mention in modern weed control methods. Thermal weed control is seen as a useful method. The role of bioherbicides as an integral part of sustainable weed management is emphasized. All of these strategies are viable for modern agriculture; however, choosing a specific method and using the right combinations will be the key to success. No strategy is perfect, and therefore an integrated approach can provide the best results. The adoption of such practices can improve the efficiency of farming systems in sustainable agricul- ture. A comprehensive method for protecting vegetable crops from weeds and ways to reduce the potential contamination of fields with seeds and weed seedlings are described. The optimal norms and technological features, conditions for the effective use of modern herbicides on crops and plantings of vegetable crops are given.

Comparison between the mechanisms of Clearfield ® wheat and Lolium rigidum multiple resistant to acetyl CoA carboxylase and acetolactate synthase inhibitors

Clearfield® wheat (Triticum aestivum) have helped eliminate the toughest grasses and broadleaf weeds in Spain since 2005. This crop production system includes other tolerant cultivars to the application of imidazolinone (IMI) herbicides. However, the continuous use and off-label rates of IMI herbicides can contribute to the development of resistance in Lolium rigidum and other weed species. In this research, the main objectives were to study the resistance mechanisms to acetolactate synthase (ALS) and acetyl coenzyme A carboxylase (ACCase) inhibitors in a L. rigidum accession (LrR) from a Clearfield® wheat field, with a long history rotating these IMI-tolerant crops and compare them with those present in the IMI-tolerant wheat. The resistance to ACCase inhibitors in LrR was due to point mutations (Ile1781Leu plus Asp2078Gly) of the target site gene plus an enhanced herbicide metabolism (EHM), on the other hand, in wheat accessions was due only by EHM. Mechanisms involved in the resistance to ALS inhibitors were both point mutations of the target gene and EHM in the IMI-tolerant wheat, while only evidence of mutation (Trp574Leu) was found in the multiple herbicide resistant L. rigidum accession. This research demonstrates that if crop rotation is not accompanied by the use of alternative sites of action in herbicide-tolerant crops, resistant weeds to herbicide to which crops are tolerant, can easily be selected. Moreover, repeated and inappropriate use of Clearfield® crops and herbicide rotations can lead to the evolution of multiple resistant weeds, as shown in this study, and have also inestimable environmental impacts.

Weed Management Practices in Wheat (Triticum aestivum L.): A Review

Wheat is India’s second-largest staple food crop grown in different agro climatic zones within different crop sequences, as a result of which a diversity of weeds infests to this crop. Diversity of weeds including grassy, broadleaf weeds and sedges are mainly infested to the crop. Phalaris minor (grassy) and Rumex dentatus (broadleaf) are the most dominant weeds in northern region of country. For receiving fast results, use of herbicides is most popular method of weed control and used all over the world. But over reliance on herbicides has created several complications such as environmental quality deterioration, shifting in weed flora and development of herbicide resistant weeds. These problems can be abridged to a great extent by decreasing reliance on chemical method which can be done by integration of various cultural and mechanical methods to the weed management program. Various cultural practices such as nutrient management, seeding rate, spacing, cropping sequence, water management, sowing methods, sowing time and competitive varieties should be followed in such a way that crop plants utilize much more resources in comparison to weed plants. As a mechanical measure, Furrow Irrigated Raised Bed (FIRB) method and stale seed bed technique are recommended for effective weed management. Timely application of herbicides with recommended doses with the help of efficient spray technology improves the efficacy of herbicides. So with the help of Integrated Weed Management (IWM) i.e integration of various cultural, mechanical and chemical methods, we can efficiently managed the diverse weed flora in wheat crop.

Arkansas Rice: Herbicide Resistance Concerns, Production Practices, and Weed Management Costs

An online survey to better understand current weed management practices and concerns in Arkansas rice was distributed in the fall of 2020. A total of 123 respondents from across the Arkansas rice growing region returned the survey covering a total of 236,414 rice hectares, representing about 40% of the planted Arkansas rice hectares in 2020. The most problematic weeds were Echinochloa crus-galli (L.) P. Beauv. (ECG), Cyperus spp., and Oryza sativa L. (weedy rice), respectively, in flooded rice, and ECG, Amaranthus palmeri S. Wats., and Cyperus spp., respectively, in furrow-irrigated rice. Most respondents (78%) reported high concern with herbicide-resistant weeds, and crop rotation (>74%) was the most common strategy listed to control and mitigate the development of herbicide-resistant weeds. A chi-square test of homogeneity showed that strategies implemented to control herbicide-resistant weeds and mitigate the evolution of herbicide-resistant weeds were not dependent on occupation type (farmer, consultant, or industry rep) nor on years of involvement in rice production. Respondents failed to control ECG 44% of the time with their first postemergence herbicide. After initial herbicide failure, 53% of respondents stated two additional herbicide applications were required to control ECG escapes while another 21% of respondents stated it was never controlled. The average ECG population at 2020 harvest was between 0.1 and 1.0 plant m−2 according to 44% of the respondents; however, 41% of respondents indicated an ECG density of 2 to 10 plants m−2 at 2020 harvest. The reported annual average cost of herbicides for rice weed control was $266.40 ha−1 with ECG accounting for 81% of the total cost. Average yield loss attributed to ECG was estimated to be 505–959 kg ha−1 (economic loss of $134–254 ha−1). However, yield loss in the most heavily infested fields was estimated to be 757–1,464 kg ha−1 (economic loss of $200–387 ha−1). Effective, non-chemical approaches to weed management were ranked as the least important current research or educational effort, indicating a paradigm shift in rice producers' weed control line of thought is needed with dwindling herbicide options due to herbicide resistance.

Current Status of Herbicide Resistance in the Iberian Peninsula: Future Trends and Challenges

The evolution of herbicide resistance in weeds has emerged as one of the most serious threats to sustainable food production systems, which necessitates the evaluation of herbicides to determine their efficacy. The first herbicide resistance case in the Iberian Peninsula was reported about 50 years ago, wherein Panicum dichotomiflorum was found to be resistant (R) to atrazine in Spanish maize fields. Since then, herbicide resistance has evolved in 33 weed species, representing a total of 77 single-herbicide-resistance cases in this geographic area: 66 in Spain and 11 in Portugal. Changes in agricultural practices, namely the adoption of non-tillage systems and the increased use of herbicides, led to the selection of weed biotypes resistant to a wide range of herbicides. Nowadays the most important crops in Spain and Portugal (maize, winter cereals, rice, citrus, fruits, and olive orchards) are affected, with biotypes resistant to several mechanisms of action (MoAs), namely: ALS inhibitors (20 species), ACCase inhibitors (8 species), PS II inhibitors (18 species), and synthetic auxin herbicides (3 species). More recently, the fast increase in cases of resistance to the EPSPS-inhibiting herbicide glyphosate has been remarkable, with 11 species already having evolved resistance in the last 10 years in the Iberian Peninsula. The diversity of resistance mechanisms, both target-site and non-target-site, are responsible for the resistance to different MoAs, involving point mutations in the target site and enhanced rates of herbicide detoxification, respectively. More serious are the 13 cases reported with multiple-herbicide resistance, with three cases of resistance to three–four MoAs, and one case of resistance to five MoAs. Future research perspectives should further study the relationship between management strategies and the occurrence of TSR and NTSR resistance, to improve their design, develop monitoring and diagnostic tools for herbicide resistance, and deepen the study of NTSR resistance.

A novel Phe‐206‐Leu mutation in acetolactate synthase confers resistance to penoxsulam in barnyardgrass (Echinochloa crus‐galli (L.) P. Beauv)

Barnyardgrass (Echinochloa crus-galli (L.) P. Beauv) has evolved resistance to the acetolactate synthase (ALS) inhibitor penoxsulam which is used to control weeds in rice fields in China. The present study is conducted to identify the target-site resistance (TSR) mechanisms conferring resistance in a penoxsulam-resistant population. The ALS sensitivity in vitro of the resistant population was sixfold lower to penoxsulam than that of the sensitive population. ALS sequencing revealed that no known mutation conferring ALS herbicide resistance was detected. However, a novel mutation Phe-206-Leu was identified in the ALS gene. Additionally, ALS gene expression level of the resistant population was lower than that of the sensitive population. Therefore, the penoxsulam resistance was not due to the overexpression of ALS gene. Molecular docking revealed that this mutation may change the interaction of the penoxsulam-ALS binding and weaken its mutual affinity by approximately 10%. Arabidopsis thaliana transformed with mutant ALS had fourfold greater resistance to penoxsulam and varied cross-resistance to other ALS herbicides than those transformed with sensitive ALS. Mutant and sensitive ALS proteins expressed by the baculovirus system exhibited different in vitro penoxsulam sensitivity levels. Mutant ALS had eightfold lower sensitivity to penoxsulam than sensitive ALS. This report provides clear evidence that the ALS mutation at position 206 (Phe-206-Leu) confers penoxsulam resistance in barnyardgrass. Phe-206 was confirmed to be the ninth amino acid residue related to ALS herbicide resistance in weeds. © 2022 Society of Chemical Industry.

Crystal structure of Arabidopsis thaliana HPPK/DHPS, a bifunctional enzyme and target of the herbicide asulam

Herbicides are vital for modern agriculture, but their utility is threatened by genetic or metabolic resistance in weeds, as well as regulatory barriers. Of the known herbicide modes of action, 7,8-dihydropterin synthase (DHPS), which is involved in folate biosynthesis, is targeted by just one commercial herbicide, asulam. A mimic of the substrate para-aminobenzoic acid, asulam is chemically similar to sulfonamide antibiotics, and although it is still in widespread use, asulam has faced regulatory scrutiny. With an entire mode of action represented by just one commercial agrochemical, we sought to improve the understanding of its plant target. Here we solve a 2.3 Å resolution crystal structure for Arabidopsis thaliana DHPS that is conjoined to 6-hydroxymethyl-7,8-dihydropterin pyrophosphokinase (HPPK), and we reveal a strong structural conservation with bacterial counterparts at the sulfonamide-binding pocket of DHPS. We demonstrate that asulam and the antibiotic sulfamethoxazole have herbicidal as well as antibacterial activity, and we explore the structural basis of their potency by modeling these compounds in mitochondrial HPPK/DHPS. Our findings suggest limited opportunity for the rational design of plant selectivity from asulam and indicate that pharmacokinetic or delivery differences between plants and microbes might be the best ways to safeguard this mode of action.

Emerging weed resistance increases tillage intensity and greenhouse gas emissions in the US corn-soybean cropping system.

Tillage is a common agricultural practice that helps prepare the soil and remove weeds. However, it remains unknown how tillage intensity has evolved and its effect on net greenhouse gas (GHG) emissions. Here, using a process-based modelling approach with a multi-source database, we examined the change in tillage intensity across the US corn-soybean cropping systems during 1998-2016 and the impact of tillage intensity on soil GHG emissions. We found that tillage intensity first decreased and then, after 2008, increased, a trend that is strongly correlated with the adoption of herbicide-tolerant crops and emerging weed resistance. The GHG mitigation benefit (-5.5 ± 4.8 TgCO2e yr-1) of decreasing tillage intensity before 2008 has been more than offset by increased GHG emissions (13.8 ± 5.6 TgCO2e yr-1) due to tillage reintensification under growing pressure of weed resistance. As weed resistance persists or grows, tillage intensity is anticipated to continue rising, probably increasing GHG emissions. Our results imply that farmers' choices in managing herbicide resistance may help mitigate agricultural GHG emissions, underscoring the importance of an alternative strategy to control weeds.

Changes in Dicamba Use are Ahead

The first steps in the development of dicamba tolerant transgenic plants were conducted by Sandoz Crop Protection in Palo Alto, CA and then contractually followed up at the University of Nebraska. The subsequent development by Monsanto of soybean and cotton varieties that would tolerate post-emergent application of dicamba substantially changed the use patterns of dicamba in the United States. Transgenic dicamba-tolerant (DT) seeds were first approved in 2016 in the United States, although the post-emergent use of dicamba was not legal that year. In 2017 and 2018, there was substantial market penetration of DT soybean and cotton seeds into the market and the occurrence of dicamba off-target movement (OTM) was highly variable across the United States. The driving force behind these new seed traits was the widespread failure of glyphosate to control broadleaf weeds effectively, especially those from the Conyza and Amaranthus genera. Herbicide research and development in the United States has historically involved both industry and academic weed scientists usually operating in a symbiotic and mutually respectful relationship, although there may have been disagreements at times about some aspects of herbicides and their development. The relatively recent introduction of DT varieties and legal post-emergent dicamba in the United States was a dynamic time for weed control, and adoption of DT crops and subsequent OTM of dicamba greatly changed the working relationships between academic scientists and representatives from Monsanto and some other private companies. Perhaps the greatest change was the lack of access of research materials that would be available to academic scientists for evaluation prior to the retail sale of those materials. Historically, academic scientists would have the ability to evaluate various new technologies and provide objective, independent comments on their potential utility prior to commercialisation. Monsanto largely restricted access to the DT seeds or new herbicide formulations. There are some states that have long-established policies that they will not recommend a new herbicide technology unless they have examined it under their specific field conditions. For example, University of Arkansas researchers would not recommend the use of post-emergent dicamba on DT crops when it first became legal to use. Monsanto responded by filing legal challenges of various types against the University of Arkansas faculty, including 64 exhibits of various legal aspects. Many other states had varying degrees of restrictions placed upon their research efforts, and most scientists had to sign various forms of confidentiality agreements to obtain access to the research material from Monsanto. There were two major differences in the dicamba labels when first introduced in 2017 and then again two years later. The first major difference was an entire section on herbicide resistance confirmation validation and management that was clearly stated on the label. The authors of this paper remind the readers that the reason we have dicamba being used is because of the wholesale failure of glyphosate resistance management systems. The golden era of weed control, essentially 100% weed control with no crop injury, was lost due to the complete lack of any resistance management strategies. The US EPA added label language hopefully to avoid evolution of resistance in weeds from happening again with essentially any new herbicide. Many herbicide users expect all new labels to include resistance management language. The second obvious change to the label was the duration of validity, which was normally many years in previous pesticide registrations. The first dicamba label, which came out in 2017, was valid for only two years. The next label which came out in 2019, was only valid for five years, although there is widespread speculation on the future of that label.

Effect of different herbicides on Bidens pilosa and Euphorbia heterophylla biotypes resistant to ALS inhibitors

Select herbicides with different mechanism of action is a satisfactory option for resistant weed control. Then, the present work aimed to study the efficiency of different herbicides and their mixtures on Bidens pilosa (blackjack) and Euphorbia heterophylla (wild poinsettia) biotypes, resistant to ALS herbicides in two development stages. The trials we arranged in a completely randomized design with four replications. The treatments tested were (g a.i/a.e ha-1): imazethapyr at 70 and 140 (WG formulation) + 1.0% Assist; imazethapyr at 57.6 and 72 (SL formulation) + 1.0% Assist; imazapic + imazethapyr at 56 and 70 + 1.0% Assist; glyphosate + imazethapyr (596); saflufenacil + glyphosate at 35 + 720 + 0.5% Dash in tank mix, glyphosate at 720 and, a control without herbicide application. Control efficiency was evaluated, as well as dry matter accumulation at the end of the studies. Plants of both species were more susceptible to herbicides at the early stage of development (2 to 4 leaves). The treatments with saflufenacil + glyphosate, (imazethapyr + glyphosate) and glyphosate promoted the best controls, regardless of the species studied and the application stage. The mixture with saflufenacil provided the highest control speed, and the mixture (imazethapyr + glyphosate) was less efficient among three excellent treatments when applied to plants in the 4-6 leaf stage. The treatments (imazethapyr, in both formulations) and (imazethapyr + imazapic) were ineffective in controlling the studied biotypes, regardless of dose and developmental stage studied.

Concurrent evolution of seed dormancy and herbicide resistance in field populations of dominant weed species in Western Australian cropping systems

AbstractHerbicide resistance, documented in many economically damaging weed species, is a major threat to global crop production. The injudicious use of herbicides, often in the absence of diverse weed control strategies, poses an immense selection pressure on weed communities for resistance evolution and weed adaptive traits such as high seed dormancy. This study evaluates the interaction among developing herbicide resistance, seed size, and seed dormancy of ripgut brome (Bromus diandrus Roth), wild oat (Avena fatua L.), and hare barley [Hordeum leporinum Link; syn. Hordeum murinum L. ssp. leporinum (Link) Arcang.] collected from within intensively managed fields (in-crop) in comparison with populations in surrounding ruderal (non-crop disturbed) areas with no history of exposure to herbicides within the Western Australian grainbelt. Seed size of the three species varied by farming system (continuous cereal-intensive annual crops, diverse annual crops, pasture based) and habitat (in-crop, ruderal). Field populations of H. leporinum and B. diandrus tended to have greater seed size compared with ruderal populations. Larger seeds had significantly more dormancy in all three weed species. Field-collected populations that were exposed to herbicide applications for at least the past 5 yr exhibited significantly greater seed dormancy compared with their counterparts present in ruderal areas within the same geographic area. The association between increased seed dormancy and developing multiple herbicide resistance further complicates effective weed management.

Reliable and rapid identification of glyphosate-resistance in the invasive weed Amaranthus palmeri in China.

Glyphosate-resistant invasive plants, including Amaranthus palmeri S. Watson, have greatly challenged management of new invasions. Elucidating their glyphosate resistance levels rapidly and accurately will better inform management strategies. Quantitative real-time PCR (qPCR) has been used to identify glyphosate resistance in A. palmeri by detecting gene copy numbers of 5-enolpyruvylshikimate-3-phosphate synthase (EPSPS), an enzyme inhibited by glyphosate. However, qPCR can only indirectly determine copy numbers because it requires a calibrator sample; it also lacks standardization, thus limiting its usefulness. Droplet digital PCR (ddPCR) is a new method to detect copy number directly and precisely. We evaluated ddPCR as a tool to determine glyphosate-resistance level while using qPCR and glyphosate dose response (GDR) assays as reference technologies to compare performance and efficiency between methods. We identified seven susceptible and seven resistant populations of A. palmeri using the GDR assay. Resistant levels detected by qPCR and ddPCR were generally consistent with the GDR results. Although detected values obtained by qPCR and ddPCR were highly correlated (R2 =0.94), ddPCR results had a lower proportion of non-ideal values (36%) with better accuracy (100%) and specificity (100%) than those of qPCR results. Our findings demonstrate that ddPCR offers improved accuracy and specificity in detecting EPSPS gene copy numbers and is a robust and rapid method for glyphosate-resistance identification in A. palmeri. Our research is the first to measure glyphosate resistance in A. palmeri by ddPCR assay and will shed light on future applications of ddPCR in identifying herbicide resistance in other invasive weeds. © 2022 Society of Chemical Industry.

Transpiration Responses of Herbicide-Resistant and -Susceptible Palmer Amaranth (Amaranthus palmeri (S.) Wats.) to Progressively Drying Soil

Drought events are predicted to increase in the future. Evaluating the response of herbicide-resistant and -susceptible weed ecotypes to progressive drought can provide insights into whether resistance traits affect the fitness of resistant weed populations. Two experiments were conducted in the greenhouse between January and May 2021 to evaluate drought tolerance differences between Palmer amaranth accessions resistant to S-metolachlor or glyphosate and their susceptible counterparts. The accessions used were S-metolachlor-resistant (17TUN-A), a susceptible standard (09CRW-A), and glyphosate-resistant (22–165 EPSPS copies) and glyphosate-susceptible (3–10 EPSPS copies) plants from accession 16CRW-D. Daily transpiration of each plant was measured. The daily transpiration rate was converted to normalized transpiration ratio (NTR) using a double-normalization procedure. The daily soil water content was expressed as a fraction of transpirable soil water (FTSW). The threshold FTSW (FTSWcr), after which NTR decreases linearly, was estimated using a two-segment linear regression analysis. The data showed differences between S-metolachlor-resistant and -susceptible accessions (p ≤ 0.05). The FTSW remaining in the soil at the breakpoint for the S-metolachlor-susceptible accession (09CRW-A) was 0.17 ± 0.007. The FTSW remaining in the soil at the breakpoint for the S-metolachlor-resistant accession (17TUN-A) was 0.23 ± 0.004. The FTSW remaining in the soil at the breakpoint for the glyphosate-resistant and glyphosate-susceptible plants (16CRW-D) was 0.25 ± 0.007 and 0.25 ± 0.008, respectively. Although the mechanism endowing resistance to S-metolachlor might have contributed to increased drought tolerance, follow-up experiments are needed in order to verify this finding. Increased EPSPS copy numbers did not improve the drought tolerance of Palmer amaranth. As droughts are predicted to increase in frequency and severity, these results suggest that S-metolachlor-resistant and glyphosate-resistant Palmer amaranth populations will not be at a competitive disadvantage compared to susceptible genotypes. Alternative and diverse management strategies will be required for effective Palmer amaranth control, regardless of herbicide resistance status.

In vitro and in vivo cytotoxicity assessment of glyphosate and imazethapyr-based herbicides and their association

ABSTRACT Resistance to glyphosate herbicide has initiated usage of combined application of herbicides as a weed control measure. Imazethapyr-based herbicides associated with glyphosate herbicide seem to be an alternative to suppress weed resistance. The aim of this study was to examine the adverse effects of Glyphosate Atanor 48® (ATN) and Imazethapyr Plus Nortox® (IMZT) formulations in both single forms and mixtures using HepG2 cells and zebrafish early-life stages models. Data demonstrated cytotoxicity due to exposure to ATN, IMZT for both models, as follows: (1) ATN (0.5 mg/L), IMZT (5 mg/L), and M3 (0.05 mg/L ATN + 5 mg/L IMZT) increased cytotoxicity by disturbing the mitochondrial activity of HepG2 cells 24 hr after exposure; (2) ATN and IMZT (5 mg/L), and M3 (0.05 mg/L ATN + 5 mg/L IMZT) also decreased the integrity of the membrane of HepG2 cells after 24 hr incubation; (3) only ATN and IMZT (5 mg/L) in their single forms diminished the mitochondrial potential of zebrafish; (4) ATN (single form) at 0.5 mg/L induced apoptosis in zebrafish larvae. In conclusion, these herbicides in their single forms appeared to produce greater cytotoxicity to HepG2 cells and zebrafish compared to the herbicide mixtures.

Dicationic Herbicidal Ionic Liquids Comprising Two Active Ingredients Exhibiting Different Modes of Action.

In the framework of this study, dicationic herbicidal ionic liquids (HILs) containing tetramethylene-1,4-bis(decyldimethylammonium) and dodecylmethylene-1,12-bis(decyldimethylammonium), including two different herbicidal anions exhibiting different modes of action, were synthesized and characterized. One herbicide incorporated into the HILs was a tribenuron-methyl belonging to ALS inhibitors, while the second herbicidal anion was a synthetic auxin that acts as a growth regulator, namely 2,4-dichlorophenoxyacetate (2,4-D), 2-(2,4-dichlorophenoxy)propionate, (2,4-DP), 2,4,5-trichlorophenoxyacetate (2,4,5-T), 4-chloro-2-methylphenoxyacetiate (MCPA), 2-(4-chloro-2-methylphenoxy)propionate (MCPP), and 4-chlorophenoxyacetate (4-CPA). The obtained products were found to be unstable and decomposed, which can be attributed to the presence of an additional methyl group within the sulfonylurea bridge of the tribenuron-methyl. The synthesized HILs exhibited good affinity with polar and semipolar solvents, with ethyl acetate and hexane as the only solvents that did not dissolve the HILs. Greenhouse tests demonstrated that most of the obtained HILs were more effective than the reference herbicide containing tribenuron-methyl. The length of the alkyl chain in the cation also influenced the effectiveness of the HILs. Better effects were observed for dodecylmethylene-1,12-bis(decyldimethylammonium) cations compared to tetramethylene-1,4-bis(decyldimethylammonium). Therefore, the novel dicatonic HILs showed to integrate the advent of the combination of the different herbicides into a single molecule, enhance herbicidal efficacy, and reduce the risk of weed resistance due to the various modes of action of the applied treatment.

Global drivers of herbicide-resistant weed richness in major cereal crops worldwide.

BACKGROUNDThe number of herbicide‐resistant weeds differs across the globe but the reasons for this variation are poorly understood. Taking a macroecological approach, the role of six drivers of herbicide resistance in a country was examined for barley, maize, rice and wheat crops worldwide. Drivers captured agronomic measures (crop harvested area, herbicide and fertilizer input) as well as sources of sampling bias that result in under‐reporting of herbicide resistance (human population density, research intensity and time since the first record of resistance).RESULTSDepending on the crop, best subset regression models explained between 60% and 80% of the variation in herbicide‐resistant weeds recorded in countries worldwide. Global prevalence of herbicide‐resistant weeds is likely underestimated, especially in countries with limited capability in herbicide research. Numbers of resistant weeds worldwide will continue to increase. Agricultural intensification, captured by fertilizer and herbicide input, as well as further expansion of crop harvested area are primary drivers of future herbicide‐resistant weeds.CONCLUSIONBecause the evolution of herbicide resistance lags behind the selection pressures imposed by fertilizer and herbicide inputs, several countries (e.g. Brazil, South Africa, Uruguay) appear to exhibit a ‘herbicide resistance debt’ in which current agronomic conditions have set the scene for higher numbers of herbicide‐resistant weeds than currently observed. Future agricultural expansion will lead to more herbicide‐resistant weeds, especially in developing countries as their economies grow and where herbicide resistance is currently under‐reported. A global strategy for increasing national capability in herbicide resistance research is needed. © 2022 The Author. Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

Drought exposure leads to rapid acquisition and inheritance of herbicide resistance in the weed Alopecurus myosuroides.

Globally, herbicide resistance in weeds poses a threat to food security. Resistance evolves rapidly through the co‐option of a suite of physiological mechanisms that evolved to allow plants to survive environmental stress. Consequently, we hypothesize that stress tolerance and herbicide resistance are functionally linked. We address two questions: (i) does exposure to stress in a parental generation promote the evolution of resistance in the offspring? (ii) Is such evolution mediated through non‐genetic mechanisms? We exposed individuals of a grass weed to drought, and tested whether this resulted in herbicide resistance in the first generation. In terms of both survival and dry mass, we find enhanced resistance to herbicide in the offspring of parents that had been exposed to drought. Our results suggest that exposure of weeds to drought can confer herbicide resistance in subsequent generations, and that the mechanism conferring heritability of herbicide resistance is non‐genetic.

British Crop Production Council (BCPC) Virtual Diseases Review (October 2021): Exploring Alternatives to Enhance Plant Health

This online conference opened with a particular instruction to delegates – arrive with an open mind. No doubt this arose from the common perception that biological alternatives to synthetic pesticides are a less reliable and hence more risky means of crop protection. In her Introduction the Chairperson Kate Storer (ADAS) emphasized the need for, and growing interest in, alternative approaches to plant health, given the current challenges facing agriculture. While definitions of plant health vary there is a consensus that the genetic potential of crops cannot be realized by a single means, and a more holistic concept is required if we are to achieve sustainable production systems with a lower carbon footprint. The yield of some crops such as wheat have plateaued in recent years, and there is evidence for higher annual variability in yield, in spite of the usual inputs of fertilizers and fungicides. This may be a result of a more volatile climate, as well as the erosion of efficacy of some crop protection chemicals due to the development of resistance in target pests, weeds and pathogens. Increasing the resilience of crops is now a high priority. There is a renewed focus on the plant-microbial interactions influencing crop performance, from the well-known mutualistic associations such as mycorrhizas, to the complex communities of microbes colonizing plant surfaces and tissues (the microbiome). These have a range of potential effects on plant health, including improved nutrition, inhibition of pathogens, and priming plant defence. Optimizing these associations is one aim of current research, and they may also be a potentially rich source of biologically active metabolites. Understanding the impact of management practices, such as ploughing and crop rotations, on beneficial interactions is also important to maximize their benefits.