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Summary: Populations of Polypogon fugax have developed resistance to many acetyl‐CoA carboxylase (ACCase)‐inhibiting herbicides. This resistance threats the effectiveness and sustainability of herbicide use. In our previous research, a field P. fugax population exhibited GST‐based metabolic resistance to the widely used ACCase‐inhibiting herbicide quizalofop‐p‐ethyl. Here, in this current study, we identified and characterized two GST genes (named as PfGSTF2 and PfGSTF58) that showed higher expression levels in the resistant than the susceptible population. Transgenic rice calli overexpressing PfGSTF2, but not PfGSTF58, became resistant to quizalofop‐p‐ethyl and haloxyfop‐R‐methyl. This reflects similar cross‐resistance pattern to what was observed in the resistant P. fugax population. Transgenic rice seedlings overexpressing PfGSTF2 also exhibited resistance to quizalofop‐p‐ethyl. In contrast, CRISPR/Cas9 knockout of the orthologue gene in rice seedlings increased their sensitivity to quizalofop‐p‐ethyl. LC–MS analysis of in vitro herbicide metabolism by Escherichia coli‐expressed recombinant PfGSTF2 revealed that quizalofop (but not haloxyfop) was detoxified at the ether bond, generating the GSH‐quizalofop conjugate and a propanoic acid derivative with greatly reduced herbicidal activity. Equally, these two metabolites accumulated at higher levels in the resistant population than the susceptible population. In addition, both recombinant PfGSTF2 and PfGSTF58 can attenuate cytotoxicity by reactive oxygen species (ROS), suggesting a role in plant defence against ROS generated by herbicides. Furthermore, the GST inhibitor (NBD‐Cl) reversed resistance in the resistant population, and PfGSTF2 (but not PfGSTF58) responded to NBD‐Cl inhibition. All these suggest that PfGSTF2 plays a significant role in the evolution of quizalofop resistance through enhanced herbicide metabolism in P. fugax. [ABSTRACT FROM AUTHOR]

To evaluate the efficacy of several herbicides for weed control in wheat fields, an experiment carried out as complete randomized block design with three replications at Lorestan province during 2020-2021. The experiment treatment was the pure clodinafop-propargyl (Topik®) application at 32, 48, 64 and 80 g active ingredients (a.i.) ha-1, pinoxaden pure application of pinoxaden (Axial®) ans also ready mix of pinoxaden + clodinafop-propargyl (binary mixture) (Traxos®) application at 33.75, 50.62, 67.5 and 84.37 g a.i. ha-1. The results showed that herbicide different doses were significant on all weeds density and dry weight. All crop characteristics such as biological yield, spike length, grain yield except crop height were significant by herbicide different doses as well. But seed 1000 weight was not significant by herbicide herbicide different doses. Also based on results, some weeds such as wild oat, ryegrass, blackgrass and canarygrass were sensitive to clodinafop-propargyl and pinoxaden pure application as their reduced dry weight compared to control were 24.01, 29.31, 27.71 and 51.92 for clodinafop-propargyl and 30.84, 22.32, 20.90 and 51.29 for pinoxaden, respectively. Binary mixture of pinoxaden + clodinafop-propargyl had more efficacy than their pure application. According to visual observations results, the only 50 percent control of wild barley, rye and downy brome were achieved when the mixture of pinoxaden + clodinafop-propargyl were used at high dose. The highest of grain yield was also attained at doses of 67.5 and 84.37 g a.i. ha-1 of pinoxaden + clodinafop-propargyl which increased grain yield 18.32 increase compared to the pure application of each herbicide. Therefore, due to the frequent application of clodinafop-propargyl and pinoxaden and the possibility occurring of weed resistance to these herbicides, using mixture of pinoxaden + clodinafop-propargyl can be suitable not only to more effective in weeds control but also as a appropriate replacement in herbicide rotation for managing and delaying of possible resistance in weeds.

Weed management is a critical factor influencing wheat yield and quality. Post-emergence herbicides offer a flexible approach to controlling weeds after crop emergence. The paper critically evaluates the performance of different herbicide classes and their impact on wheat productivity, weed resistance, weed spectrum, crop safety, and herbicide resistance control. This field experiment was conducted in Randomized Block Design with ten treatments and three replications in which six different herbicides and their combination are used with a control (150:60:40 NPK/ha). Among herbicide treatments significantly highest plant height (67.72 cm) dry weight (16.48 g), number of tillers (107.33) and lowest weed dry weight of Phalaris minor (7.8 g/m²) Rumex dentatus (0 g/m²) total other weeds (0 g/m²) and total weeds (8.8 g/m²) while Rumex dentatus and total other weeds are completely controlled in EPoE and PoE application of aclonifen + diflufenican. [ABSTRACT FROM AUTHOR]

This paper assesses the environmental impacts associated with changes in pesticide use with GM crops at a global level. The main technologies impacting on pesticide use have been crops modified to be tolerant to specific herbicides so as to facilitate improved weed control and crops resistant to a range of crop insect pests that otherwise damage crops or typically require the application of insecticides to control them. Over the 24 year period examined to 2020, the widespread use of GM insect resistant and herbicide tolerant seed technology has reduced pesticide application by 748.6 million kg (−7.2%) of active ingredient and, as a result, decreased the environmental impact associated with insecticide and herbicide use on these crops (as measured by the indicator, the Environmental Impact Quotient (EIQ)) by a larger 17.3% between 1996 and 2020. The technology that has delivered the largest change in pesticide use has been insect resistant cotton, where a 339 million kg of active ingredient saving has occurred and the associated environmental impact (as measured by the EIQ indicator) has fallen by about a third.

The conversion of tallgrass prairie to agriculture has negatively affected provisioning of ecosystem services. Successful restoration of ecosystem services could depend on management decisions applied during revegetation projects. We examined the effects of three management decisions (seed mix design, planting time, and first‐year mowing) on targeted ecosystem services (erosion control, weed resistance, and pollinator resources). We tested three seed mixes of varying diversity and grass‐to‐forb seeding ratios: Economy mix (21 species, 3:1 grass:forb), Pollinator mix (38 species, 1:3), and Diversity mix (71 species, 1:1). We established plots at two planting times (dormant‐season and spring) with or without first‐year mowing. To assess ecosystem services, we measured stem density, canopy cover, and floral density and richness of sown species in the second year after planting. The Economy mix had the highest stem density and cover but lowest floral density and richness. The Pollinator mix had the lowest stem density and cover but highest floral density. The Diversity mix had comparable stem density and cover to the Economy mix and comparable floral density and richness to the Pollinator mix. Mowing accelerated native plant establishment in all seed mixes. Dormant‐season planting improved establishment of spring and fall forbs and favored cool‐season graminoids over warm‐season grasses. All three management decisions influenced ecosystem outcomes, and comparison to a previous study revealed these effects to be robust to variation in site and climatic conditions. We recommend a diverse, balanced seed mix design, first‐year mowing, and dormant‐season planting to improve multifunctionality of conservation projects. [ABSTRACT FROM AUTHOR]

Digitaria ciliaris var. chrysoblephara is one of the most competitive and problematic grass weeds in China. Metamifop is an aryloxyphenoxypropionate (APP) herbicide that inhibits the activity of acetyl-CoA carboxylase (ACCase) of sensitive weeds. Following the introduction of metamifop to China in 2010, it has been continuously used in rice paddy fields, thereby substantially increasing selective pressure for resistant D. ciliaris var. chrysoblephara variants. Here, populations of D. ciliaris var. chrysoblephara (JYX-8, JTX-98, and JTX-99) were observed to be highly resistant to metamifop, with resistance index (RI) values of 30.64, 14.38, and 23.19, respectively. Comparison of resistant and sensitive population ACCase gene sequences revealed that a single nucleotide substitution from TGG to TGC resulted in an amino acid substitution from tryptophan to cysteine at position 2,027 in the JYX-8 population. No corresponding substitution was observed for JTX-98 and JTX-99 populations. The ACCase cDNA of D. ciliaris var. chrysoblephara was successfully obtained by PCR and RACE methods, representing the first amplification of full length ACCase cDNA from Digitaria spp. Investigation of the relative expressions of ACCase gene revealed the lack of significant differences between sensitive and resistant populations before and after herbicide treatments. ACCase activities in resistant populations were less inhibited than in sensitive populations and recovered to the same or even higher levels compared to untreated plants. Whole-plant bioassays were also conducted to assess resistance to other ACCase inhibitors, acetolactate synthase (ALS) inhibitors, auxin mimic herbicide, and protoporphyrinogen oxidase (PPO) inhibitor. Cross-resistance and some multi-resistance were observed in the metamifop-resistant populations. This study is the first to focus on the herbicide resistance of D. ciliaris var. chrysoblephara. These results provide evidence for a target-site resistance mechanism in metamifop-resistant D. ciliaris var. chrysoblephara, while providing a better understanding of cross- and multi-resistance characteristics of resistant populations that will help in the management of herbicide-resistant D. ciliaris var. chrysoblephara. [ABSTRACT FROM AUTHOR]

Herbicide resistance is a significant and increasing problem for growers and land managers in inputintensive agricultural systems worldwide. In Australia and North America, herbicides are the main tools for managing problematic agricultural weeds, with recommended non-herbicidal practices used when convenient and deemed effective. However, farmers usually fail to appreciate the synergies in weed control that can be achieved by stacking effective non-herbicidal tactics within the framework of a farming ‘system’. All of us can learn something from herbicide resistance experiences (good or bad) in other parts of the world; the question is how relevant, practical and useful will the different tactics or strategies be when applied or adapted to my particular agroclimatic region and farming system? The answers may only become known after local research and demonstration studies.

Das Vorkommen resistenter Ungräser stellt für Landwirte und Beratung ein zusätzliches Problem für die langfristige Planung des Unkrautmanagements dar. Wir stellen hier einen Ansatz zur individuellen Risikoermittlung der Resistenzentwicklung und der Ableitung individueller Maßnahmen zur Resistenzvermeidung und Kontrolle von Ungräsern vor. Die Basis für die Entwicklung eines Beratungs- Algorithmus bildet dabei ein deutschlandweit durchgeführtes Monitoring der Jahre 2019-2021. Auf Basis dieser Daten, zusammen mit weiteren externen Daten, wird mit Hilfe von Verfahren des maschinellen Lernens ein Algorithmus erarbeitet, der frühzeitig auf Resistenz-Probleme einzelner Flächen hinweist und eine Anpassung von Maßnahmen vorschlägt. Ein Prototyp ist für die Saison 2022/23 geplant.

Der Befall und die Resistenzsituation von Alopecurus myosuroides Huds., Apera spica-venti (L.) P. Beauv., Bromus spp. und Lolium spp. wurden in den Jahren 2019-2021 untersucht. Es zeigt sich, dass gerade im Jahr 2021 der Befall höher war als in den Jahren davor. Resistenzen wurden gerade bei A. myosuroides und Lolium spp. sowohl bei den ACCase- als auch bei den ALS-Inhibitoren gefunden, während für Bromus spp. und A. spica-venti eher Probleme bei Sulfonylharnstoffen gefunden wurden. Zunehmend beobachten wir jedoch Fälle von Mischverungrasungen mehrerer resistenter Gräser, die die Landwirte zunehmend vor Probleme stellen.

A putative resistant johnsongrass (Sorghum halepense L.) population from a cotton field in northern Greece was studied to determine the levels of resistance to acetyl‐CoA carboxylase (ACCase)‐inhibiting herbicides and elucidate related mechanisms of resistance. The johnsongrass population showed cross‐resistance to the ACCase‐inhibiting herbicides fluazifop‐p‐butyl, quizalofop‐p‐ethyl, and propaquizafop, with poor levels of control even with four times of the recommended rates of these herbicides. However, the johnsongrass population was highly sensitive (100% control) to the ACCase inhibitors cycloxydim and clethodim and to the acetolactate synthase inhibitor nicosulfuron. Amplification and sequencing of the ACCase gene fragment from johnsongrass plants revealed an Ile to Asn substitution at codon 2041 of the ACCase enzyme. This is the first record of a molecularly confirmed ACCase‐resistant johnsongrass population from cotton fields in Europe. These findings highlight a threat against the sustainable use of ACCase‐inhibiting herbicides in controlling johnsongrass and other grasses in cotton fields. [ABSTRACT FROM AUTHOR]

Scholars with an interest in agricultural social change have a long history of studying farmer decision-making. While much of the early research was focused on identifying the individual characteristics of progressive farmers, research has evolved into examinations of the many factors that may influence different types of farm decision-making, including the use of so-called Best Management Practices. We utilize an approach for analyzing farmer decision-making that includes some possible internal and external factors for understanding how farmers are responding to the emerging crisis of herbicide-resistant weeds. Based on survey data collected onfarm managers, we contrast farmers that are using an herbicide-centric approach with those who are adopting practices associated with integrated weed management. Our findings indicate that farm decision-making is a complex process that is influenced by a variety of factors. [ABSTRACT FROM AUTHOR]

In modern agriculture, on large-scale farms using monoculture, reduced tillage and intense chemical protection, the phenomenon of herbicide resistance in weeds is the cause of ecological and economic losses. More and more attempts are made to answer the question about the profitability of reducing agrotechnical treatments and intensifying chemical methods of weed control with a simultaneous intensification of the problem of herbicide resistance in weeds occurring in winter wheat crops, which dominates the structure of cereal sowing in Poland. The main objective of the study was to evaluate the costs of weed control for winter wheat cultivation on large-scale farms where there was no problem of weed resistance and on farms where resistant biotypes were identified. The research was based on a survey conducted among owners of farms cultivating winter wheat in 2019. The collected data were elaborated using basic methods of descriptive statistics and economic analysis. Based on the research results, it was found that with an increase in the area of farms, reduced tillage and monoculture are used more frequently than conventional tillage and crop rotation. At the same time, the commonly used chemical weed control methods are more frequently applied than mechanical ones. Economic efficiency indicators for winter wheat protection against weeds indicate a decrease in this efficiency with an increase in farm size. This is because the larger the farms, the more frequently the occurrence of resistant weed biotypes, which was confirmed by laboratory tests, and farmers more often assumed that such a problem occurred on their farms

The sustainable control of weed populations, particularly resistant species, is a significant challenge in agriculture around the world. The α-aryl-keto-enol (aryl-KTE) class of acetyl-CoA carboxylase (ACCase)-inhibiting herbicides represent a possible solution for the control of resistant grasses even though achieving crop selectivity remains a challenge. Herein, we present some of our investigations into identifying the most promising structural features within the aryl-KTE class that give the highest chance of achieving soybean crop selectivity, whilst also maintaining strong and broad efficacy against problematic weed species. We further examined our results by preparing new aryl-KTE molecules which were evaluated in glasshouse screening assays for their herbicidal efficacy as well as their soybean selectivity. We consider that uniting this approach with other optimization criteria, such as toxicological and environmental safety profiles, will enable the streamlining of crop protection optimizations programmes, ultimately delivering safer and more sustainable solutions to farmers and consumers. © 2024 The Author(s). Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry., (© 2024 The Author(s). Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.)

The ubiquity of chemicals demands new ways of thinking about human–nature assemblages. This article develops a dialogue between agrarian political economy, critical commodity chains research, and chemical geographies through a case study of the world's most widely used agrochemical: glyphosate, commonly known as Monsanto's Roundup. In the 1980s, glyphosate triumphed as a benign biocide that promised both safety and effectiveness. This construct made possible a capitalist agricultural assemblage characterized by chemical pervasiveness, first as a chemical replacement for mechanical tillage and since the 1990s as the chemical input for genetically modified seed packages. The ubiquity that characterizes the glyphosate assemblage is also a geography of uneven development comprising shifting firm networks, policies, and trade. Central to this assemblage since 2000, yet largely ignored, is the outsized expansion of second- and third-tier generic pesticide producers, especially in China, for whom glyphosate is part of a network entry and upgrading development strategy. Today, the glyphosate assemblage faces unprecedented challenges from weed resistance and health controversies. Whether and how the herbicide assemblage restabilizes will be determined by the complex environmental and developmental challenges of chemical agriculture and pervasive chemicals broadly, which highlights the need for a transdisciplinary dialogue that cuts across these domains. [ABSTRACT FROM AUTHOR]

This paper assesses how the use of genetically modified seed (GM) crop seed technology has impacted on greenhouse gas emissions at a global level. The main technologies of relevance are crops modified to be tolerant to specific herbicides so as to facilitate improved weed control and crops resistant to a range of crop insect pests that otherwise damage crops or typically require the application of insecticides to control them. Over the 24 year period examined to 2020, the widespread use of GM insect resistant and herbicide tolerant seed technology has led to important cuts in on-farm fuel use and facilitated farmers moving from plow-based systems to reduced and no tillage systems that they have continued to operate for a number of years. This has led to a significant reduction in the release of greenhouse gas emissions from the GM cropping area, which in 2020 was equal to a saving of 23,631 million kg of carbon dioxide, equivalent to taking 15.6 million cars off the road for a year (equal to 49% of registered cars in the UK). [ABSTRACT FROM AUTHOR]

This paper assesses the environmental impacts associated with changes in pesticide use with GM crops at a global level. The main technologies impacting on pesticide use have been crops modified to be tolerant to specific herbicides so as to facilitate improved weed control and crops resistant to a range of crop insect pests that otherwise damage crops or typically require the application of insecticides to control them. Over the 24 year period examined to 2020, the widespread use of GM insect resistant and herbicide tolerant seed technology has reduced pesticide application by 748.6 million kg (−7.2%) of active ingredient and, as a result, decreased the environmental impact associated with insecticide and herbicide use on these crops (as measured by the indicator, the Environmental Impact Quotient (EIQ)) by a larger 17.3% between 1996 and 2020. The technology that has delivered the largest change in pesticide use has been insect resistant cotton, where a 339 million kg of active ingredient saving has occurred and the associated environmental impact (as measured by the EIQ indicator) has fallen by about a third. [ABSTRACT FROM AUTHOR]

Penoxsulam is a new acetolactate synthase inhibitor (ALS) herbicide developed by Dow AgroSciences. In order to explore the sensitivity of Echinochloa spp. to penoxsulam on rice field, whole-plant bioassay experiments were conducted to evaluate the resistance level of 70 field populations of Echinochloa spp. from main rice production in seven provinces of China. The results showed that 50.0% of the 70 populations had evolved high resistance, 47.1% of the populations was moderate resistance, and only 2.9% of the populations exhibited low resistance. None populations were sensitive to penoxsulam. More than 60% of the populations had evolved high resistance from Hubei, Anhui, Ningxia and Heilongjiang Province. The populations of high level resistance was more than 25% in other three province. More than 60% of the population with moderate level resistance were from Hunan, Jiangxi and Jiangsu Province, and the populations of 20.0%-40.0% were also with moderate level resistance in others 4 provinces. The 10.0% and 12.5% of population were with low level resistance in Hubei and Heilongjiang Province, while other 5 provinces had no low level resistant populations. This work investigated the evaluation and monitoring of the field resistance of populations of Echinochloa spp. to penoxsulam, which provided a theoretical basis for the scientific application of penoxsulam to control Echinochloa spp. in the main rice cultivation area. [ABSTRACT FROM AUTHOR]

Die Ergebnisse aus einem bundesweit durchgeführten Gräser-Resistenzmonitoring werden vorgestellt. Für eine repräsentative Erhebung wurde auf 1121 Feldern im Bundesgebiet die Befallshöhe verschiedener Ungräsern zum Zeitpunkt der Samenreife festgestellt sowie eine Samen-Stichprobe gesammelt. Erfasst wurden dabei Acker-Fuchsschwanz, Gemeiner Windhalm, Trespe-Arten und Welsches Weidelgras. Der Status der Sensitivität gegen zwei H der HRAC-Gruppe A (Axial 50) und B (Atlantis WG) wurde im Biotest (Gewächshaus) erfasst. Die Ergebnisse verdeutlichen, dass der Gräserbefall nach dem Herbizideinsatz im Feld in den meisten Fällen gering ist und somit noch eine gute Kontrolle mit den vom Landwirt eingesetzten Herbiziden besteht. Es zeigt sich jedoch, dass auch bei geringem Befall im Feld Resistenzen nachzuweisen sind, was auf eine starke Selektion durch das eingesetzte Produkt schließen lässt. Resistenzen gegenüber Axial 50 wurden dabei häufiger beobachtet als gegen Atlantis WG.

Black-grass (Alopecurus myosuroides Huds.) and rye-grass (Lolium spp) are very competitive grass weeds. During the last decades, they have evolved resistance to post-emergence herbicides, in particular ACCase- and ALS- inhibitors. This requires more complex weed management strategies. To ensure good control of both weeds, pre-emergence treatments become increasingly important. Particularly flufenacet has become a key herbicide for the control of multiple-resistant black-grass and rye-grass. Yet, in some of those populations, reduced flufenacet efficacy start to be observed. In a screening with black-grass and rye-grass populations of worldwide origins, most populations could be controlled with the registered field rate of flufenacet, however differences in the level of flufenacet efficacy were observed and were in correlation with enhanced flufenacet metabolism. This was particularly the case for rye-grass populations. The use of flufenacet in mixtures with diflufenican, particularly in combination with flurtamone or metribuzin or aclonifen, improved the efficacy significantly. In decreased flufenacet sensitive populations, the efficacy of other pre-emergence herbicides like pendimethalin, prosulfocarb, S-metolachlor, dimethenamid-P and pethoxamid, was also significantly decreased whereas other herbicides like pyroxasulfone or diflufenican remained highly active. This decreased efficacy of flufenacet as well as S-metolachlor was associated with higher metabolism involving glutathione-s-transferases. Although differences between populations were sometimes relatively small, best weed management practices (e.g. application of full dose rates and mixtures) should be applied to reduce selection pressure and prevent the development of resistance. This is particularly important as flufenacet is one of the few still active herbicides suitable for the control of multiple-resistant grass weeds. Use of mixtures associated with agronomic solutions in an Integrated Weed Management approach has to be the main approach.

The main purpose of the article is to assess the economic efficiency of wheat protection in conditions of the occurrence of weed resistance to herbicides in a selected large-scale farm (case study). In modern agriculture, especially in large-scale farms using monoculture, zero tillage and intensive chemical protection, the emerging phenomenon of weed resistance to herbicides is a cause of ecological and economic losses. In Poland, as well as the world, the problem of weed resistance is mainly noted in the case of wheat cultivation, which is ranked first in terms of sown area. Therefore, more and more often attempts are being made to answer the question, what is the profitability of performed weed control operations with the simultaneous occurrence of herbicide resistance. Empirical research was conducted on the basis of data recorded in the book of profits and losses recorded by the farm owner in 2014-2018. The collected data was developed using economic analysis and statistical methods. It was found that, in the examined period, due to the growing problem of the presence of resistant weeds, the use of products to control them increased and the costs of protecting wheat cultivation also increased. The low effectiveness of chemical weed control treatments resulted in a change in the structure of crops in the researched farm in the last year of the study.

Weed control in the U.S. Midwest has become increasingly herbicide-centric due to the adoption of herbicide-tolerant (HT) crops in the 1990s. That integrated weed management (IWM) practices, including ecological and mechanical controls, are scarcely used is concerning. IWM would be a more sustainable form of farming for two reasons. First, it would reduce the negative health and environmental externalities associated with herbicide use. Second, it would reduce the selection pressure on weed populations and the development of weed resistance to some herbicides, thereby reducing the uncertainty of the long-term effectiveness of herbicidal weed control. In this context, we develop an economic framework to clarify the interplay among the different market failures that either contribute to the herbicidal ‘lock-in’ or make it problematic. We then analyse the evidence for and perceptions of these market failures based on twenty-four semi-structured interviews with farmers and experts conducted in 2017, as well as on discussions in the academic literature. To this end, we put into perspective the possible self-reinforcing effects in the adoption path of HT crops, such as increasing farm size, changes in farm equipment, increasing incentives for simplified crop rotations, and the loss of practical knowledge of IWM practices.

BACKGROUND Weedy sunflower (Helianthus annuus L.) is a troublesome weed in row‐crop production fields in South Texas. Populations with suspected resistance to glyphosate were evaluated with 1X and 4X rates (X = 868 g ae ha−1) of the herbicide, followed by a dose–response assay of the most resistant population. Molecular studies were conducted to determine if target‐site mechanisms were responsible for resistance in these populations. Additionally, field experiments were conducted at two locations (Somerville and Granger, TX) to evaluate the effectiveness of different tank‐mix combinations in controlling naturally infesting glyphosate‐resistant (GR) weedy sunflower populations in GR corn. RESULTS: In a study conducted in the growth chamber, seven of the 11 tested populations survived up to the 4X rate of glyphosate. The most‐resistant population (TX15‐11) was 29‐fold more resistant to glyphosate, compared to the susceptible standard. In resistant populations, 5–21 more copies of the EPSPS gene were observed compared to the susceptible standard. In the field studies, tank‐mix applications of glyphosate + halosulfuron‐methyl, glyphosate + prosulfuron, glyphosate + a premix of halosulfuron‐methyl and dicamba or glyphosate + a premix of diflufenzopyr and dicamba effectively controlled GR weedy sunflower populations. CONCLUSION: Glyphosate‐resistance was observed in 81% of the putative resistant weedy sunflower populations tested in this study. Resistance in these populations was conferred primarily by amplification of the EPSPS gene. Effective control of GR weedy sunflower can be achieved by tank‐mixes tested in the current study, which provides acceptable levels of crop safety. © 2020 Society of Chemical Industry [ABSTRACT FROM AUTHOR]

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BACKGROUND Two waterhemp (Amaranthus tuberculatus) populations from Illinois demonstrating multiple‐resistance to acetolactate synthase (ALS)‐, 4‐hydroxyphenylpyruvate dioxygenase, and photosystem II (PSII)‐inhibiting herbicides (designated CHR and SIR) also displayed reduced sensitivity to very‐long‐chain fatty acid‐inhibiting herbicides, including S‐metolachlor. We hypothesized that a physiological mechanism, such as enhanced metabolism, could be responsible for the reduced efficacy of S‐metolachlor. RESULTS : Metabolism experiments indicated that resistant populations degraded S‐metolachlor more rapidly than sensitive populations and equally as rapidly as corn 2–24 h after treatment (HAT). Resistant waterhemp and corn metabolized 90% (DT90) of absorbed S‐metolachlor in less than 3.2 h whereas DT90 values for sensitive waterhemp exceeded 6 h. The glutathione S‐transferase inhibitor 4‐chloro‐7‐nitrobenzofurazon and cytochrome P450‐inhibitor malathion decreased the amount of S‐metolachlor metabolized in resistant waterhemp at 4 HAT but not in sensitive waterhemp or corn, and altered the abundance of certain metabolites in resistant waterhemp. CONCLUSION : Results from this research demonstrate that resistance to S‐metolachlor in these waterhemp populations is due to enhanced herbicide metabolism relative to sensitive populations. In addition, our results indicate that resistant waterhemp might utilize metabolic pathway(s) more intricate than either sensitive waterhemp or corn based on their metabolite profiles. © 2020 Society of Chemical Industry [ABSTRACT FROM AUTHOR]

Agricultural intensification continues to diminish many ecosystem services in the North American Corn Belt. Conservation programs may be able to combat these losses more efficiently by developing initiatives that attempt to balance multiple ecological benefits. In this study, we examine how seed mix design and first year management influence three ecosystem services commonly provided by tallgrass prairie reconstructions (erosion control, weed resistance, and pollinator resources). We established research plots with three seed mixes, with and without first year mowing. The grass‐dominated "Economy" mix had 21 species and a 3:1 grass‐to‐forb seeding ratio. The forb‐dominated "Pollinator" mix had 38 species and a 1:3 grass‐to‐forb seeding ratio. The grass:forb balanced "Diversity" mix, which was designed to resemble regional prairie remnants, had 71 species and a 1:1 grass‐to‐forb ratio. To assess ecosystem services, we measured native stem density, cover, inflorescence production, and floral richness from 2015 to 2018. The Economy mix had high native cover and stem density, but produced few inflorescences and had low floral richness. The Pollinator mix had high inflorescence production and floral richness, but also had high bare ground and weed cover. The Diversity mix had high inflorescence production and floral richness (comparable to the Pollinator mix) and high native cover and stem density (comparable to the Economy mix). First year mowing accelerated native plant establishment and inflorescence production, enhancing the provisioning of ecosystem services during the early stages of a reconstruction. Our results indicate that prairie reconstructions with thoughtfully designed seed mixes can effectively address multiple conservation challenges. [ABSTRACT FROM AUTHOR]

Aims: The mechanisms of weed resistance to herbicides are generally thought to include alteration of the target site, enhanced detoxification, and sequestration. Endophytes can promote plant growth and enhance tolerance to abiotic stress. To date, how endophytes affect weed resistance to herbicides has not been reported. Methods: The dose-response tests performed on the derived seed batches in our study were used to test the toxicity of Polypogon fugax to quizalofop-p-ethyl. The endophytes were isolated, and the degradation rate of endophytes to quizalofop-p-ethyl was measured. The endophyte was inoculated onto the susceptible P. fugax using inoculation techniques. The effect of germicide on the toxicity of quizalofop-p-ethyl to the resistant P. fugax plants was observed. Results: Resistance was confirmed in several tested P. fugax populations. Among them, the population collected from Qingshen County, Sichuan Province (QCSP) had the highest resistance index. The number and degradation rate of quizalofop-p-ethyl degrading endophytes was lower in the susceptible population than in the QCSP resistant population. The isolated KT4 strain from the QCSP population had the highest degradation rate. The 16S rDNA sequence of KT4 was identical to that of Sphingomonas sp. The treatments that contain inoculating endophytes KT4 enhanced the resistance to quizalofop-p-ethyl in the susceptible population. Treatments containing a combination of quizalofop-p-ethyl with either kasugamycin or jinggangmycin, which can kill or inhibit endophytes growth, reduced the resistance level of the QCSP population to quizalofop-p-ethyl. Conclusions: This is the first report that endophytes can degrade quizalofop-p-ethyl to enhance resistance in P. fugax. [ABSTRACT FROM AUTHOR]

The excessive use of glyphosate by Brazilian citrus growers leads to a vicious and unsustainable circle: Increasing the glyphosate use and the selection pressure of resistant/tolerant weeds, as well as the phytointoxication of the crop. In addition, there is speculation on the consequences of using glyphosate and the studies are not conclusive. Therefore, this study aimed to evaluate the glyphosate management in citrus orchards by assessing its effects in a 5-year field experiment using different doses and application frequencies. Here, we determine the weed control levels, the orchard growth and fruit yield, as well as the economic viability of the treatments. Higher weed control was observed more often with the increasing frequency of glyphosate application, and occasionally with increasing doses. However, some species predominated even at high glyphosate usage, such as BIDPI (Bidens pilosa (L.)), RAPRA (Raphanus raphanistrum (L.)), and ERICA (Conyza canadensis (L.) Cronquist). Phytotoxicity symptoms were demonstrated up to the fourth year of the orchard, and onwards the plants no longer expressed them. This was a highlight, since there was a decrease over time in growth (up to 5.3 m3) and fruit yield (up to 36.3 t ha−1), with losses that reached −56% of the total income. This is the first report to demonstrate that the increase in glyphosate usage can occasionally increase weed control, but it can also decrease orchard development and its financial viability.

Saflufenacil has been used to control glyphosate resistant weeds, including hairy fleabane. There are several glyphosate formulations, which are related to different salts and adjuvants. Differences between these formulations may result in variations in efficacy, especially in the face of unfavorable environmental conditions, such as the occurrence of unexpected rainfall after application. The objective of this study was to evaluate the control of hairy fleabane with saflufenacil in tank mix with different formulations of glyphosate subjected to simulated rainfall after application. The treatments evaluated were salts of glyphosate (isopropylamine, potassium and ammonium salt), different periods of simulated rainfall after herbicide application (30, 120 and 240 min, and no rainfall), and the presence or absence of saflufenacil and a non-ionic adjuvant. Absorption of saflufenacil by hairy fleabane is rapid, since simulated rainfall after 30 min after application did not result in loss of efficiency when the herbicide is applied with adjuvant. The association of isopropylamine and ammonium salts of glyphosate with saflufenacil increases the control of hairy fleabane and prevents the occurrence of regrowth when rainfall occurs at 30 min after the application. The occurrence of simulated rainfall after 240 min reduces the glyphosate efficiency by 30%, 15% and 60% for the isopropylamine, potassium and ammonium salt formulations, respectively. The addition of adjuvant improves the efficiency of glyphosate salt of potassium by 40%. The response of the mixture of glyphosate and saflufenacil is variable, mainly in situations of rainfall after application. [ABSTRACT FROM AUTHOR]

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BACKGROUND Herbicides inhibiting the synthesis of very long‐chain fatty acids (HRAC group K3, WSSA group 15), such as flufenacet, play an important role in weed management strategies, particularly when herbicide resistance to inhibitors with other modes of action, such as acetolactate synthase or acetyl coenzyme A carboxylase (ACCase), has already evolved. So far, only a few cases of resistance towards inhibitors of the synthesis of very long‐chain fatty acids have been described. In this study, we characterized the level of flufenacet resistance in several Lolium spp. field populations and investigated the resistance mechanism. RESULTS: The screening for flufenacet resistance revealed the ability of Lolium spp. populations from several continents to survive flufenacet treatments at and above the field rate. This study demonstrates the way in which flufenacet is detoxified in resistant weed populations. Glutathione was found to be conjugated to flufenacet in Lolium spp. seedlings, and there was evidence that glutathione transferase activity was enhanced in protein extracts from flufenacet‐resistant seedlings. A significant correlation was found between the resistance factor obtained by biotests and the degradation half‐time of flufenacet in ryegrass plants obtained by high‐performance liquid chromatography (HPLC). CONCLUSION: At present, flufenacet resistance is not widespread; however, in certain Lolium spp. populations resistance levels could reach agronomic relevance due to detoxification by glutathione transferases. In Europe especially, only a few herbicide modes of action are registered for the control of Lolium spp. and therefore it is becoming increasingly important to apply best management practices to prevent the spread of flufenacet resistance. © 2019 Society of Chemical Industry [ABSTRACT FROM AUTHOR]

Weed control in the U.S. Midwest has become increasingly herbicide-centric due to the adoption of herbicide-tolerant (HT) crops in the 1990s. That integrated weed management (IWM) practices, including ecological and mechanical controls, are scarcely used is concerning. IWM would be a more sustainable form of farming for two reasons. First, it would reduce the negative health and environmental externalities associated with herbicide use. Second, it would reduce the selection pressure on weed populations and the development of weed resistance to some herbicides, thereby reducing the uncertainty of the long-term effectiveness of herbicidal weed control. In this context, we develop an economic framework to clarify the interplay among the different market failures that either contribute to the herbicidal 'lock-in' or make it problematic. We then analyse the evidence for and perceptions of these market failures based on twenty-four semi-structured interviews with farmers and experts conducted in 2017, as well as on discussions in the academic literature. To this end, we put into perspective the possible self-reinforcing effects in the adoption path of HT crops, such as increasing farm size, changes in farm equipment, increasing incentives for simplified crop rotations, and the loss of practical knowledge of IWM practices. [ABSTRACT FROM AUTHOR]

Amaranthus palmeri, ranked as the most prolific and troublesome weed in North America, has evolved resistance to several herbicide sites of action. Repeated use of any one herbicide, especially at lower than recommended doses, can lead to evolution of weed resistance, and, therefore, a better understanding of the process of resistance evolution is essential for the management of A. palmeri and other difficult-to-control weed species. Amaranthus palmeri rapidly developed resistance to 4-hydroxyphenylpyruvate dioxygenase (HPPD) inhibitors such as mesotrione. The objective of this study was to test the potential for low-dose applications of mesotrione to select for reduced susceptibility over multiple generations in an A. palmeri population collected from an agricultural field in 2001. F0 plants from the population were initially treated with sub-lethal mesotrione rates and evaluated for survival three weeks after treatment. All F0 plants were controlled at the 1× rate (x = 105 g ai ha−1). However, 2.5% of the F0 plants survived the 0.5× treatment. The recurrent selection process using plants surviving various mesotrione rates was continued until the F4 generation was reached. Based on the GR50 values, the sensitivity index was determined to be 1.7 for the F4 generation. Compared to F0, HPPD gene expression level in the F3 population increased. Results indicate that after several rounds of recurrent selection, the successive generations of A. palmeri became less responsive to mesotrione, which may explain the reduced sensitivity of this weed to HPPD-inhibiting herbicides. The results have significance in light of the recently released soybean and soon to be released cotton varieties with resistance to HPPD inhibitors.

Italian ryegrass (Lolium multiflorum Lam.) can be a troublesome weed that may causes high yield losses to several crops. Ryegrass resistance to the typically used acetolactate synthase (ALS) and acetyl-CoA carboxylase (ACCase) inhibiting herbicides complicates the control. As an alternative, we evaluated and compared the effects of two soil-acting herbicides, flufenacet and prosulfocarb, on susceptible L. multiflorum. The herbicides were applied in two doses in three different methods of applications: (1) soil and foliar application (2) foliar application, and (3) soil application only. Two greenhouse experiments separated in time showed that both herbicides reduced root and foliar biomass significantly as compared to the nontreated plants. In experiment 1, both herbicides resulted in lower efficacy when they only were applied to the leaves compared to the nontreated plants. Especially the foliar effect of flufenacet was small. The highest dose of prosulfocarb (4200 g ai ha−1) reduced the fresh foliar weight by 61% in experiment 1 and by 95% in experiment 2. The lowest dose of prosulfocarb (2100 g ai ha−1) reduced the weights by 73% (experiment 1) and 98% (experiment 2), respectively. For both herbicides the soil and foliar application applied postemergence were effective in reducing growth of L. multiflorum significantly in both experiments. Foliar application showed inconsistent results, showing that soil absorption plays an important role on herbicide efficacy even when the herbicides are applied postemergence. Postemergence application of prosulfocarb and flufenacet were effective to reduce L. multiflorum growth having apparently good root and leaf absorption.

ABSTRACT: Non-target site (NTS) herbicide resistance by degradation enhancement is an increasing problem in several weeds around the world. In this study, the occurrence of degradation enhancement by cytochrome P450 monooxygenases (cytP450) was evaluated as the mechanism of resistance to imazethapyr in barnyardgrass. The cytP450 inhibitors malathion and piperonyl butoxide (PBO) and the inducer naphthalic anhydride (NA), applied in mixture or sequentially with imazethapyr, were evaluated on imidazolinone-susceptible and -resistant barnyardgrass byotipes. In addition, the degradation of imazethapyr was analyzed in plants treated with imazethapyr applied alone or two hours after malathion or NA. The spraying of malathion and PBO reduced the resistance factor (RF) from 15.92 to 3.44 and 4.99, respectively, in the resistant population PALMS01. Conversely, the cytP450 inducer NA increased the RF from 4.45 to 8.32. Malathion increased imazethapyr concentrations in resistant barnyardgrass in comparison with plants sprayed with the herbicide alone, indicating the inhibition of imazethapyr degradation. The simultaneous spraying of malathion and imazethapyr was less efficient than the previous application of this cytP450 inhibitor. These results indicate that degradation enhancement caused by cytP450 enzymes is involved in the resistance mechanism of barnyardgrass to imazethapyr, and appropriate measures should be taken to manage these populations.

Abstract Ten putative resistant and two susceptible Rapistrum rugosum populations originating from Greece were studied for resistance to acetolactate synthase (ALS)-inhibiting herbicides, using dose–response assays, sequencing of als gene and in vitro ALS activity assays. The dose–response assays showed that one (P1) out of ten putative resistant populations was cross-resistant to tribenuron and imazamox, while another population (P4) was resistant to tribenuron only. All populations were susceptible to MCPA at the recommended rate. Gene sequencing of als revealed that the P4 population had a point mutation at Pro197 by His providing resistance to tribenuron, whereas the P1 had a Trp574 by Leu point mutation conferring cross-resistance to tribenuron and imazamox. The in vitro activity of the ALS enzyme indicated I 50 values (tribenuron concentration required for 50% reduction of the ALS activity) ranging from 66.68 to 137.01 μM, whereas the respective value for the S populations ranged from 0.29 to 0.54 μM. These results strongly support that two R. rugosum populations evolved resistance to ALS-inhibiting herbicides due different point mutations in the als gene. Graphical abstract Unlabelled Image Highlights • Rapistrum rugosum populations were resistant to ALS-inhibiting herbicides. • ALS mutation detected at Pro-197 leading to amino acid substitution by His. • ALS mutation detected at Trp-574 leading to amino acid substitution by Leu. • The altered ALS enzyme indicated less-sensitivity to tribenuron. [ABSTRACT FROM AUTHOR]

Highlights • A decision support tool for farmer's strategic thinking. • An activity concept to multi-criteria and multi-scale analyses. • Long rotations increased income but also labor needs. • Crop contracts contributed to the appearance of weeds resistance. Abstract In an uncertain socio-economic and climatic context, sustainable farming is a major challenge for farmers as well as for their agricultural advisors. It is therefore essential to develop a decision support tool (DST) that is likely to be useful to establish and evaluate new production strategies, in accordance with farm sustainability and environmental protection. This paper aims, by using the Agricultural Activity concept, to put forward and test a DST based on mathematical programming used to evaluate strategic production decisions, in conjunction with farmers and agricultural advisors. In the test case, the decisions concern the crop activities and their spatio-temporal combinations in order to reduce both the use of herbicides and the risk of weed resistance to herbicides in cereal-based production systems. Moreover, the DST considers the availability of the workforce during the crop cycle to determine the periods which are likely to require the most significant increase in comparison to the current situation. One scenario showing the current situation (Sc_baseline) and two alternative scenarios have been defined to address the weed-herbicide issue. The comparison of the scenario promoting soil tillage and the introduction of spring crops with Sc_Baseline has shown that the adoption of long-term rotations, the increase in winter crop frequency and the return to deep soil tillage have contributed to an increase in farmer income, total labor and water consumption by 7, 21 and 22% respectively. However, the intensity of pesticide use and nitrate fertilization have dropped by 15% and 17% respectively. By allowing the farmer to establish specific contracts for certain crops, the average income as well as the use of pesticide and nitrate fertilization were increased by at least 10%. This situation is the result of a simplification of rotations with a predominance of winter cereals and the elimination of deep soil tillage. The analysis of these scenarios shows that the use of the DST has made it possible not only to put forward and evaluate alternatives that result in strategic decisions but also to understand, with the concept of Agricultural Activity, the biophysical and technical processes relating to farmer decisions and their impacts at field and farm level. Understanding and sharing this functional chain at farm level is expected to strengthen the farmer-advisor relationship in order to address the complex challenges of farming system sustainability. [ABSTRACT FROM AUTHOR]

The evolution of resistant weed populations in response to intensive herbicide selection pressure is a global issue. Resistance to post-emergence herbicides is widespread, whereas soil-applied pre-emergence herbicides can often remain effective. For example, in Australia pyroxasulfone is a new pre-emergence soil-applied herbicide which provides control of Lolium rigidum populations resistant to multiple post-emergence herbicide modes of action. A fundamental knowledge of the genetic basis of metabolic resistance in weeds is important for understanding plant evolution pathways under herbicide selection and sustaining long-term weed resistance management. In this study we define the mechanistic basis of resistance to pyroxasulfone in a L. rigidum population. TLC provides evidence that pyroxasulfone resistance is metabolism-based with approximately 88% of parental [ 14 C]-labelled pyroxasulfone metabolized in resistant plants 24 h after the herbicide treatment. HPLC-MS allowed identification of several metabolites of pyroxasulfone formed via a glutathione (GSH) conjugation pathway in pyroxasulfone-resistant L. rigidum plants . However, the initial pyroxasulfone-glutathione conjugate was not found likely due to its labile nature. The observed constitutive over-expression from six to nine-fold of two putative resistance-endowing GST genes was associated with the pyroxasulfone resistance phenotype. The most logical conclusion, based on the data thus far available, is that rapid detoxification of pyroxasulfone mediates pyroxasulfone resistance in L. rigidum plants. Future research is warranted to confirm the hypothesis advanced by this study of rapid pyroxasulfone metabolism due to GSH conjugation mediated by GST over-expressed in pyroxasulfone-resistant plants which similarly leads to the production of distinctive GSH-pyroxasulfone metabolites in L. rigidum and wheat. [ABSTRACT FROM AUTHOR]

Field and greenhouse studies investigated the phytoene desaturase (PDS) and photosystem II (PSII)-inhibiting herbicides, norflurazon and metribuzin, as components of two- and three-way postemergence (POST) tank mixtures for controlling multiple herbicide-resistant (MHR) waterhemp (Amaranthus tuberculatus). Studies were conducted at two locations (Champaign County, Illinois, U.S.A (CHR) and McLean County, Illinois, U.S.A. (MCR)) during 2019 and 2020. One of three commercial HPPD-inhibiting herbicides (mesotrione, tembotrione or topramezone) was added to a tank mixture with norflurazon, a reduced rate of metribuzin, or both to determine if greater MHR waterhemp control with tank mixtures could be achieved compared to individual herbicides and assess the potential benefit of norflurazon. Field results indicated the addition of norflurazon to HPPD-inhibiting herbicides resulted in greater waterhemp control (14% increase on average) compared to individual herbicides applied alone. Additionally, metribuzin in combination with HPPD-inhibiting herbicides consistently increased control of MHR waterhemp populations compared to the herbicides applied alone. However, only the three-way tank mixture containing tembotrione at the MCR site reduced biomass relative to two-way treatments containing tembotrione, metribuzin or norflurazon. Greenhouse experiments characterized mixtures of norflurazon with metribuzin and the HPPD-inhibiting herbicides, mesotrione and topramezone. Waterhemp biomass was significantly reduced when metribuzin and HPPD inhibitors were combined in comparison to individual components. Two-way tank mixtures containing norflurazon with mesotrione or metribuzin also resulted in significant biomass reductions compared to herbicides applied alone in MHR waterhemp. However, lower control levels were noted in MHR waterhemp when norflurazon was mixed with either topramezone or topramezone plus metribuzin compared to topramezone alone. In summary, norflurazon and metribuzin can be effective tank mixture components with HPPD-inhibiting herbicides for MHR waterhemp control. However, more research on these tank mixtures is warranted to optimize weed control and crop selectivity, which includes investigating active ingredient ratios, application timings and droplet spectrum effects on coverage. • Multiple herbicide resistance in weeds is an increasing problem in agriculture. • Tank mixtures with herbicides from several site-of-action groups are frequently used. • Tank mixture interactions, such as synergy or antagonism, occasionally occur. • HPPD-inhibiting and PSII-inhibiting herbicides often show synergy on dicot weeds. • Norflurazon exhibited varying interactions with HPPD inhibitor and metribuzin mixes. [ABSTRACT FROM AUTHOR]

Common ragweed emerges early in the season in Nebraska, USA and is competitive with soybean; therefore, preplant herbicides are important for effective control. Glyphosate has been used as a preplant control option; however, confirmation of glyphosate-resistant (GR) common ragweed in Nebraska necessitates evaluating other herbicide options. The objectives of this study were to (1) evaluate the efficacy of preplant (PP) herbicides followed by (fb) glufosinate alone or in tank-mixture with imazethapyr, acetochlor, or S-metolachlor applied post-emergence (POST) for control of GR common ragweed in glufosinate-resistant soybean; (2) their effect on common ragweed density, biomass, and soybean yield; and (3) the partial economics of herbicide programs. A field experiment was conducted in a grower's field infested with GR common ragweed in Gage County, Nebraska, USA in 2015 and 2016. Preplant herbicide programs containing glufosinate, paraquat, 2,4-D, dimethenamid-P, cloransulam-methyl, or high rates of flumioxazin plus chlorimuron-ethyl provided 90–99% control of common ragweed at 21 d after treatment (DAT). The aforementioned PP herbicides fb a POST application of glufosinate alone or in tank-mixture with imazethapyr, acetochlor, or S-metolachlor controlled GR common ragweed 84–98% at soybean harvest, reduced common ragweed density (≤20 plants m−2) and biomass by ≥93%, and secured soybean yield 1,819–2,158 kg ha−1. The PP fb POST herbicide programs resulted in the highest gross profit margins (US$373–US$506) compared to PP alone (US$91) or PRE fb POST programs (US$158). The results of this study conclude that effective and economical control of GR common ragweed in glufosinate-resistant soybean is achievable with PP fb POST herbicide programs.

Annual ryegrass (Lolium multiflorum) and wavy-leaved fleabane (Conyza bonariensis) were tested, aiming to investigate the dose-response of biotypes of both species to glyphosate. Glyphosate herbicide at doses varying from 0 up to 1.440 g e.a. ha-1 was sprayed onto annual ryegrass plants showed four leaves and wavy-leaved fleabane showed three pair of leaves. The fresh weight of shoot was obtained at 21 days after herbicide application. The response of biotypes of L. multiflorum and C. bonariensis to glyphosate was clearly different. For L. multiflorum, the S2, R1, and R3 biotypes supported glyphosate doses 1.5, 3.0, and 8.3 times higher than the biotype S1. For C. bonariensis, the S2 and R biotypes supported glyphosate doses 2.0 and 15.5 times higher than the biotype S1. We found a low glyphosate-resistant (R1) and a high glyphosate-resistant (R2) biotypes of L. multiflorum, in agricultural regions where other biotypes had been found. In addition, a high glyphosate-resistant (R) biotype of C. bonariensis was identified in an agricultural area of Santa Catarina State, Brazil, where weed resistant was not previously found.

The understanding and mitigation of the appearance of herbicide-resistant weeds have come to the forefront of study in the past decade, as the number of weed species that are resistant to one or more herbicide modes of action is on the increase. Historically, weed resistance to auxin herbicides has been rare, but examples, such as Kochia scoparia L. Schrad (kochia), have appeared, posing a challenge to conventional agricultural practices. Reports of dicamba-resistant kochia populations began in the early 1990s in areas where auxin herbicides were heavily utilized for weed control in corn and wheat cropping systems, and some biotypes are resistant to other auxin herbicides as well. We have further characterized the auxin responses of one previously reported dicamba-resistant biotype isolated from western Nebraska and found that it is additionally cross-resistant to other auxin herbicides, including 2,4-dichlorophenoxyacetic acid (2,4-D) and fluroxypyr. We have utilized transcriptome sequencing and comparison to identify a 2-nt base change in this biotype, which results in a glycine to asparagine amino acid change within a highly conserved region of an AUX/indole-3-acetic acid (IAA) protein, KsIAA16. Through yeast two-hybrid analysis, characterization of F2 segregation, and heterologous expression and characterization of the gene in Arabidopsis thaliana, we show that that the single dominant KsIAA16R resistance allele is the causal basis for dicamba resistance in this population. Furthermore, we report the development of a molecular marker to identify this allele in populations and facilitate inheritance studies. We also report that the resistance allele confers a fitness penalty in greenhouse studies. [ABSTRACT FROM AUTHOR]

Non-target site mechanisms are involved in the resistance of sourgrass (Digitaria insularis) to glyphosate. Studies on the 14C-glyphosate absorption and translocation as well as the detection of glyphosate and its metabolites in sourgrass plants were carried out under controlled conditions to investigate if the differential response of resistant sourgrass biotypes (R1 and R2) is derived from the intensity of non-target site mechanisms involved in the resistance to glyphosate. Different pattern of absorption was observed between S (susceptible) and R2 from 12 up to 48 hours after treatment with glyphosate (HAT), and between S and R1 just at 12 HAT. The initial difference in glyphosate absorption among the biotypes did not maintained at 96 HAT and afterwards. Smaller amount of herbicide left the treated leaf into the rest of shoot and roots in R2 (25%) than in S (58%) and R1 (52%). In addition, slight difference in glyphosate translocation was observed between S and R1. We found high percentage (81%) of glyphosate in the S biotype up to 168 HAT, while just 44% and 2% of glyphosate was recovered from R1 and R2 plant tissues. In addition, high percentage of glyphosate metabolites was found in R2 (98%) and R1 (56%) biotypes, while a very low percentage (11%) was found in the S biotype. As previous studies indicated resistant factors of 3.5 and 5.6 for R1 and R2, respectively, we conclude that the differential response of sourgrass biotypes is derived from the intensity of the non-target site mechanisms involved in the resistance to glyphosate.

Rapid detoxification of atrazine in naturally tolerant crops such as maize ( Zea mays) and grain sorghum ( Sorghum bicolor) results from glutathione S-transferase ( GST) activity. In previous research, two atrazine-resistant waterhemp ( Amaranthus tuberculatus) populations from Illinois, U.S.A. (designated ACR and MCR), displayed rapid formation of atrazine-glutathione ( GSH) conjugates, implicating elevated rates of metabolism as the resistance mechanism. Our main objective was to utilize protein purification combined with qualitative proteomics to investigate the hypothesis that enhanced atrazine detoxification, catalysed by distinct GSTs, confers resistance in ACR and MCR. Additionally, candidate Atu GST expression was analysed in an F2 population segregating for atrazine resistance. ACR and MCR showed higher specific activities towards atrazine in partially purified ammonium sulphate and GSH affinity-purified fractions compared to an atrazine-sensitive population ( WCS). One-dimensional electrophoresis of these fractions displayed an approximate 26- kDa band, typical of GST subunits. Several phi- and tau-class GSTs were identified by LC- MS/ MS from each population, based on peptide similarity with GSTs from Arabidopsis. Elevated constitutive expression of one phi-class GST, named Atu GSTF2, correlated strongly with atrazine resistance in ACR and MCR and segregating F2 population. These results indicate that Atu GSTF2 may be linked to a metabolic mechanism that confers atrazine resistance in ACR and MCR. [ABSTRACT FROM AUTHOR]

Common ragweed emerges early in the season in Nebraska, USA and is competitive with soybean; therefore, preplant herbicides are important for effective control. Glyphosate has been used as a preplant control option; however, confirmation of glyphosate-resistant (GR) common ragweed in Nebraska necessitates evaluating other herbicide options. The objectives of this study were to (1) evaluate the efficacy of preplant (PP) herbicides followed by (fb) glufosinate alone or in tank-mixture with imazethapyr, acetochlor, or S-metolachlor applied post-emergence (POST) for control of GR common ragweed in glufosinate-resistant soybean; (2) their effect on common ragweed density, biomass, and soybean yield; and (3) the partial economics of herbicide programs. A field experiment was conducted in a grower's field infested with GR common ragweed in Gage County, Nebraska, USA in 2015 and 2016. Preplant herbicide programs containing glufosinate, paraquat, 2,4-D, dimethenamid-P, cloransulam-methyl, or high rates of flumioxazin plus chlorimuron-ethyl provided 90-99% control of common ragweed at 21 d after treatment (DAT). The aforementioned PP herbicides fb a POST application of glufosinate alone or in tank-mixture with imazethapyr, acetochlor, or S-metolachlor controlled GR common ragweed 84-98% at soybean harvest, reduced common ragweed density (≤20 plants m-2) and biomass by ≥93%, and secured soybean yield 1,819-2,158 kg ha-1. The PP fb POST herbicide programs resulted in the highest gross profit margins (US$373-US$506) compared to PP alone (US$91) or PRE fb POST programs (US$158). The results of this study conclude that effective and economical control of GR common ragweed in glufosinate-resistant soybean is achievable with PP fb POST herbicide programs. [ABSTRACT FROM AUTHOR]