Herbicides classified as synthetic auxins have been most commonly used to control broadleaf weeds in a variety of crops and in non‐cropland areas since the first synthetic auxin herbicide (SAH
Herbicides classified as synthetic auxins have been most commonly used to control broadleaf weeds in a variety of crops and in non‐cropland areas since the first synthetic auxin herbicide (SAH), 2,4‐D, was introduced to the market in the mid‐1940s. The incidence of weed species resistant to SAHs is relatively low considering their long‐term global application with 30 broadleaf, 5 grass, and 1 grass‐like weed species confirmed resistant to date. An understanding of the context and mechanisms of SAH resistance evolution can inform management practices to sustain the longevity and utility of this important class of herbicides. A symposium was convened during the 2nd Global Herbicide Resistance Challenge (May 2017; Denver, CO, USA) to provide an overview of the current state of knowledge of SAH resistance mechanisms including case studies of weed species resistant to SAHs and perspectives on mitigating resistance development in SAH‐tolerant crops. ? 2017 The Authors.
Pest Management Science
published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.
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BACKGROUND Lolium rigidum is the weed of greatest economic impact in Australia due to its formidable capacity to evolve herbicide resistance. In this study, 579 field-sampled L. rigidum populations were tested for resistance to 21...
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BACKGROUND Lolium rigidum is the weed of greatest economic impact in Australia due to its formidable capacity to evolve herbicide resistance. In this study, 579 field-sampled L. rigidum populations were tested for resistance to 21 herbicides applied at the recommended rate. Nine herbicide treatments were binary mixtures. RESULTS A total of 15 876 individual resistance tests were conducted by screening two million seeds at the recommended label rate. The overall frequency of resistant populations was 31%, 14%, 71%, 6% and 0% in response to the post-emergence herbicide treatments clethodim, clethodim + butroxydim, imazamox + imazapyr, glyphosate and paraquat, respectively. The resistance frequency to stand-alone pre-emergence wheat-selective herbicides ranged from 10% to 34%. Conversely, the levels of resistance to pre-emergence mixtures or stand-alone propyzamide were significantly lower, ranging from 6% to 0%. In winter, the responses to glyphosate, paraquat, cinmethylin, prosulfocarb, pyroxasulfone and trifluralin were reassessed, with 7%, 0%, 0%, 21%, 21% and 28% as the respective resistance frequencies. South Australia and Victoria are identified as epicenters for L. rigidum population resistance to pyroxasulfone, whereas populations in New South Wales have the greatest resistance to glyphosate and in Western Australia to clethodim. CONCLUSIONS For the first time, resistance levels to stand-alone herbicides and binary mixtures are geographically ranked across the Australian continent by benchmark statistical analysis of resistance frequencies and distribution. The extension of these results will raise awareness of rapidly emerging patterns of herbicide resistance, encouraging the adoption of cost-effective modes of action and integration of diverse strategies for weed resistance management.
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Flumioxazin and fomesafen are commonly used to control glyphosate-resistant Palmer amaranth in cotton and other crops, thus increasing risk to select for Palmer amaranth biotypes resistant to protoporphyrinogen oxidase (PPO) inhib...
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Flumioxazin and fomesafen are commonly used to control glyphosate-resistant Palmer amaranth in cotton and other crops, thus increasing risk to select for Palmer amaranth biotypes resistant to protoporphyrinogen oxidase (PPO) inhibitors. A field experiment was conducted to determine the potential for fluridone and acetochlor to substitute for soil-applied PPO inhibitors in a Palmer amaranth management system with glufosinate applied twice POST and diuron plus MSMA POST-directed in conservation tillage cotton. Fluridone and flumioxazin applied preplant 23 to 34 d prior to planting were similarly effective. Fluridone and acetochlor plus diuron applied PRE controlled Palmer amaranth as well as fomesafen plus diuron PRE. All systems with preplant and PRE herbicides followed by glufosinate POST and diuron plus MSMA layby controlled Palmer amaranth well. Cotton yield did not differ among herbicide treatments. This research demonstrates that fluridone and acetochlor can substitute for soil-applied PPO-inhibiting herbicides in management systems for Palmer amaranth.
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Seeds of a suspected glyphosate-resistant giant ragweed biotype from Lauderdale County, TN, were collected from a continuous cotton field in fall 2007 after plants were nonresponsive to multiple glyphosate applications. The object...
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Seeds of a suspected glyphosate-resistant giant ragweed biotype from Lauderdale County, TN, were collected from a continuous cotton field in fall 2007 after plants were nonresponsive to multiple glyphosate applications. The objectives of this research were to (1) confirm resistance by quantifying the response of the putative resistant biotype to glyphosate compared to a susceptible biotype from a nonagricultural area, (2) quantify shikimate accumulation over time in both biotypes, and (3) determine the effectiveness of POST-applied herbicides labeled for use in cotton in controlling both biotypes at three growth stages. The susceptible biotype had a 50% lethal dose of 407 g ae/ha of glyphosate compared with 2,176 g/ha for the resistant biotype when treated at the four-node stage, a 5.3-fold level of resistance. The resistant biotype accumulated 3.3- to 9.8-fold less shikimate than the susceptible biotype at 1 to 7 d after treatment. The resistant biotype was less responsive to glyphosate as treatment was delayed past the two-node stage, much more than the susceptible biotype. Glufosinate, MSMA, and diuron controlled both biotypes by at least 90%, regardless of size at application. Prometryn, flumioxazin, carfentrazone-ethyl, fomesafen, and trifloxysulfuron controlled both biotypes by at least 89% when applied at the two-node stage, but control generally diminished with later application timings. Pyrithiobac was not effective in controlling either biotype, regardless of size at application. Hence, there are effective herbicide options for controlling glyphosate-resistant giant ragweed in cotton, and the resistant biotype does not appear to exhibit multiple resistances to other herbicides.
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The first case of resistance to sulfonylurea herbicides reported in Switzerland is discussed. It concerns a biotype of loosy silky-bent (Apera spica-venti) which is considered as one of the most serious grass weed infesting arable...
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The first case of resistance to sulfonylurea herbicides reported in Switzerland is discussed. It concerns a biotype of loosy silky-bent (Apera spica-venti) which is considered as one of the most serious grass weed infesting arable fields in Switzerland. The exact level and amplitude of this resistance, as well as its mechanism and genetics, still need to be specified, however, preliminary results unambiguously demonstrate its existence. Currently, strict implementation of the rules aiming to avoid further development of this resistance in fields infested by A. spica-venti is justified..
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Herbicides control undesired grasses and weeds while leaving the crop relatively unharmed. Herbicide antidotes (safeners) protect crops from herbicide damage without protecting weeds. Resistance to herbicides means the survival of...
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Herbicides control undesired grasses and weeds while leaving the crop relatively unharmed. Herbicide antidotes (safeners) protect crops from herbicide damage without protecting weeds. Resistance to herbicides means the survival of a segment of the population following treatment with an herbicide dosage lethal to the normal population. Three mechanisms that account for herbicide resistance are: alterations in the target site, enhanced metabolism and compartmentation of the herbicide. Plants metabolizemost herbicides through a series of intermediates ultimately to non toxic compounds. The basic detoxification reactions are oxidation, reduction, hydrolysis and conjugation. Major oxidative reactions are catalyzed by Cytochrome P450 monooxygenases (P450s) while the enzymatic conjugation with glutathione (GSH) catalyzed by glutathione S-transferases (GSTs) is the major detoxification pathway. Resistance occurs in plants as the result of random and infrequent mutations. Cross-resistance refers to resistance to an herbicide the plant has not been previously exposed to but that has a mode of action similar to the original herbicide. Multiple-resistance refers to resistance to more than one class of herbicides with very different modes of action. Most of uses of molecular biology are to find new herbicide targets and to generate herbicide-resistant crops by inserting exogenous resistance genes into the crops or by selecting natural mutations. Unlike the generation of transgenics, recurrent selection of anatural mutant will select for homozygous resistant individuals. Transgenics bear and express both the native and transgenic enzymes; they are functionally heterozygous and will remain so. Nevertheless, precautions must be considered for risk assessment.The main risk is claimed to be that of the biotechnologically-derived herbicide resistant crops becoming 'volunteer' weeds, or their introgressing traits into a wild relatives. The final decision on risk/benefit is ultimately a balance between science,economics, local benefits, local values, pressure groups and local politics.
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Herbicides control undesired grasses and weeds while leaving the crop relativelyunharmed. Herbicide antidotes (safeners) protect crops from herbicide damage withoutprotecting weeds. Resistance to herbicides means the survival of a...
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Herbicides control undesired grasses and weeds while leaving the crop relativelyunharmed. Herbicide antidotes (safeners) protect crops from herbicide damage withoutprotecting weeds. Resistance to herbicides means the survival of a segment of the populationfollowing treatment with an herbicide dosage lethal to the normal population Threemechanisms that account for herbicide resistance are: alterations in the target site, enhancedmetabolism and compartmentation of the herbicide. Plants metabolize most herbicidesthrough a series of intermediates ultimately to non toxic compounds. The basic detoxificationreactions are oxidation, reduction, hydrolysis and conjugation. Major oxidative reactions arecatalyzed by Cytochrome P450 monooxygenases (P450s) while the enzymatic conjugationwith glutathione (GSH) catalyzed by glutathione S-transferases (GSTs) is the majordetoxification pathway. Resistance occurs in plants as the result of random and infrequentmutations.Cross-resistance refers to resistance to an herbicide the plant has not beenpreviously exposed to but that has a mode of action similar to the original herbicide.Multiple-resistance refers to resistance to more than one class of herbicides with verydifferent modes of action. Most of uses of molecular biology are to find new herbicidetargets and to generate herbicide-resistant crops by inserting exogenous resistance genes intothe crops or by selecting natural mutations. Unlike the generation of transgenics, recurrentselection of a natural mutant will select for homozygous resistant individuals. Transgenicsbear and express both the native and transgenic enzymes; they are functionally heterozygousand will remain so. Nevertheless, precautions must be considered for risk assessment. Themain risk is claimed to be that of the biotechnologically-derived herbicide resistant cropsbecoming 'volunteer’weeds,or their introgressing traits into a wild relatives. The finaldecision on risk/benefit is ultimately a balance between science, economics, local benefits,local values, pressure groups and local politics.
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Glyphosate has performed long and well, but now some weed communities are shifting to populations that survive glyphosate, and growers need new weed management technologies to augment glyphosate performance in glyphosate-resistant...
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Glyphosate has performed long and well, but now some weed communities are shifting to populations that survive glyphosate, and growers need new weed management technologies to augment glyphosate performance in glyphosate-resistant crops. Unfortunately, most companies are not developing any new selective herbicides with new modes of action to fill this need. Fortunately, companies are developing new herbicide-resistant crop technologies to combine with glyphosate resistance and expand the utility of existing herbicides. One of the first multiple-herbicide-resistant crops will have a molecular stack of a new metabolically based glyphosate resistance mechanism with an active-site-based resistance to a broad spectrum of ALS-inhibiting herbicides. Additionally, new formulation technology called homogeneous blends will be used in conjunction with glyphosate and ALS-resistant crops. This formulation technology satisfies governmental regulations, so that new herbicide mixture offerings with diverse modes of action can be commercialized more rapidly and less expensively. Together, homogeneous blends and multiple-herbicide-resistant crops can offer growers a wider choice of herbicide mixtures at rates and ratios to augment glyphosate and satisfy changing weed management needs.
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BACKGROUND: A survey of 400 growers of maize, soybeans and cotton was made in the United States to determine perceptions, experiences and management practices with glyphosate-resistant weeds. The survey included growers in the nor...
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BACKGROUND: A survey of 400 growers of maize, soybeans and cotton was made in the United States to determine perceptions, experiences and management practices with glyphosate-resistant weeds. The survey included growers in the north (corn belt) and south (cotton belt) of the USA in spring 2006. RESULTS: Interestingly, 24 and 39% of northern and southern growers, respectively, assumed they had glyphosate weed resistance on their farm. Of the 200 southern growers interviewed, 67% had planted continuous glyphosate-resistant (GR) crops for a period of 3-5 years. According to the survey respondents, the key method for managing glyphosate-resistant weeds was to rotate to other herbicides. CONCLUSION: Growers do value GR crop technology but are adopting measures to manage resistance only as needed.
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