Confirmation of a Three-Way (Glyphosate, ALS, and Atrazine) Herbicide-Resistant Population of Palmer Amaranth (Amaranthus palmeri) in Michigan

Weed Science ◽  
2017 ◽  
Vol 65 (3) ◽  
pp. 327-338 ◽  
Author(s):  
Jonathon R. Kohrt ◽  
Christy L. Sprague ◽  
Satya Swathi Nadakuduti ◽  
David Douches
Keyword(s):  
Copy Number ◽  
Laboratory Experiments ◽  
Fold Increase ◽  
Field Studies ◽  
Palmer Amaranth ◽  
Target Site ◽  
Susceptible Population ◽  
Herbicide Resistant ◽  
Sites Of Action ◽  
Als Inhibitor

The failure of PRE and POST applications of atrazine to control Palmer amaranth in recent field studies prompted further investigation to determine whether this population had evolved resistance to multiple herbicide sites of action, including glyphosate (Group 9), thifensulfuron (Group 2), and atrazine (Group 5). Greenhouse and laboratory experiments were conducted to: (1) confirm the presence of resistance to glyphosate, an ALS inhibitor (thifensulfuron), and atrazine in a single Palmer amaranth population; and (2) establish the molecular basis for resistance to these herbicide sites of action. In the greenhouse, glyphosate+thifensulfuron+atrazine at 1.26 kg ae ha−1+0.0044 kg ai ha−1+1.12 kg ai ha−1provided 55% control of the suspected multiply resistant (MR) Palmer amaranth population and 93% control of the known susceptible population (S). The decreased sensitivity of the MR population compared with the S population at labeled use rates of these herbicides indicated that this population was likely resistant to three different herbicide site of action groups. The RF values for POST applications of glyphosate, thifensulfuron, and atrazine were 12.2, 42.9, and 9.3 times, respectively, for the MR Palmer amaranth population relative to the S population. The RF value for atrazine PRE for the MR population was 112.2 times. Laboratory experiments confirmed that the mechanisms for resistance to ALS-inhibiting herbicides and glyphosate in the MR Palmer amaranth population were target-site based, via amino acid substitution and amplifiedEPSPScopy number, respectively. There was a Pro to Leu substitution at site 197 in the ALS inhibitor–resistant plants, and there was a greater than 50-fold increase inEPSPScopy number in the glyphosate-resistant plants. There were no nucleotide changes in thepsbAgene; therefore, atrazine resistance in this population was not target-site mediated. The evolution of this multiple herbicide-resistant Palmer amaranth population poses significant management challenges to Michigan farmers.

Investigating the resistance levels and mechanisms to penoxsulam and cyhalofop-butyl in barnyardgrass (Echinochloa crus-galli) from Ningxia province, China

Weed Science ◽  
2021 ◽  
pp. 1-25
Author(s):  
Qian Yang ◽  
Xia Yang ◽  
Zichang Zhang ◽  
Jieping Wang ◽  
Weiguo Fu ◽  
...  
Keyword(s):  
Herbicide Resistance ◽  
Molecular Mechanisms ◽  
Acetolactate Synthase ◽  
Rice Fields ◽  
Target Site ◽  
Herbicide Resistant ◽  
Susceptible Populations ◽  
High Level ◽  
Als Inhibitor ◽  
Encoding Genes

Abstract Barnyardgrass (Echinochloa crus-galli) is a noxious grass weed which infests rice fields and causes huge crop yield losses. In this study, we collected twelve E. crus-galli populations from rice fields of Ningxia province in China and investigated the resistance levels to acetolactate synthase (ALS) inhibitor penoxsulam and acetyl-CoA carboxylase (ACCase) inhibitor cyhalofop-butyl. The results showed that eight populations exhibited resistance to penoxsulam and four populations evolved resistance to cyhalofop-butyl. Moreover, all of the four cyhalofop-butyl-resistant populations (NX3, NX4, NX6 and NX7) displayed multiple-herbicide-resistance (MHR) to both penoxsulam and cyhalofop-butyl. The alternative herbicides bispyribac-sodium, metamifop and fenoxaprop-P-ethyl cannot effectively control the MHR plants. To characterize the molecular mechanisms of resistance, we amplified and sequenced the target-site encoding genes in resistant and susceptible populations. Partial sequences of three ALS genes and six ACCase genes were examined. A Trp-574-Leu mutation was detected in EcALS1 and EcALS3 in two high-level (65.84- and 59.30-fold) penoxsulam-resistant populations NX2 and NX10, respectively. In addition, one copy (EcACC4) of ACCase genes encodes a truncated aberrant protein due to a frameshift mutation in E. crus-galli populations. None of amino acid substitutions that are known to confer herbicide resistance were detected in ALS and ACCase genes of MHR populations. Our study reveals the widespread of multiple-herbicide resistant E. crus-galli populations at Ningxia province of China that exhibit resistance to several ALS and ACCase inhibitors. Non-target-site based mechanisms are likely to be involved in E. crus-galli resistance to the herbicides, at least in four MHR populations.

Susceptibility of Palmer amaranth (Amaranthus palmeri) to herbicides in accessions collected from the North Carolina Coastal Plain

Weed Science ◽  
2020 ◽  
Vol 68 (6) ◽  
pp. 582-593
Author(s):  
Denis J. Mahoney ◽  
David L. Jordan ◽  
Nilda Roma-Burgos ◽  
Katherine M. Jennings ◽  
Ramon G. Leon ◽  
...  
Keyword(s):  
North Carolina ◽  
Dose Response ◽  
Coastal Plain ◽  
Weed Management ◽  
Acetolactate Synthase ◽  
Fold Increase ◽  
Palmer Amaranth ◽  
Amaranthus Palmeri ◽  
Sites Of Action ◽  
Two Populations

AbstractPalmer amaranth (Amaranthus palmeri S. Watson) populations resistant to acetolactate synthase (ALS)-inhibiting herbicides and glyphosate are fairly common throughout the state of North Carolina (NC). This has led farm managers to rely more heavily on herbicides with other sites of action (SOA) for A. palmeri control, especially protoporphyrinogen oxidase and glutamine synthetase inhibitors. In the fall of 2016, seeds from A. palmeri populations were collected from the NC Coastal Plain, the state’s most prominent agricultural region. In separate experiments, plants with 2 to 4 leaves from the 110 populations were treated with field use rates of glyphosate, glufosinate-ammonium, fomesafen, mesotrione, or thifensulfuron-methyl. Percent visible control and survival were evaluated 3 wk after treatment. Survival frequencies were highest following glyphosate (99%) or thifensulfuron-methyl (96%) treatment. Known mutations conferring resistance to ALS inhibitors were found in populations surviving thifensulfuron-methyl application (Ala-122-Ser, Pro-197-Ser, Trp-574-Leu, and/or Ser-653-Asn), in addition to a new mutation (Ala-282-Asp) that requires further investigation. Forty-two populations had survivors after mesotrione application, with one population having 17% survival. Four populations survived fomesafen treatment, while none survived glufosinate. Dose–response studies showed an increase in fomesafen needed to kill 50% of two populations (LD50); however, these rates were far below the field use rate (less than 5 g ha−1). In two populations following mesotrione dose–response studies, a 2.4- to 3.3-fold increase was noted, with LD90 values approaching the field use rate (72.8 and 89.8 g ha−1). Screening of the progeny of individuals surviving mesotrione confirmed the presence of resistance alleles, as there were a higher number of survivors at the 1X rate compared with the parent population, confirming resistance to mesotrione. These data suggest A. palmeri resistant to chemistries other than glyphosate and thifensulfuron-methyl are present in NC, which highlights the need for weed management approaches to mitigate the evolution and spread of herbicide-resistant populations.

Evolution of target and non-target based multiple herbicide resistance in a single Palmer amaranth (Amaranthus palmeri) population from Kansas

2020 ◽  
Vol 34 (3) ◽  
pp. 447-453
Author(s):  
Sushila Chaudhari ◽  
Vijay K. Varanasi ◽  
Sridevi Nakka ◽  
Prasanta C. Bhowmik ◽  
Curtis R. Thompson ◽  
...  
Keyword(s):  
Resistance Mechanism ◽  
Acetolactate Synthase ◽  
Palmer Amaranth ◽  
Target Site ◽  
Epsp Synthase ◽  
High Incidence ◽  
Evolution Of Resistance ◽  
Target Site Resistance ◽  
Herbicide Atrazine ◽  
Sites Of Action

AbstractThe evolution of resistance to multiple herbicides in Palmer amaranth is a major challenge for its management. In this study, a Palmer amaranth population from Hutchinson, Kansas (HMR), was characterized for resistance to inhibitors of photosystem II (PSII) (e.g., atrazine), acetolactate synthase (ALS) (e.g., chlorsulfuron), and EPSP synthase (EPSPS) (e.g., glyphosate), and this resistance was investigated. About 100 HMR plants were treated with field-recommended doses (1×) of atrazine, chlorsulfuron, and glyphosate, separately along with Hutchinson multiple-herbicide (atrazine, chlorsulfuron, and glyphosate)–susceptible (HMS) Palmer amaranth as control. The mechanism of resistance to these herbicides was investigated by sequencing or amplifying the psbA, ALS, and EPSPS genes, the molecular targets of atrazine, chlorsulfuron, and glyphosate, respectively. Fifty-two percent of plants survived a 1× (2,240 g ai ha−1) atrazine application with no known psbA gene mutation, indicating the predominance of a non–target site resistance mechanism to this herbicide. Forty-two percent of plants survived a 1× (18 g ai ha−1) dose of chlorsulfuron with proline197serine, proline197threonine, proline197alanine, and proline197asparagine, or tryptophan574leucine mutations in the ALS gene. About 40% of the plants survived a 1× (840 g ae ha−1) dose of glyphosate with no known mutations in the EPSPS gene. Quantitative PCR results revealed increased EPSPS copy number (50 to 140) as the mechanism of glyphosate resistance in the survivors. The most important finding of this study was the evolution of resistance to at least two sites of action (SOAs) (~50% of plants) and to all three herbicides due to target site as well as non–target site mechanisms. The high incidence of individual plants with resistance to multiple SOAs poses a challenge for effective management of this weed.

scholarly journals Effect of dicamba rate and application parameters on protoporphyrinogen oxidase inhibitor-resistant and -susceptible Palmer amaranth (Amaranthus palmeri) control

2020 ◽  
pp. 1-5
Author(s):  
Wyatt Coffman ◽  
Tom Barber ◽  
Jason K. Norsworthy ◽  
Greg R. Kruger
Keyword(s):  
Palmer Amaranth ◽  
Research Station ◽  
Spray Parameters ◽  
Group 14 ◽  
Metabolic Resistance ◽  
Susceptible Population ◽  
Protoporphyrinogen Oxidase ◽  
Sites Of Action ◽  
Carrier Volume ◽  
Nozzle Type

Abstract Throughout eastern Arkansas, Palmer amaranth resistant to protoporphyrinogen oxidase (PPO)-inhibiting herbicides (Group 14 herbicides) has become widespread. Most PPO-resistant Palmer amaranth biotypes possess a target-site mutation, but a metabolic resistance mechanism to fomesafen (Group 14) has also been identified. Once metabolic resistance manifests, plants may also be tolerant to other herbicides and sites of action. To evaluate whether varying spray parameters affected control of PPO-resistant Palmer amaranth in dicamba-tolerant crops, field trials were conducted in 2017 and 2018 at the Lon Mann Cotton Research Station near Marianna, AR, and on-farm in Marion, AR. The experiment included split plot factors of dicamba rate, nozzle type, and carrier volume, with a whole plot factor of population. Dicamba was applied at 560 or 1120 g ae ha−1 through 110015 TTI or AirMix nozzles at 70 or 140 L ha−1 to PPO-resistant or PPO-susceptible Palmer amaranth. Palmer amaranth control 14 d after treatment (DAT) was influenced by an interaction between population and carrier volume. PPO-resistant Palmer amaranth control 14 DAT was 81% regardless of carrier volume, compared with 90% and 95% control at 70 and 140 L ha−1, respectively, of the PPO-susceptible population. An interaction between nozzle type and carrier volume influenced Palmer amaranth control 21 DAT, whereas AirMix nozzles at 140 L ha−1 controlled Palmer amaranth at a greater level (94%) than any other nozzle and carrier volume combination (≤90%). An interaction between population and dicamba rate influenced the relative density of Palmer amaranth 21 DAT. PPO-resistant Palmer amaranth density was less affected by dicamba at either rate than PPO-susceptible Palmer amaranth, relative to the nontreated check. Results concur with those of other research that suggest PPO-resistant Palmer amaranth is harder to control with dicamba. Otherwise, increasing carrier volume affected overall Palmer amaranth control to a greater degree than any other factor.

scholarly journals Evaluation of the time-of-day effect of herbicides applied POST on protoporphyrinogen IX oxidase–resistant and –susceptible Palmer amaranth (Amaranthus palmeri)

2019 ◽  
Vol 33 (5) ◽  
pp. 651-657
Author(s):  
J. Drake Copeland ◽  
Garret B. Montgomery ◽  
Lawrence E. Steckel
Keyword(s):  
Early Morning ◽  
Time Of Day ◽  
Palmer Amaranth ◽  
Amaranthus Palmeri ◽  
Application Time ◽  
Herbicide Resistant ◽  
Consistent Performance ◽  
Sites Of Action ◽  
And Control

AbstractStudies to evaluate the effect of application time of day (TOD) and protoporphyrinogen IX oxidase (PPO)-inhibiting herbicide–resistant Palmer amaranth on the efficacy of commonly used herbicides was conducted in Tennessee in 2017 and 2018. Treatments of fomesafen, lactofen, acifluorfen, paraquat, glufosinate, glufosinate plus fomesafen, paraquat plus fomesafen, and paraquat plus metribuzin were applied to PPO-resistant (PPO-R) and PPO-susceptible (PPO-S) Palmer amaranth at sunrise and midday. Control of Palmer amaranth with acifluorfen, glufosinate, and glufosinate plus fomesafen was greater with the midday application. However, control of Palmer amaranth with paraquat-based treatments was greater with the sunrise application. TOD effects on PPO-inhibiting herbicides and paraquat-based treatments were more prominent for the PPO-R Palmer amaranth biotype. The TOD effect observed when applying glufosinate in early morning hours on PPO-S Palmer amaranth can be minimized by adding fomesafen to the tank mix. However, this strategy did not provide consistent performance on PPO-R Palmer amaranth. The percentages of living Palmer amaranth plants and control were greater when paraquat plus metribuzin was applied to both biotypes. These results highlight the necessity of at least two effective herbicide sites of action for POST applications intended for controlling PPO-R Palmer amaranth. In addition, the timing of herbicide applications can affect their activity in both PPO-R and PPO-S Palmer amaranth populations.

Multiple herbicide–resistant Lolium spp. is prevalent in wheat production in Texas Blacklands

2020 ◽  
Vol 34 (5) ◽  
pp. 652-660 ◽  
Author(s):  
Vijay Singh ◽  
Aniruddha Maity ◽  
Seth Abugho ◽  
James Swart ◽  
David Drake ◽  
...  
Keyword(s):  
Perennial Ryegrass ◽  
Dose Response ◽  
Management Strategies ◽  
Acetolactate Synthase ◽  
Italian Ryegrass ◽  
Susceptible Population ◽  
Wheat Production ◽  
Herbicide Resistant ◽  
Randomized Design ◽  
Als Inhibitor

AbstractField surveys were conducted across the Blacklands region of Texas during 2016 and 2017 to document the distribution of herbicide-resistant Lolium spp. infesting winter wheat production fields in the region. A total of 68 populations (64 Italian ryegrass, four perennial ryegrass) were evaluated in a greenhouse for sensitivity to herbicides of three different modes of action: an acetolactate synthase (ALS) inhibitor (mesosulfuron-methyl), two acetyl-coenzyme-A carboxylase (ACCase) inhibitors (diclofop-methyl and pinoxaden), and a 5-enolpyruvylshikimate-3-phosphate synthase (EPSPS) inhibitor (glyphosate). Herbicides were applied at twice the label-recommended rates for mesosulfuron-methyl (29 g ai ha−1), diclofop-methyl (750 g ai ha−1), and pinoxaden (118 g ai ha−1); and at the recommended rate for glyphosate (868 g ae ha−1). The herbicide screenings were followed by dose-response assays of the most-resistant ryegrass population for each herbicide at eight rates (0.5, 1, 2, 4, 8, 16, 32, and 64×), compared with a susceptible population at six rates (0.0625, 0.125, 0.25, 0.5, 1, and 2×). The initial screening and dose-response experiments were conducted in a completely randomized design with three replications and two experimental runs. Survivors (<80% injury) were characterized as highly resistant (0% to 20% injury) or moderately resistant (21% to 79%). Results showed that 97%, 92%, 39%, and 3% of the Italian ryegrass populations had survivors to diclofop-methyl, mesosulfuron-methyl, pinoxaden, and glyphosate treatments, respectively. Of the four perennial ryegrass populations, three were resistant to diclofop-methyl and mesosulfuron-methyl, and one was resistant to pinoxaden as well. Perennial ryegrass populations did not exhibit any resistance to glyphosate. Dose-response assays revealed 37-, 196-, and 23-fold resistance in Italian ryegrass to mesosulfuron-methyl, diclofop-methyl, and pinoxaden, respectively, compared with a susceptible standard. One Italian ryegrass population exhibited three-way multiple resistance to ACCase-, ALS-, and EPSPS-inhibitors. The proliferation of multiple herbicide–resistant ryegrass is a challenge to sustainable wheat production in Texas Blacklands and warrants diversified management strategies.

scholarly journals Herbicide Program Approaches for Managing Glyphosate-Resistant Palmer Amaranth (Amaranthus palmeri) and Waterhemp (Amaranthus tuberculatusandAmaranthus rudis) in Future Soybean-Trait Technologies

2015 ◽  
Vol 29 (4) ◽  
pp. 716-729 ◽  
Author(s):  
Christopher J. Meyer ◽  
Jason K. Norsworthy ◽  
Bryan G. Young ◽  
Lawrence E. Steckel ◽  
Kevin W. Bradley ◽  
...  
Keyword(s):  
Palmer Amaranth ◽  
Amaranthus Palmeri ◽  
Single Experiment ◽  
Herbicide Resistant ◽  
Synthetic Auxin ◽  
Wide Range ◽  
Soybean Genetics ◽  
Sites Of Action ◽  
Herbicide Programs ◽  
Weed Emergence

Herbicide-resistantAmaranthusspp. continue to cause management difficulties in soybean. New soybean technologies under development, including resistance to various combinations of glyphosate, glufosinate, dicamba, 2,4-D, isoxaflutole, and mesotrione, will make possible the use of additional herbicide sites of action in soybean than is currently available. When this research was conducted, these soybean traits were still regulated and testing herbicide programs with the appropriate soybean genetics in a single experiment was not feasible. Therefore, the effectiveness of various herbicide programs (PRE herbicides followed by POST herbicides) was evaluated in bare-ground experiments on glyphosate-resistant Palmer amaranth and glyphosate-resistant waterhemp (both tall and common) at locations in Arkansas, Illinois, Indiana, Missouri, Nebraska, and Tennessee. Twenty-five herbicide programs were evaluated; 5 of which were PRE herbicides only, 10 were PRE herbicides followed by POST herbicides 3 to 4 wks after (WA) the PRE application (EPOST), and 10 were PRE herbicides followed by POST herbicides 6 to 7 WA the PRE application (LPOST). Programs with EPOST herbicides provided 94% or greater control of Palmer amaranth and waterhemp at 3 to 4 WA the EPOST. Overall, programs with LPOST herbicides resulted in a period of weed emergence in which weeds would typically compete with a crop. Weeds were not completely controlled with the LPOST herbicides because weed sizes were larger (≥ 15 cm) compared with their sizes at the EPOST application (≤ 7 cm). Most programs with LPOST herbicides provided 80 to 95% control at 3 to 4 WA applied LPOST. Based on an orthogonal contrast, using a synthetic-auxin herbicide LPOST improves control of Palmer amaranth and waterhemp over programs not containing a synthetic-auxin LPOST. These results show herbicides that can be used in soybean and that contain auxinic- or HPPD-resistant traits will provide growers with an opportunity for better control of glyphosate-resistant Palmer amaranth and waterhemp over a wide range of geographies and environments.

PRE herbicides influence critical time of weed removal in glyphosate-resistant corn

2020 ◽  
pp. 1-8
Author(s):  
Ayse Nur Ulusoy ◽  
O. Adewale Osipitan ◽  
Jon Scott ◽  
Amit J. Jhala ◽  
Nevin C. Lawrence ◽  
...  
Keyword(s):  
Weed Management ◽  
Growth Stage ◽  
Critical Time ◽  
Maximum Growth ◽  
Field Studies ◽  
Growth Stages ◽  
Herbicide Resistant ◽  
Main Plot ◽  
Sites Of Action ◽  
Weed Removal

Abstract Residual herbicides applied PRE provide early season weed control, potentially avoid the need for multiple POST herbicides, and can provide additional control of herbicide-resistant weeds. Thus, field studies were conducted in 2017 and 2018 at Concord, NE, to evaluate the influence of PRE herbicides on critical time for postemergence weed removal (CTWR) in corn. The studies were arranged in a split-plot design that consisted of three herbicide regimes as main plot treatments and seven weed removal timings as subplot treatments in four replications. The herbicide regimes included no PRE herbicide, atrazine, and a premix of saflufenacil/dimethenamid-P mixed with pyroxasulfone. The weed removal timings were at V3, V6, V9, V12, and V15 corn growth stages and then plots were kept weed-free until harvest. A weed-free and nontreated control were included for comparison. The relationship between corn growth or yield, and weed removal timings in growing degree days (GDD) was described by a four-parameter log-logistic model. This model was used to estimate the critical time for weed removal based on 5% crop yield loss threshold. A delay in weed removal until the V2 to V3 corn growth stage (91 to 126 GDD) reduced corn biomass by 5% without PRE herbicide application. The CTWR started at V3 without PRE herbicide in both years. Atrazine delayed the CTWR up to V5 in both years, whereas saflufenacil/dimethenamid-P plus pyroxasulfone further delayed the CTWR up to the V10 and V8 corn growth stages in 2017 and 2018, respectively. Herbicide applied PRE particularly with multiple sites of action can delay the CTWR in corn up to a maximum growth stage of V10, and delay or reduce the need for POST weed management.

Acetolactate Synthase (ALS) Target-Site Mutations in ALS Inhibitor-Resistant Russian Thistle (Salsola tragus)

Weed Science ◽  
2010 ◽  
Vol 58 (3) ◽  
pp. 244-251 ◽  
Author(s):  
Suzanne I. Warwick ◽  
Connie A. Sauder ◽  
Hugh J. Beckie
Keyword(s):  
Molecular Basis ◽  
Genome Structure ◽  
Acetolactate Synthase ◽  
Molecular Techniques ◽  
Target Site ◽  
Weed Species ◽  
Single Nucleotide ◽  
Herbicide Resistant ◽  
Inhibitor Resistance ◽  
Als Inhibitor

ALS inhibitor-resistant biotypes are the fastest growing class of herbicide-resistant (HR) weeds. A Canadian ALS inhibitor-resistant biotype of Russian thistle was first reported in 1989. The molecular basis for ALS-inhibitor resistance is unknown for Canadian populations of this polyploid weed species, and was determined in this study for one Alberta and two Saskatchewan HR Russian thistle populations. HR plants survived spray application of the ALS-inhibitor mixture thifensulfuron : tribenuron in the greenhouse. All three HR Russian thistle populations were heterogeneous and contained both HR and herbicide-susceptible (HS) individuals. The molecular basis for resistance was determined by sequencing theALSgene and/or conducting a TaqMan genotyping assay for single nucleotide polymorphism (SNP) for the Trp574Leu mutation. Two target-site mutations were observed: Trp574Leu in all three biotypes (554 individuals) and Pro197Gln in one biotype (one individual), suggesting multiple-founding events for Russian thistle HR populations in western Canada. Segregation patterns among F1 and F2 progeny arrays of HR lines sprayed under greenhouse conditions varied; some segregated (i.e., had HR and HS progeny), whereas other lines were exclusively HR. In contrast, no segregation of molecular types, i.e., Trp574, Trp/Leu574and Leu574, as would be expected with heterozygosity at a single locus Trp/Leu574, was observed. Such lack of segregation is consistent with the polyploid genome structure of Russian thistle and the presence of two copies of theALSgene. The presence of more than oneALSgene confounded the ability of the molecular techniques to accurately identify “true” heterozygotes in this study.

Varying responses of field-selected herbicide-resistant rigid ryegrass (Lolium rigidum) populations to combinations of phorate with PPI herbicides

Weed Science ◽  
2020 ◽  
Vol 68 (4) ◽  
pp. 367-372
Author(s):  
David J. Brunton ◽  
Peter Boutsalis ◽  
Gurjeet Gill ◽  
Christopher Preston
Keyword(s):  
Fold Increase ◽  
Acid Synthesis ◽  
Resistance Mechanisms ◽  
Lolium Rigidum ◽  
Cytochrome P450 Enzymes ◽  
Long Chain Fatty Acid ◽  
Herbicide Resistant ◽  
Rigid Ryegrass ◽  
Sites Of Action

AbstractOrganophosphate insecticides, which have the capacity to inhibit specific herbicide-degrading (cytochrome P450) enzymes, have been used to explore metabolic herbicide-resistance mechanisms in weeds. This study investigates the response of seven field-selected rigid ryegrass (Lolium rigidum Gaudin) populations to herbicides from three different sites of action in the presence or absence of the P450 inhibitor phorate. Phorate antagonized the thiocarbamate herbicides triallate and prosulfocarb (8-fold increase in LD50) in multiple resistant L. rigidum populations with resistance to three different site-of-action herbicides. In contrast, phorate synergized trifluralin and propyzamide in some populations, reducing the LD50 by 50%. Conversely, treatment with phorate had no significant effect on the LD50 for S-metolachlor or pyroxasulfone (inhibitors of very-long-chain fatty-acid synthesis). Phorate has diverse effects that are herbicide and population dependant in field-selected L. rigidum, suggesting P450 involvement in the metabolism of trifluralin and failure to activate thiocarbamate herbicides in these populations. This research highlights the need for implementation of diverse approaches other than herbicide alone as part of a long-term integrated strategy to reduce the likelihood of metabolism-based resistance to PPI herbicides in L. rigidum.

Sign in / Sign up

Export Citation Format

Share Document