Herbicide strategies for managing glyphosate-resistant and susceptible kochia (Bassia scoparia) in spring wheat

Kochia [<i>Bassia scoparia</i> (L.) A.J. Scott] is a summer-annual tumbleweed that is tolerant of heat, drought and salinity, and capable of causing large yield losses in spring wheat (<i>Triticum aestivum</i> L). Increased incidence of glyphosate and acetolactate synthase (ALS) inhibitor-resistant kochia in Western Canada warrants investigation of alternative herbicides to manage these biotypes. Herbicides applied pre- or post-emergence in spring wheat were evaluated based on crop tolerance and control of ALS inhibitor-resistant kochia accessions with and without the glyphosate resistance trait in five environments near Lethbridge and Coalhurst, Alberta, from 2013-2015. The most effective and consistent treatments for kochia management included sulfentrazone applied pre-emergence, and fluroxypyr/bromoxynil/2,4-D or pyrasulfotole/bromoxynil applied post-emergence. All of these treatments resulted in ≥ 90% visible control in all environments and ≥ 90% kochia biomass reduction compared with the untreated control in Lethbridge 2014 and 2015. MCPA/dichlorprop-p/mecoprop-p, dicamba/2,4-D/mecoprop-p, and dicamba/fluroxypyr resulted in acceptable control among environments (≥ 80% visible control in all environments and ≥ 80% kochia biomass reduction in Lethbridge 2014 and 2015); however the latter two options caused unacceptable (> 10%) wheat visible injury in Coalhurst 2014. Recent confirmations of auxinic herbicide-resistant kochia in Western Canada – due, in part, to use of synthetic auxins to manage glyphosate-resistant kochia in small-grain cereals – will limit kochia management options. When implemented with non-chemical tools as part of an integrated weed management program, alternative herbicide modes of action like protoporphyrinogen oxidase inhibitors before and photosystem II or 4-hydroxyphenylpyruvate dioxygenase inhibitor(s) within spring wheat could mitigate selection for multiple herbicide-resistant kochia.

Download Full-text

Pollen- and Seed-Mediated Gene Flow in Kochia (Kochia scoparia)

Weed Science ◽

10.1614/ws-d-16-00038.1 ◽

2016 ◽

Vol 64 (4) ◽

pp. 624-633 ◽

Cited By ~ 21

Author(s):

Hugh J. Beckie ◽

Robert E. Blackshaw ◽

Linda M. Hall ◽

Eric N. Johnson

Keyword(s):

Gene Flow ◽

Acetolactate Synthase ◽

Western Canada ◽

Kochia Scoparia ◽

Hub And Spoke ◽

Herbicide Resistant ◽

Prevailing Wind Direction ◽

Seed Mediated ◽

Als Inhibitor ◽

Natural Dispersal

Efficient natural dispersal of herbicide-resistance alleles via seed and pollen can markedly accelerate the incidence of herbicide-resistant weed populations across an agroecoregion. Studies were conducted in western Canada in 2014 and 2015 to investigate pollen- and seed-mediated gene flow in kochia. Pollen-mediated gene flow (PMGF) from glyphosate-resistant (GR) to non-GR kochia was quantified in a field trial (hub and spoke design) at Saskatoon, Saskatchewan. Seed-mediated gene flow of acetolactate synthase (ALS) inhibitor-resistant kochia as a function of tumbleweed speed and distance was estimated in cereal stubble fields at Lethbridge, Alberta and Scott, Saskatchewan. Regression analysis indicated that outcrossing from GR to adjacent non-GR kochia ranged from 5.3 to 7.5%, declining exponentially to 0.1 to 0.4% at 96 m distance. However, PMGF was significantly influenced by prevailing wind direction during pollination (maximum of 11 to 17% outcrossing down-wind). Seed dropped by tumbleweeds varied with distance and plant speed, approaching 90% or more (ca. 100,000 seeds or more) at distances of up to 1,000 m and plant speeds of up to 300 cm s–1. This study highlights the efficient proximal (pollen) and distal (seed) gene movement of this important GR weed.

Download Full-text

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

Weed Science ◽

10.1017/wsc.2021.37 ◽

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.

Download Full-text

Evaluation of Florpyrauxifen-benzyl on Herbicide-Resistant and Herbicide-Susceptible Barnyardgrass Accessions

Weed Technology ◽

10.1017/wet.2017.100 ◽

2017 ◽

Vol 32 (2) ◽

pp. 126-134 ◽

Cited By ~ 3

Author(s):

M. Ryan Miller ◽

Jason K. Norsworthy ◽

Robert C. Scott

Keyword(s):

Plant Height ◽

Mechanism Of Action ◽

Control Plant ◽

Resistance Management ◽

Acetolactate Synthase ◽

Management Tool ◽

Alternative Mechanism ◽

Alternative Mode ◽

Herbicide Resistant ◽

Biomass Reduction

AbstractFlorpyrauxifen-benzyl is a new herbicide under development in rice that will provide an alternative mode of action to control barnyardgrass. Multiple greenhouse experiments evaluated florpyrauxifen-benzyl efficacy on barnyardgrass accessions collected in rice fields across Arkansas, and to evaluate its efficacy on herbicide-resistant biotypes. In one experiment, florpyrauxifen-benzyl was applied at the labeled rate of 30 g ai ha−1to 152 barnyardgrass accessions collected from 21 Arkansas counties. Florpyrauxifen-benzyl at 30 g ai ha−1effectively controlled barnyardgrass and subsequently reduced plant height and aboveground biomass. In a dose-response experiment, susceptible-, acetolactate synthase (ALS)-, propanil-, and quinclorac-resistant barnyardgrass biotypes were subjected to nine rates of florpyrauxifen-benzyl ranging from 0 to 120 g ai ha−1. The effective dose required to provide 90% control, plant height reduction, and biomass reduction of the susceptible and resistant biotypes fell below the anticipated labeled rate of 30 g ai ha−1. Based on these results, quinclorac-resistant barnyardgrass as well as other resistant biotypes can be controlled with florpyrauxifen-benzyl at 30 g ai ha−1. Overall, results from these studies indicate that florpyrauxifen-benzyl can be an effective tool for controlling susceptible and currently existing herbicide-resistant barnyardgrass biotypes in rice. Additionally, the unique auxin chemistry of florpyrauxifen-benzyl will introduce an alternative mechanism of action in rice weed control thus acting as an herbicide-resistance management tool.

Download Full-text

Glyphosate- and acetolactate synthase inhibitor-resistant kochia (Bassia scoparia) control in field pea

Canadian Journal of Plant Science ◽

10.1139/cjps-2021-0178 ◽

2021 ◽

Author(s):

Alysha T Torbiak ◽

Robert Blackshaw ◽

Randall N Brandt ◽

Bill Hamman ◽

Charles M. Geddes

Keyword(s):

Great Plains ◽

Field Experiments ◽

Rapid Evolution ◽

Acetolactate Synthase ◽

Field Pea ◽

Visible Injury ◽

Crop Harvest ◽

Selection For ◽

Synthase Inhibitor ◽

Als Inhibitor

Kochia [Bassia scoparia (L.) A.J. Scott] is an invasive C4 tumbleweed in the Great Plains of North America, where it impedes crop harvest and causes significant crop yield losses. Rapid evolution and spread of glyphosate- and acetolactate synthase (ALS) inhibitor-resistant kochia in western Canada limit the herbicide options available for control of these biotypes in field pea (Pisum sativum L.); one of the predominant pulse crops grown in this region. Field experiments were conducted near Lethbridge, Alberta in 2013-2015 and Coalhurst, Alberta in 2013-2014 to determine which herbicide options effectively control glyphosate- and ALS inhibitor-resistant kochia in field pea. Visible injury of field pea was minor (0-4%) in all environments except for Lethbridge 2013, where pre-plant (PP) flumioxazin and all treatments containing post-emergence (POST) imazamox/bentazon resulted in unacceptable (14-23%) pea visible injury. Herbicide impacts on pea yield were minor overall. Carfentrazone + sulfentrazone PP and saflufenacil PP followed by imazamox/bentazon POST resulted in ≥80% visible control of kochia in all environments, while POST imazamox/bentazon alone resulted in ≥80% reduction in kochia biomass in all environments compared with the untreated control (albeit absent of statistical difference in Coalhurst 2014). These results suggest that layering the protoporhyrinogen oxidase-inhibiting herbicides saflufenacil or carfentrazone + sulfentrazone PP with the ALS- and photosystem II-inhibiting herbicide combination imazamox/bentazon POST can effectively control glyphosate- and ALS inhibitor-resistant kochia in field pea while also mitigating further selection for herbicide resistance through the use of multiple effective herbicide modes-of-action.

Download Full-text

Glyphosate- and Acetolactate Synthase Inhibitor–Resistant Kochia (Kochia scoparia) in Western Canada

Weed Science ◽

10.1614/ws-d-12-00140.1 ◽

2013 ◽

Vol 61 (2) ◽

pp. 310-318 ◽

Cited By ~ 50

Author(s):

Hugh J. Beckie ◽

Robert E. Blackshaw ◽

Ryan Low ◽

Linda M. Hall ◽

Connie A. Sauder ◽

...

Keyword(s):

Dose Response ◽

Best Management Practices ◽

Management Practices ◽

Acetolactate Synthase ◽

Glyphosate Resistance ◽

Western Canada ◽

Wild Oat ◽

Green Foxtail ◽

Inhibitor Resistance ◽

Als Inhibitor

In summer, 2011, we investigated suspected glyphosate-resistant (GR) kochia in three chem-fallow fields (designated F1, F2, F3, each farmed by a different grower) in southern Alberta. This study characterizes glyphosate resistance in those populations, based on data from dose–response experiments. In a greenhouse experiment, the three populations exhibited a resistance factor ranging from 4 to 6 based on shoot biomass response (GR50ratios), or 5 to 7 based on survival response (LD50ratios). Similar results were found in a field dose–response experiment at Lethbridge, AB, in spring 2012 using the F2 kochia population. In fall 2011, we surveyed 46 fields within a 20-km radius of the three chem-fallow fields for GR kochia. In the greenhouse, populations were screened with glyphosate at 900 g ae ha−1. Seven populations were confirmed as GR, the farthest site located about 13 km from the three originally confirmed populations. An additional GR population more than 100 km away was later confirmed. Populations were screened for acetolactate synthase (ALS)–inhibitor (thifensulfuron : tribenuron) and dicamba resistance in the greenhouse, with molecular characterization of ALS-inhibitor resistance in the F1, F2, and F3 populations. All GR populations were resistant to the ALS-inhibiting herbicide, but susceptible to dicamba. ALS-inhibitor resistance in kochia was conferred by Pro197, Asp376, or Trp574amino acid substitutions. Based upon a simple empirical model with a parameter for selection pressure, calculated from weed relative abundance and glyphosate efficacy, and a parameter for seedbank longevity, kochia, wild oat, and green foxtail were the top three weeds, respectively, predicted at risk of selection for glyphosate resistance in the semiarid Grassland region of the Canadian prairies; wild oat, green foxtail, and cleavers species were predicted at greatest risk in the subhumid Parkland region. This study confirms the first occurrence of a GR weed in western Canada. Future research on GR kochia will include monitoring, biology and ecology, fitness, mechanism of resistance, and best management practices.

Download Full-text

Effectiveness of Herbicides for Control of Hairy Vetch (Vicia villosa) in Winter Wheat

Weed Technology ◽

10.1614/wt-d-14-00139.1 ◽

2015 ◽

Vol 29 (3) ◽

pp. 509-518 ◽

Cited By ~ 11

Author(s):

William S. Curran ◽

John M. Wallace ◽

Steven Mirsky ◽

Benjamin Crockett

Keyword(s):

Winter Wheat ◽

Weed Management ◽

Acetolactate Synthase ◽

Oxidase Inhibitor ◽

Management Program ◽

Integrated Weed Management ◽

Hairy Vetch ◽

Synthetic Auxins ◽

Als Inhibitors ◽

Tribenuron Methyl

A field experiment was conducted in 2009–2010 at Pennsylvania and Maryland locations, and repeated it in 2010–2011 to test the effectiveness of POST-applied herbicides at fall and spring timings on seeded hairy vetch in winter wheat. A total of 16 herbicide treatment combinations was tested that included synthetic auxins, acetolactate synthase (ALS) inhibitors, and a protoporphyrinogen oxidase inhibitor. Spring applications tended to be more effective than fall applications. Among synthetic auxins, clopyralid (105 g ae ha−1) and treatments containing dicamba (140 g ae ha−1) were effective at both timings, resulting in greater than 90% hairy vetch control at wheat harvest. Pyroxsulam and prosulfuron applied at 18 g ai ha−1 provided the most effective hairy vetch control (> 90%) at both application timings among ALS inhibitors. Spring applications of several herbicides provided moderate (> 80%) to high (> 90%) levels of hairy vetch control, including: 2,4-D amine (140 g ae ha−1), mesosulfuron-methyl (15 g ai ha−1), tribenuron-methyl (13 g ai ha−1), and thifensulfuron/tribenuron-methyl treatments (16 and 32 g ai ha−1). Winter wheat injury was evaluated, but symptoms were negligible for most treatments. Winter wheat yields declined with increasing hairy vetch biomass. Fall herbicides may be prioritized to reduce hairy vetch competition during the fall and early spring growing season. Our research has established that several synthetic auxin and ALS-inhibiting herbicides, applied POST in fall or spring, can be safely used in winter wheat to control hairy vetch in an integrated weed management program.

Download Full-text

Acetolactate Synthase Inhibitor–Resistant False Cleavers (Galium spurium) in Western Canada

Weed Technology ◽

10.1614/wt-d-11-00075.1 ◽

2012 ◽

Vol 26 (1) ◽

pp. 151-155 ◽

Cited By ~ 11

Author(s):

Hugh J. Beckie ◽

Suzanne I. Warwick ◽

Connie A. Sauder ◽

Gina M. Kelln ◽

Chris Lozinski

Keyword(s):

Point Mutations ◽

Low Frequency ◽

Acetolactate Synthase ◽

Western Canada ◽

Resistance Factors ◽

Als Inhibitors ◽

Synthase Inhibitor ◽

Inhibitor Resistance ◽

Als Inhibitor ◽

Galium Spurium

Cleavers species (false cleavers and catchweed bedstraw) are among the top 10 most abundant weeds across the prairie region of western Canada, and are increasing in relative abundance at the fastest rate since the 1970s. In 2008, two false cleavers populations from Tisdale and Choiceland, Saskatchewan, were suspected of acetolactate synthase (ALS) –inhibitor resistance. Dose-response experiments were conducted with the use of imazethapyr and florasulam, both ALS inhibitors, as well as fluroxypyr, a synthetic auxin. Additionally, a 1,954–base-pair region of theALSgene including sites known to conferALSresistance were sequenced. Both populations were highly resistant to imazethapyr (resistance factors greater than 100), one population (Tisdale) was highly resistant to florasulam (Choiceland population susceptible, although a second, larger screening of 200 individuals indicated low frequency [2%] florasulam resistance), and both populations were susceptible to fluroxypyr. All sequenced Tisdale individuals screened with imazethapyr posessed the Trp574Leu mutation. In contrast, three point mutations were found for Choiceland individuals sequenced: Ser653Asn, Trp574Leu, and Asp376Glu. TheseALStarget-site mutations have not been documented previously in this species.

Download Full-text

Resistance to post-emergent herbicides is becoming common for grass weeds on New Zealand wheat and barley farms

PLoS ONE ◽

10.1371/journal.pone.0258685 ◽

2021 ◽

Vol 16 (10) ◽

pp. e0258685

Author(s):

Christopher E. Buddenhagen ◽

Trevor K. James ◽

Zachary Ngow ◽

Deborah L. Hackell ◽

M. Phil Rolston ◽

...

Keyword(s):

New Zealand ◽

Ad Hoc ◽

Acetolactate Synthase ◽

Stellaria Media ◽

Herbicide Resistant ◽

The North ◽

Mother Plants ◽

Als Inhibitors ◽

Als Inhibitor ◽

North And South

To estimate the prevalence of herbicide-resistant weeds, 87 wheat and barley farms were randomly surveyed in the Canterbury region of New Zealand. Over 600 weed seed samples from up to 10 mother plants per taxon depending on abundance, were collected immediately prior to harvest (two fields per farm). Some samples provided by agronomists were tested on an ad-hoc basis. Over 40,000 seedlings were grown to the 2–4 leaf stage in glasshouse conditions and sprayed with high priority herbicides for grasses from the three modes-of-action acetyl-CoA carboxylase (ACCase)-inhibitors haloxyfop, fenoxaprop, clodinafop, pinoxaden, clethodim, acetolactate synthase (ALS)-inhibitors iodosulfuron, pyroxsulam, nicosulfuron, and the 5-enolpyruvyl shikimate 3-phosphate synthase (EPSPS)-inhibitor glyphosate. The highest manufacturer recommended label rates were applied for the products registered for use in New Zealand, often higher than the discriminatory rates used in studies elsewhere. Published studies of resistance were rare in New Zealand but we found weeds survived herbicide applications on 42 of the 87 (48%) randomly surveyed farms, while susceptible reference populations died. Resistance was found for ALS-inhibitors on 35 farms (40%) and to ACCase-inhibitors on 20 (23%) farms. The number of farms with resistant weeds (denominator is 87 farms) are reported for ACCase-inhibitors, ALS-inhibitors, and glyphosate respectively as: Avena fatua (9%, 1%, 0% of farms), Bromus catharticus (0%, 2%, 0%), Lolium spp. (17%, 28%, 0%), Phalaris minor (1%, 6%, 0%), and Vulpia bromoides (0%, not tested, 0%). Not all farms had the weeds present, five had no obvious weeds prior to harvest. This survey revealed New Zealand’s first documented cases of resistance in P. minor (fenoxaprop, clodinafop, iodosulfuron) and B. catharticus (pyroxsulam). Twelve of the 87 randomly sampled farms (14%) had ALS-inhibitor chlorsulfuron-resistant sow thistles, mostly Sonchus asper but also S. oleraceus. Resistance was confirmed in industry-supplied samples of the grasses Digitaria sanguinalis (nicosulfuron, two maize farms), P. minor (iodosulfuron, one farm), and Lolium spp. (cases included glyphosate, haloxyfop, pinoxaden, iodosulfuron, and pyroxsulam, 9 farms). Industry also supplied Stellaria media samples that were resistant to chlorsulfuron and flumetsulam (ALS-inhibitors) sourced from clover and ryegrass fields from the North and South Island.

Download Full-text

The occurrence of herbicide-resistant Avena fatua (wild oats) populations to ACCase-inhibiting herbicides in Ireland

Irish Journal of Agricultural and Food Research ◽

10.15212/ijafr-2020-0127 ◽

2021 ◽

Author(s):

R. Byrne ◽

A.V. Vijaya Bhaskar ◽

J. Spink ◽

R. Freckleton ◽

P. Neve ◽

...

Keyword(s):

Herbicide Resistance ◽

Weed Management ◽

Resistance Mechanism ◽

Point Mutations ◽

Acetolactate Synthase ◽

Avena Fatua ◽

Integrated Weed Management ◽

Cross Resistance ◽

Wild Oats ◽

Als Inhibitor

Following growers’ reports of herbicide control problems, populations of 30 wild oats, Avena fatua, were collected from the south-east main arable counties of Ireland in 2016 and investigated for the occurrence and potential for herbicide resistance to acetyl-CoA carboxylase (ACCase) inhibitors pinoxaden, propaquizafop and cycloxydim, as well as acetolactate synthase (ALS) inhibitor mesosulfuron + iodosulfuron. Plant survival ≥20% was considered as the discriminating threshold between resistant and susceptible populations, when plants were treated with full recommended field rates of ACCase/ALS inhibitors. Glasshouse sensitivity screens revealed 2 out of 30 populations were cross-resistant to all three ACCase inhibitors. While three populations were cross-resistant to both pinoxaden and propaquizafop, and additionally, two populations were resistant to propaquizafop only. Different degree of resistance and cross-resistance between resistant populations suggest the involvement of either different point mutations or more than one resistance mechanism. Nevertheless, all populations including the seven ACCase-resistant populations were equally susceptible to ALS inhibitor. An integrated weed management (cultural/non-chemical control tactics and judicious use of herbicides) approach is strongly recommended to minimize the risk of herbicide resistance evolution.

Download Full-text

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

Weed Technology ◽

10.1017/wet.2020.23 ◽

2020 ◽

Vol 34 (5) ◽

pp. 652-660 ◽

Cited By ~ 1

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.

Download Full-text