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Widespread Occurrence of Herbicide-Resistant Italian Ryegrass (Lolium multiflorum) in Northern Idaho and Eastern Washington

  • Traci A. Rauch (a1), Donald C. Thill (a1), Seth A. Gersdorf (a1) and William J. Price (a2)


Persistent use of herbicides has resulted in the selection of many herbicide-resistant weeds worldwide. A survey of 75 fields in the Palouse region of the inland Pacific Northwest was conducted to determine the extent of Italian ryegrass resistance to grass herbicides commonly used in winter wheat-cropping systems. Plants grown from collected seed samples were tested for resistance to diclofop, clodinafop, quizalofop, tralkoxydim, sethoxydim, clethodim, pinoxaden, triasulfuron, mesosulfuron, flucarbazone, imazamox, and flufenacet/metribuzin. Averaged across herbicide families within a herbicide group, some level of resistance was exhibited in 73, 31, and 31% of the populations to the aryloxyphenoxypropionates, cyclohexanediones, and phenylpyrazoline herbicides, respectively, and 39, 53, and 55% of the populations to the sulfonylureas, sulfonylaminocarbonyltriazolinone, and imidazolinone herbicides, respectively. Twelve percent of the populations showed some level of resistance to flufenacet/metribuzin. Cross-resistance to all acetyl coenzyme A carboxylase-inhibiting (group 1) herbicides was observed in 12% of the populations, whereas 25% of the populations were cross-resistant to all acetolactate synthase-inhibiting (group 2) herbicides tested. Of all the populations tested, 7% exhibited multiple resistance to at least one herbicide within all three groups tested. Only 5% of populations were completely susceptible to all 12 herbicides tested. These results indicate that herbicide-resistant Italian ryegrass populations are now common across much of the Palouse region in northern Idaho and eastern Washington.

El uso persistente de herbicidas ha originado la selección de muchas malezas resistentes a ellos a nivel mundial. Una encuesta de 75 parcelas en la región Palouse en el interior del Pacífico Noroeste, EE UU., se llevó al cabo para determinar el grado de resistencia de la Lolium multiflorum L. LOLMU a herbicidas para zacates comúnmente utilizados en sistemas de cultivo de Triticum aestivum L. Se probaron plantas provenientes de muestras de diferentes semillas recolectadas por su resistencia al diclofop, clodinafop, quizalofop, tralkoxydim, sethoxydim, clethodim, pinoxaden, triasulfuron, mesosulfuron, flucarbazone, imazamox, y flufenacet/metribuzin. Promediando entre familias de herbicidas dentro de un grupo de dichos químicos se detectó algún nivel de resistencia en 73, 31, y 31% de las poblaciones a los herbicidas con aryloxyphenoxypropionates, cyclohexanediones, y phenylpyrazoline, respectivamente, y 39, 53, y 55% de las poblaciones al sulfonylureas, sulfonylaminocarbonyltriazolinone, e imidazolinone, respectivamente. El doce por ciento de las poblaciones mostró algún nivel de resistencia al flufenacet/metribuzin. Se observó resistencia cruzada a todos los herbicidas acetílicos CoA inhibidores de carboxylase (grupo 1) en el 12% de las poblaciones, mientras que el 25% exhibió resistencia cruzada a todos los herbicidas inhibidores de acetolactate synthase (grupo 2). De todas las poblaciones estudiadas, 7% mostró múltiple resistencia a cuando menos un herbicida de todos los tres grupos estudiados. Solamente el 5% de las poblaciones fue completamente susceptible a todos los doce herbicidas estudiados. Estos resultados indican que las poblaciones de Lolium multiflorum L. LOLMU resistentes a los herbicidas son actualmente comunes a lo largo de la mayor parte de la región Palouse en el norte de Idaho y el este de Washington.


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