Resistance to Aryloxyphenoxypropionate Herbicides in Two Wild Oat Species (Avena fatuaandAvena sterilisssp.ludoviciana)

Abstract

Resistance to the methyl ester of diclofop, an aryloxyphenoxypropionate graminicide, was shown for a wild oat (Avena fatua) population from Western Australia, and marked resistance to a range of aryloxyphenoxypropionate and cyclohexanedione graminicides was detected in a winter wild oat (Avena sterilisssp.ludoviciana) population from South Australia. TheA. sterilisbiotype exhibited high levels of resistance to the aryloxyphenoxypropionate herbicides diclofop, fluazifop, haloxyfop, fenoxaprop, quizalofop, propaquizafop, and quinfurop and low levels of resistance to the cyclohexanedione herbicides sethoxydim, tralkoxydim, and cycloxydim. Ratios of LD50values for responses of resistant and susceptibleA. sterilisto the aryloxyphenoxypropionate herbicides were between 20 for propaquizafop and > 1,000 for fluazifop, and were between 2.5 and 3 for the cyclohexanedione herbicides. The LD50value for diclofop for theA. fatuabiotype was 442 g ai ha-1which was 2.7-fold that of a susceptible control. Thirty-three percent of the plants survived at the registered rate of application.