Current state of herbicide resistance in Canada

Abstract

Biotypes of wild oat (Avena fatua L.) resistant to Group 1 herbicides in the prairie provinces, and biotypes of chickweed [Stellaria media (L.) Vill.] and kochia [Kochia scoparia (L.) Schrad.] in western Canada and pigweed (Amaranthus) species in Ontario resistant to Group 2 herbicides are most abundant and widespread. Evolution of resistance in these biotypes is attributable to frequent use of herbicides from these two respective groups. Increasing incidence of wild oat populations with multiple-group resistance will threaten the future effectiveness of herbicides of different modes of action. Proactive or reactive management for herbicide resistance in weeds must consider the risks of herbicides of different modes of action to select for resistance and the differing propensity of herbicides to be metabolized in herbicide-resistant biotypes when rotating among herbicides, must meet criteria for effective herbicide mixtures, and should incorporate agronomic practices in cropping systems that help reduce weed seed production and spread.