Mapping risk areas for resistance to ACCase inhibitor herbicides in Manitoba

Since 1976, seven acetyl coenzyme-A carboxylase (ACCase) inhibitors (referred to as Group 1 herbicides) have been registered in western Canada for wild oat (Avena fatua L.) and green foxtail (Setaria viridis L.) control. In 1990, Group 1 resistant wild oat populations were identified from fields in Manitoba which had been repeatedly sprayed with these products during the previous 10 yr. Since the occurrence of resistance is directly related to the frequency of herbicide use, the purpose of this study was to compile herbicide use histories on a province-wide basis using data included in the Manitoba Crop Insurance Corporation (MCIC) database. The database was used to determine the relative importance of Group 1 herbicide use in major crops compared with other products, and to identify individual townships at low, medium and high risk for developing Group 1 resistance. Low, medium and high risk townships were arbitrarily defined as those in which Group 1 products were used on less than 30%, on 30 to 50% and...