Field and producer survey of ACCase resistant wild oat in Manitoba

Abstract

In a previous study, 729 townships in Manitoba were differentiated as being at low, medium, or high risk of evolving wild oat resistant to Group 1 herbicides based on herbicide use histories from 1981 to 1993. In the present study, 16 townships representing the three risk categories were surveyed in 1994 in order to determine the percentage of resistant wild oat patches. As well, a questionnaire was mailed to farmers in these townships requesting information on practices and attitudes relating to herbicide resistance. The wild oat survey consisted of sampling seed from conspicuous wild oat patches visible from north-south roads in each township. A total of 533 samples were collected and screened with fenoxaprop-P and sethoxydim using a bioassay. An average of eight resistant wild oat patches was found in the high risk townships. This was significantly higher than in low and medium risk townships where an average of less than one resistant wild oat patch per township was detected. The attitude of producers towards herbicide resistance was similar in all risk categories. However, the number of respondents suspecting Group 1 resistance on their farms was related to risk categories with producers in high risk areas suspecting the most cases of resistance. Key words: Weed survey, resistance assessment, wild oat, ACCase inhibitors