Abstract:
Wild mustard (Sinapis arvensis L.) is a common and competitive weed of field and horticultural crops and occurs across all of the Canadian provinces. Since 1989, wild mustard has been effectively controlled in argentine canola (Brassica napus L.), polish canola (Brassica rapa L.) and commercial brown mustard (Brassica juncea L.) by ethametsulfuron-methyl. In 2000, splaying with ethametsulfuron failed to control 20 geographically separate wild mustard populations in conventional canola crops in southem Manitoba. Escaping patches of wild mustard were sampled in August of 2000 and ethametsulfuron herbicide resistance was confirmed at the whole plant level in a greenhouse trial. Subsamples of four acetolactate synthase (ALS) inhibitor resistant wild mustard populations (and a known susceptible population) were selected for indoor, whole-plant, dose response experiments to characterize the patterns and levels of cross-resistance to several ALS inhibitor herbicides and to the group 4 herbicide 2,4-D. ALS inhibitor herbicides used in these indoor dose-response experiments included ethametsulfuron, thifensulfuron, and imazethapyr. Furthermore, the insecticide malathion, which is a known inhibitor of Cytochrome P450 enzymes, was tank-mixed with ethametsulfuron in an additional dose-response experiment. In 2002, one ALS inhibitor resistant wild mustard population was evaluated in a separate field experiment to determine the efficacy of group 2 herbicides in competition with a competitive canola crop. The results of the greenhouse experiments show that that pattems of resistance to ethametsulfuron varied among biotypes with one biotype showing a very high level of resistance...
