A survey of 109 fields was conducted across western Canada in spring 2007 to determine the extent of ALS-inhibitor and dicamba (synthetic auxin) resistance in kochia. Weed seedlings were collected from fields in three provinces of western Canada and transplanted into the greenhouse. Seeds were harvested from selfed plants, and the F1 progeny were screened for resistance to the ALS-inhibitor mixture thifensulfuron–tribenuron or dicamba. All kochia populations were susceptible to dicamba. ALS inhibitor–resistant kochia was found in 85% of the fields surveyed in western Canada: 80 of 95 fields in Alberta, six of seven fields in Saskatchewan, and all seven fields in Manitoba. For the 93 ALS inhibitor–resistant populations, the mean frequency (±SE) of parental plants classified as resistant was 61 ± 3%. Most of the resistant populations (87%) were heterogeneous and contained both resistant and susceptible individuals. ALS sequence data (Pro197 and Asp376 mutations) and genotyping data (Trp574 mutation) obtained for 87 kochia parental (i.e., field-collected) plants confirmed the presence of all three target-site mutations as well as two mutational combinations (Pro197 Trp574, Asp376 Trp574) in resistant individuals.
Nomenclature: Dicamba; thifensulfuron; tribenuron; kochia, Kochia scoparia (L.) Schrad. KCHSC, synonym: Bassia scoparia (L.) A.J. Scott