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Herbicide resistance in the Canadian prairie provinces : Five years after the fact

2005; Volume: 75; Issue: 4 Linguagem: Inglês

10.7202/706067ar

1710-1603

I.N. Morrisson, M. D. Devine,

Pesticide and Herbicide Environmental Studies

Herbicide resistance was first recognized as a problem on the Canadian Prairies in 1988 when trifluralin-resistant green foxtail ( Setaria viridis ) was reported in Manitoba, and chlorsulfuron-resistant chickweed ( Stellaria media ) and koehia ( Kochia scoparia ) in Alberta and Saskatchewan, respectively. Since then, the number of resistant weeds has increased to include wild oats ( Avena fatua ) resistant to triallate and to aryloxyphenoxypropionate and cyclohexanedione (group 1) herbicides, green foxtail to group 1 herbicides, Russian thistle ( Salsola pestifer ) and wild mustard ( Sinapis arvensis ) to sulfonylurea and imidazolinone (group 2) herbicides, and wild mustard to growth regulator (group 4) herbicides. The levels and patterns of cross-resistance to chemicals in groups 1 and 2 vary widely among different populations, with resistance factors [resistant to susceptible (R:S) ratios] derived from dose response curves typically ranging from < 2 to > 150. Group 1 resistance in green foxtail and group 2 resistance in chickweed and kochia populations are due to reduced sensitivities of the target enzymes, acetyl coenzyme-A carboxylase (ACCase) and acetolactate synthase (ALS), respectively. The mechanisms of resistance in the other species including wild oats resistant to ACCase inhibitors (group 1 ) and to triallate/difenzoquat (group 8) are unclear. At present, the only instance of multiple resistance in western Canada is green foxtail resistant to chemicals in both groups 1 and 3 (ACCase inhibitors and dinitroanilines). Future concerns focus mainly on the increasing seriousness of group 1 and 8 resistance across the Prairies, and on the possibility of selecting for multiple resistance in weeds such as green foxtail for which there are few remaining effective control options.