Herbicide resistance in Canada: Biggest threats, best management,and lessons learnt

摘要

I began my career in weed science dealing with the first case of herbicide resistance in western Canada in 1988: trifluralin-resistant green foxtail (Setaria viridis (L.P.) Beauv.). Thirty years later, there are 76 herbicide-resistant (HR) weed biotypes across Canada. The biggest threats to crop production are multiple-resistant wild oat (Avena fatua L.) and kochia (Kochia scoparia L. Schrad.) in western Canada and Canada fleabane or horseweed (Conyza canadensis (L.) Cronq.) in eastern Canada. Management of glyphosate plus ALS inhibitor-resistant Canada fleabane in soybean requires tank-mixing three herbicide modes of action, with significantly increased cost. Alternatively, Roundup Ready (RR) 2 Xtend~(TM) (glyphosate + dicamba) soybean cultivars, introduced in 2017, were planted on 13% of crop area as a tool to control these populations. Glyphosate plus ALS inhibitor-resistant kochia in western Canada, similar to Canada fleabane, has spread very rapidly due to HR allele movement via seed and pollen, increasing reliance on auxinic herbicides. Many farmers cannot control wild oat post-emergence in wheat or barley due to resistance to both ACCase and ALS inhibitor herbicides, relying on pre-emergence tank-mixes. 1 outline best management practices recommended for HR weed management, such as crop diversity, crop competitiveness, and weed sanitation (including harvest weed seed control). Whereas near-monoculture RR soybean in eastern Canada has contributed to increasing occurrence of glyphosate-resistant weeds, genetically-engineered canola (Liberty Link~(TM) (LL) or RR trait) in western Canada has positively impacted HR weed management over the past 20 years. I will share some lessons on HR weed management I have learnt as a weed scientist and as afarmer over the past 30 years.