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Rare Herbicide Resistance to a Noxious Weed (08/31/17)

A journal report from the Canadian Journal of Plant Sciences has confirmed herbicide resistance to spotted knapweed, a prohibited noxious weed that is primarily controlled with auxinic herbicides.

Rare Herbicide Resistance to a Noxious Weed

A journal report from the Canadian Journal of Plant Sciences has confirmed herbicide resistance to spotted knapweed, a prohibited noxious weed that is primarily controlled with auxinic herbicides. Scientists in Alberta Canada found a population collected from a managed rangeland in East Kootenay, BC that was highly resistant to both clopyralid (Stinger) and picloram (Tordon), with resistance:susceptible (R/S) ratios of >25 600 and 28, respectively. This is the first report of resistance in spotted knapweed. The research found only minor resistance to aminopyralid and no resistance to 2,4-D.

Rich Zollinger

Extension Weed Specialist

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