First report: spotted knapweed (Centaurea stoebe) resistance to auxinic herbicides

By Amy R. Mangin and Linda M. Hall

Abstract: Spotted knapweed is a prohibited noxious weed that is primarily controlled with auxinic herbicides. A population collected from a managed rangeland in East Kootenay, BC, was highly resistant to both clopyralid and picloram, with R/S ratios of >25 600 and 28, respectively. This is the first report of resistance in spotted knapweed.

Key words: spotted knapweed, herbicide resistance, clopyralid, aminopyralid, 2,4-D, picloram.