. 2015. Glyphosate and acetolactate synthase inhibitor resistant common ragweed (Ambrosia artemisiifolia L.) in southwestern Ontario. Can. J. Plant Sci. 95: 335Á338. Common ragweed (Ambrosia artemisiifolia L.) was found to be resistant to glyphosate in Ontario. Field surveys were conducted from 2011 to 2013 to determine the distribution of glyphosate-resistant (GR) and acetolactate synthase inhibitor resistant common ragweed. GR common ragweed was confirmed in Essex County. All GR populations were found to be resistant to acetolactate synthase-inhibiting herbicides.