There are currently 509 unique cases (species x site of action) of herbicide resistant weeds globally, with 266 species (153 dicots and 113 monocots). Weeds have evolved resistance to 21 of the 31 known herbicide sites of action and to 164 different herbicides. Herbicide resistant weeds have been reported in 95 crops in 71 countries. The website has 3083 registered users and 648 weed scientists have contributed new cases of herbicide resistant weeds. View Recent Additions, Site of Action Summary, or the Herbicide Classification System.