Canada thistle (Cirsium arvense) is a colony-forming, exotic perennial found throughout much of the United States and Canada. Listed as a noxious weed in 43 states and 6 Canadian provinces, Canada thistle is one of the most important weeds in North America. The species has been shown to have negative impacts on crops, grazing and forage lands, and the larger biological community, including threatened and endangered species. Biological control of Canada thistle is being investigated as a control mechanism. In our work we evaluated the potential for combining stem-boring weevil (Hadroplotus litura) herbivory with competition from native bunchgrasses (Hesperostipa comata and Sporobolus airoides). We report on several combinations of treatments, some of which significantly reduce Canada thistle root biomass. These results suggest that integration of insect biocontrol with grass competition may be a useful approach for reducing Canada thistle infestations for a variety of purposes.