Cirsium arvense var. arvense and C. arvense var. horridum were subjected to different concentrations of amitrole and glyphosate, and the injury symptoms recorded. Equal rates of the 2 herbicides were of approximately equal efficacy in preventing regrowth of shoots from the root systems, although their visible effects on the shoots and roots of treated plants were very different. Glyphosate will provide an effective alternative to amitrole for control of C. arvense.