Chlorsulfuron, metsulfuron, clopyralid, 2,4-D, picloram, and dicamba plus 2,4-D were spring-applied to musk thistle in rosette, bolting, bud, and early flower growth stages. All treatments reduced viable achene production at all musk thistle growth stages at Mcgrew, NE, and Longmont, CO. However, differences occurred at Evergreen, CO, among treatments and growth stages. No achenes developed at Evergreen when herbicides were applied during the rosette stage with dicamba plus 2,4-D, picloram, or metsulfuron at 21 g ai/ha or during bolting with chlorsulfuron or metsulfuron at 21 g/ha. Chlorsulfuron applied during early bloom reduced viable achene production over 99% compared to untreated plants and the picloram treatment.