Musk thistle is a biennial weed that reproduces only from seed. The key to successful musk thistle control is to prevent seed production. Apply herbicides such as Tordon, Milestone, Transline, Vanquish/Clarity or 2,4-D to musk thistle rosettes in spring or fall. Apply Escort or Telar up to the early flower growth stage. Combine control methods into a management system for best results. usk thistle is an aggressive weed of foreign origin that occurs in pastures, rangeland, roadsides and non-crop area. It is a biennial weed, although occasionally it is an annual. Because musk thistle reproduces solely from seed, the key for successful management is to prevent seed production.