Thus, more seeds germinate and establish plants in open pastures and other degraded areas. Vigorously growing grass competes with musk thistle, and fewer thistles occur in pastures where grazing is deferred. However, musk thistle also can become a problem in pasture or rangeland that is in good condition. L. Phenology Seedlings normally emerge early in spring, develop into rosettes and spend the first season in this growth stage. Seedling emergence also can occur in fall.
All seedlings grow into rosettes and overwinter in that stage.
Early in spring of the second year, overwintered rosettes resume growth. 45 to 55 days after it bolts. Musk thistle dies after it sets seed. It spends approximately 90 percent of its life cycle in a vegetative growth stage. Musk thistle's tolerance to most herbicides increases after it bolts.