In Arkansas, thistles behave as biennials or winter annuals. Stem elongation begins in the spring, flowering begins in mid-April, seedheads start in May, and the plants die after the seedheads are mature.
Proper timing is essential to for good control.
Thistles should be in the rosette stage and actively growing with 60 degrees F. daytime temperatures at the time of herbicide application. The cheapest, 2,4-D, is very effective when applied at the correct rate and time. Spot treatment is a practical way to treat light or scattered infestations of thistles. Follow all directions on label.