Typically plants flower from late spring through summer and seed is produced in late summer. Because most of the large, heavy seed falls near the parent plant, stands can be extremely dense, smothering all other vegetation. Seed can also be disbursed by wind, water, animals, vehicles, and contaminated feed. Although most seeds germinate within the first 2 years, under the right conditions seed can survive up to 8 years. When soil is disturbed by road grading, cultivation or livestock concentration, buried seed can surface and germinate.
Distaff thistle grows in deep fertile soils and on poor, rocky hillsides.
Since distaff thistle reproduces from seed, control should focus on minimizing seed production. The two control methods for distaff thistle are chemical and mechanical. Because it is so closely related to safflower, biological control agents have not been introduced for fear of damage to commercial safflower crops. Successful control or eradication of distaff thistle requires following a strategy that integrates appropriate control methods with the life cycle and ecology of this plant. In developing a weed management strategy, consider the level of control that is reasonable to expect.