Yellow star thistle (Centaurea solstitialis) is an annual weed found predominately in the western United States. C. solstitialis is a grayish-green colored plant which has multiple rigid stems extending in all directions from its base. It produces bright, star-like yellow flowers that are shielded by long, spiny bracts. C. solstitialis has a deep taproot, which allows it to thrive during dry, hot summers and drought periods. C. solstitialis begins to experience significant early growth in late May to early June and flowers early to mid-July. It can often can go unnoticed until the plant begins to flower, but once the bright yellow, dandelion like flowers bloom, the plant is easily detected.
The toxins present in C. solstitialis are eight sesquiterpene lactones that consist of: solstitialin A, repin, subluteolide, acroptilin, janerin, cynaropicrin, lactones solstitiolide and episolstitiolide.
- behavioral changes
MECHANICAL: Mow at early flowering.
BIOLOGICAL: Three seed head weevils, two seed head flies, yellow thistle bud weevil. Graze after bolting prior to spine formation. Several years needed to deplete seed reservoir.
CHEMICAL: Early spring herbicide application encourages grass competition.