Yellow starthistle (Centaurea solstitialis) is one of the most widespread invasive broadleaf weeds on rangeland and natural areas in the United States infesting more than 14 million acres in the U.S.
It is a taprooted, winter annual, or rarely a biennial or short-lived perennial plant, that spreads by seed. Individual plants can produce more than 100,000 seeds, and dense infestations can yield 50 to 100 million seeds per acre. Plants produce one to many solitary, spiny, yellow flower heads beginning in late June and continuing through September and sometimes much later. Yellow starthistle displaces desirable vegetation in part through competition for available soil moisture. The weed is toxic to horses, and its spiny flower heads can reduce livestock carrying capacity.
Yellow starthistle can reduce habit and forage for wildlife, impact native plant and animal diversity, decrease land value, and reduce rangeland carrying capacity and groundwater resources. Yellow starthistle is also toxic to horses and causes and neurological disorder of the brain called ‘chewing disease’.
The weed is listed as noxious in at least 12 states in the U.S. and 2 Canadian provinces