Yellow Starthistle
Scientific Name: Centaurea solstitialis

History/Origin
          Yellow starthistle comes from the Mediterranean region of Europe. It is believed to have been first introduced into America with alfalfa seed transported to California late in the 1800's.

Biology/Ecology
           Although a thistle by name, it is really a member of the knapweed complex. This multi-branched plant is highly competitive and can often dominate a site. It is typically found in open areas associated with annual grasses.

           A single plant has the potential to produce up to 150,000 seeds, depending on surrounding plant densities and other environmental conditions. Of the produced seeds, 10% can stay dormant for more than10 years, 90% are viable, and about 60% of the seeds survive and produce seedlings. Two types of seeds are produced, those with parachute- like plumes (transported by wind) and those without (fall or travel with the seed head). Most seed germinate in the fall, but some can germinate during windows of opportunity throughout the year.

          Most plants form rosettes from March to May and then send up flowering stalks, tipped with bright yellow flowers. Their competitive ability is due to their rapid growth and nutrient uptake. They have little stress tolerance during this time and can easily die if their light, water, nutrients, or space requirements are not met. In the fall, the plants lose their leaves and leave a standing silver-grey skeleton with cottony-white seed heads. Seeds are dispersed by birds, humans, animals, whirlwinds, and vehicle transport.

Known Impacts
Detrimental:
          Yellow starthistle completely changes the natural habitat it invades. It crowds out native plant populations, reduces the number of plant species found in the area, and accelerates soil erosion. Thick stands reduce forage production. The large spines can cause serious damage to animal mouths and eyes. If starthistle is eaten by horses, it causes "Chewing Disease," a fatal neurological disorder.

Beneficial:
          The flowers provide nectar for honeybees and the mature seeds are a good source of food for ring-necked pheasant, California quail, house finches, and American finches.

Potential Locations
          Starthistle can be found on rangelands, roadsides, pastures, and fields throughout the western U.S. Although starthistle does not compete well with sagebrush, it will invade disturbed sagebrush communities. It favors sites originally dominated by perennial grasses that have deep loamy soil, south-facing slopes, and an annual precipitation of 12-25 inches (Winter or Spring).

Control/Management
          Yellow starthistle must produce a whole new population from seed every year. Because of this, controlling seed production and dispersal is the best way to reduce populations. Some of the tools available are:
• A combination of herbicide application and a reseeding of perennial grasses has proven effective (example herbicides: Clarity, Transline, Curtail, Tordon 22K [look at herbicide label: free search]).
• Hand-pulling in sensitive or small areas. Plowing or mowing in larger areas.
• Grazing can be used to suppress young plants before their spines develop.
• Burning for 2-3 consecutive years has shown promise in some studies.