Weeds - Yellow Starthistle
Yellow starthistle is usually a winter annual germinating in the fall but can also have early spring germinates. The plant has yellow flowers from an urn shaped seed head typical of the aster family, with long sharp stiff spines at the end of its bracts. Some seeds have parachute hairs and some don't, resulting in a distribution that produces dense stands and rapid spreading. The plant is toxic to horses causing chewing desease which is irreversible and always fatal.
Yellow starthistle is an aggressive, adaptable weed that inhibits the growth of desirable plants in pasture, rangelands and waste land. It can become a problem in CRP ground where the grass stand is weak. The plant has been found in wheat crops where waste lands are heavily infested.
Residual chemicals are preferred for control, due to the long germination period. Picloram (Tordon 22K), dicamba (Banvel), and 2,4-D LV and Amine are effective. Always read and follow the label. Biological controls may be available for sites with sufficient plant densities. Fortunately Malheur County has had limited outbreaks which have all been contained, however rapid response is esential.