State Noxious Weed List -Yes

Growth form: Yellow starthistle is an annual which often grows 3 feet or more tall and is branched with winged stems. Each stem ends with a bright yellow flower that has needle-like straw colored bracts (spines) often up to 2 inches long. Lower leaves are deeply lobed while upper leaves are entire. Both stems and leaves have a gray pubescence. Yellow starthistle reproduces only by seed.

Yellow starthistle is a member of the knapweed family and spreads extremely rapidly. Seeds can germinate either in the fall and overwinter as a rosette or in the spring after snowmelt.

Livestock and wildlife will not graze where yellow starthistle grows because of the sharp spines around the flower. Yellow starthistle can cause “chewing disease” in horses, which is a lethal neurological disorder.