BACKGROUND: Yellow starthistle was introduced from Europe. It grows well on dry sites in rangeland, roadsides, and waste areas. It can cause “Chewing disease” in horses that consume it.

DESCRIPTION: Yellow starthistle is a 2 to 3 foot tall winter annual with blue-green coloration. Rosette leaves are deeply lobed and could be confused with dandelion. Stems are winged and sparsely leaved. Flowers are yellow. Cream-colored thorns, ¼ to ¾ inch long, protrude from the flowering heads. Bloom is in early summer.

CONTROL: Several biocontrol agents have been tested, but availability is limited. Select herbicides offer fair to good control when applied between rosette and bloom stages. Tillage is effective.