Yellow Starthistle
(Centaurea solstitialis L.)
Sunflower family - Asteraceae

Photo from Weeds of the West, revised edition.

Photos from Montana Weed Control Association

Toxic: To Horses

Growth Habit: Annual, erect, rigid brancing stems.

Leaves: Basal leaves deeply lobed, upper leaves not lobed, small, sharply pointed.

Stem: Rigid, covered with a cottony fiber, to 30" tall, winged structures.

Flower: Yellow, terminal, flower bracts are tipped with straw-colored, 3/4 inch thorn.

Roots: Taproot.

Seeds: Smooth, light-colored, often darker mottled, 1/8 inch long, notched just above base.

Reproduction: Seeds.

Habitat: Rangelands, pastures, vineyards, abandoned croplands, alfalfa and small grain fields and roadsides.

Biological Controls: Seed head fly (Terellia uncinata).

Herbicides: None used in Yellowstone County at this time.

Produced by Wyoming Weed & Pest Council in cooperation with Sandoz Crop Protection Corp.