Bull Thistle

Cirsium vulgare

Family: Asteraceae

Weed class: C
Year Listed: 1988
Native to: Europe, Asia and Northern Africa
Is this Weed Toxic?:

not known to be

Why Is It a Noxious Weed?

Bull thistle may outcompete native plants and desirable wildlife and livestock forage plants. It can invade most any disturbed habitat and grow in dense thickets. Hay price may decline with the presence of bull thistle.

How would I identify it?

General Description

Bull thistle is a biennial herbaceous plant growing between 3 to 7 feet tall with one upright branched stem. It grows a rosette (cluster of radiating leaves at plant base) in its first year and blooms in its second year.

Flower Description

Flowerheads many, 1.5 to 2 inches in diameter. Bracts at base of flowerheads are spine-tipped. Flowers are purple or rarely white, blooming July through September.

Leaf description

Leaves alternate and coarsely lobed. Each lobe has a spined tip. Leaf bases extend downward from the leaves along prominent ridges of the stem. Upper leaf surface is rough with bristle-like spines while the undersides are covered with white woolly hairs.

Stem description

Stems are spiny-winged from leaf bases extending downward producing a winged ridge effect.

Fruit Seed Description

Seeds are less than 0.16 inches (4 mm) long.

Where does it grow?

Bull thistle colonizes primarily in disturbed areas such as pastures, roadsides, and ditch banks as well as in hayfields, disturbed prairies and logged mountain areas. Please click here to see a county level distribution map of bull thistle in Washington.

How Does it Reproduce?

Bull thistle reproduces by seed and not by vegetative means.

How Do I Control It?

Mechanical Control

Hand-pull and dispose of flowering plants in trash to prevent seed spread. Mowing can be effective, but make sure the plants do not flower. If cut too early before flowering, plants may re-sprout and flower again that season. Remove stems from site if plants are cut or pulled with flowers.

Biological Control

Bull thistle seed production is impacted by the seedhead gall fly, Urophora stylata. This gall fly’s larvae induce and feed on gall tissue in the developing bull thistle seedhead, reducing seed production up to 60%. Urophora stylata may significantly reduce seed production if bull thistle populations are sustained for many years. For more information about the biological control of bull thistle, please visit WSU Extension Integrated Weed Control Project