Spotted knapweed. Salt cedar. Leafy spurge. Musk thistle. Dalmation toadflax.
BLM>Wyoming>Programs>Weeds & Pests>Species>Bull Thistle
Print Page

Bull Thistle


Bull Thistle.


Bull Thistle.

Interesting Facts

  • Can grow up to 7 feet tall
  • Dense infestations of this spiny plant can exclude livestock and wildlife movement
  • Seeds have a silky down covering allowing windblown dispersal of great distances


Bull thistle is a large spiny forb that can grow 7 feet in height

  • Stems have spiny wings and grow 1 to 7 feet tall, with many spreading branches, and sometimes a single stem
  • Leaves are more or less lance-shaped and 3 to 12 inches long, prickly hairy on the top and very hairy underneath
  • Flowers Bull thistle flower heads are 1.5 to 2 inches in diameter, 1 to 2 inches long, usually solitary, and more or less clustered at the ends of shoots and branches.
  • Seeds are 5 mm long, with a downy pappus


Bull thistle is a very widespread weed that can grow in a wide range of environments but is most troublesome in disturbed areas such as pastures, overgrazed rangelands, recently burned forests and forest clearcuts, and along roads, ditches, and fences. Bull thistle is found on dry and wet soils, but is most common on soils with intermediate moisture.

Ecological Impacts

Although bull thistle is a problem predominantly in disturbed areas, it also can be found in natural areas. The basal rosette may grow to nearly 3 ft. in diameter before bolting, and, once established, bull thistle out-competes native plant species for space, water, and nutrients.


  • Mechanical: Mowing with a brush type mower can be an effective method for control.
  • Chemical: It can be effectively controlled using any of several readily available general use herbicides such as glysophate or triclopyr.
  • Biological: The seed-feeding fly, Urophora stylata Fabricius, has been selected and released for biological control of bull thistle