Typical plant growing in disturbed site.
Common thistle, spear thistle
Bull thistle grows as a rosette (ground‐hugging form) in the first year, and then sends up stems and flowers in the second year, growing to 6 feet tall.
Pink to purple, vase‐shaped and in branched clusters at the ends of the stems. Bracts (modified leaves located under the flower petals) are spiny. Blooms from summer to fall.
Lobed, hairy and rough on the upper side; soft on the underside, with a raised center vein. Leaves are rough when rubbed towards the base. Lobe tips have long, stiff spines. The lobe at the end of the leaf is elongated.
Hairy, spiny‐winged and branched.
Forms many stiff, brown burrs. This is the point at which most people notice the plant.
Eurasia; naturalized to much of the United States.
Rangeland, roadsides, edges of fields, burned areas and other disturbed or mismanaged sites.
Biennial (flowers and dies in the second year)
Reproduces by seed
Bull thistle is easiest to control in the rosette stage. Prevent seed production to avoid spread by blowing seeds. However, simply cutting off the blooms does not provide sufficient control, as the plant will produce more flowers.
Dig or pull plants, removing 2 inches of the top of the root. Mowing is not effective, as the weed can regrow from the roots and bloom close to the ground.
Plant desirable, thick stands of vegetation to compete with bull thistle. Tall grasses can help shade out the weed.
A seedhead‐feeding fly, Urophora stylata, is available for use in controlling large infestations.
Spot‐treat young plants with broadleaf‐selective herbicides. Use a surfactant to increase absorption of the herbicide by the fuzzy leaves.
All photos by S. Donaldson.
Colorado State Parks. 2005. Colorado State Parks Weed Profile: Bull Thistle.
DiTomaso, J.M. and E.A. Healy. 2007. Weeds of California and Other Western States. University of California Publication 3488.
Forest Health Staff. 2005. Bull Thistle. USDA Forest Service, invasive
Whitson, Tom D. (editor). 2002. Weeds of the West. University of Wyoming, Jackson, Wyoming.
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Donaldson, S. and Hanson Mazet, W., 2010, A Northern Nevada Homeowner’s Guide to Identifying and Managing Bull Thistle, Extension | University of Nevada, Reno, FS-10-19
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