Did you know?
Gophers can unintentionally "farm" bull thistle!
How did bull thistle get here?
Bull thistle is native to Europe, Asia, and Africa. It is now found on every continent except Antarctica. It is thought to have been introduced to eastern North America during colonial times and to western North America in the late 1800s and early 1900s. Bull thistle is now considered the most common rangeland thistle in western North America.
What are its characteristics?
Bull thistle is typically a biennial forb. In the juvenile phase, plants form a rosette with a taproot up to 28 inches long. Rosettes can grow to 3 feet in diameter. During the second year, stems grow 1 to 6 feet tall, often with many spreading branches. Bull thistle reproduces and spreads entirely from seeds. Plants produce about 100 to 300 seeds per flowerhead, and anywhere from 1 to over 400 flowerheads per plant. The majority of seeds fall close to the parent plant and dense patterns of seedlings radiate outward from the parent plant. Seed viability is generally high. Pocket gophers “farm” bull thistle by consuming taproots from below and their digging provides sites for further thistle establishment. The younger stems and roots of bull thistle are edible, and Native Americans used them for food. Anecdotally, it has been suggested that bull thistle may be processed to produce rubber.
Why is bull thistle a problem in the Great Basin?
Bull thistle is most troublesome in recently or repeatedly disturbed areas such as pastures, overgrazed rangelands, burned areas, and along roads, ditches, and fences. Bull thistle competes with desirable forage and has no significant value for livestock. Plants are usually avoided by grazing animals because of their spines. Bull thistle litter may inhibit the growth of other plants.
How can we fight this weed?
Introduced weevils are effective biological control agents, but rare native thistles are also affected. Chemical control is most effective when plants are in the rosette stage and least effective when thistles are flowering.
Refer to the Weed Management Handbook on the University of Wyoming Extension website for current herbicide information. Close mowing or cutting two times per season will usually prevent seed production. As with all restoration projects, more success is gained when desirable species are planted following removal of weeds.
-Drawing: USDA-NRCS PLANTS Database / Britton, N.L., and A. Brown. 1913. Illustrated flora of the northern states and Canada. Vol. 3: 549.
-Flower: Christopher L. Christie © 2005.
-Plant: Oregon State University Jed Colquhoun photo Collection.
-USDA, NRCS. 2006. The PLANTS Database (http://plants.usda.gov, 26 September 2006). National Plant Data Center, Baton Rouge, LA 70874-4490 USA.
-Whitson, T. D., et.al. 2000. Weeds of the West., 9th ed. Western Society of Weed Science, Newark, CA.
-Zouhar, Kris 2002. Cirsium vulgare. In: Fire Effects Information System, [Online]. U.S. Department of Agriculture, Forest Service, Rocky Mountain Research Station, Fire Sciences Laboratory (Producer). Available: (http://www.fs.fed.us/database/feis/, 26 September 2006).