BULL THISTLE (Cirsium vulgare)

Description: Bull thistle, also referred to as spear thistle, Fuller’s thistle and lance-leafed thistle, is a member of the Asteraceae or sunflower family. Bull thistle can grow 2 to 5 feet tall with numerous spreading branches. Stems of the plant are sparsely hairy, irregularly and spiny winged, green or brownish in color with purple veins. Leaf margins are double dentate (toothed and toothed again), each ending in a lone stiff spine. The leaf surface of the plant has a distinct center vein with slight pubescence on the topside and more underneath. Flower heads are usually solitary on the end of each stem, gumdrop-shaped, one to two inches tall with long, stiff, yellow tipped spines. Flowers are generally bright purple but sometimes white in color. Seeds are light-colored with dark brown to black longitudinal stripes. Seeds are generally 1/16 inch long, oblong, somewhat flattened or curved, with a long, white, hairy plume.

Plant Images:

Bull thistle

Rosette Leaf Gumdrop-shaped flower

Distribution and Habitat: This thistle is generally found in the northern and eastern counties in North Dakota and is the least serious of the introduced thistles in the s tate. The plant thrives in moist soils and is less common on sand and pure clay soils. Typical habitats include disturbed or degraded land, such as roadsides, fence rows, overgrazed pastures and rangelands, eroded gullies, ditch banks and vacant lots.

Life History/Ecology: Bull thistle is a biennial that reproduces and spreads solely by seed production. Germination of the plant occurs in the spring or during the fall in response to adequate soil moisture. During the first year, plants grow as a rosette and develop a fleshy taproot that does not creep like Canada thistle. Developing rosettes may grow slowly in winter or cease growth altogether during severe cold. By the second growing season, plants resume growth and bolt. Bull thistle flowers from July to September and may bear 10 to 200 flower heads per plant. Bull thistle averages 100 seeds per flower head, but may produce up to 350 under ideal environmental conditions. A healthy plant may produce 5,000 to 50,000 seeds.

History of Introduction: Bull thistle is native to Europe, western Asia and North Africa. The plant was introduced in western North America via overseas shipping through Portland, OR, in the late 1800s. Bull thistle was reported to be common in Arizona, California, Colorado, Nevada, Oregon, Utah, Washington and Wyoming by 1900. In North Dakota, scattered occurrences are known from eastern, central, northwestern, and southwestern parts of the state. Populations have been reported in Divide, Burke, Ward, McLean, Bottineau, Pembina, Grand Forks, Nelson, Cass, Barnes, LaMoure, Ransom, Richland, Sargent, Stark and Towner counties.

Effects of Invasion: Bull thistle is regarded as a noxious pest in protected areas and parks like Yosemite, Yellowstone, Grand Teton and Glacier National Parks. The plant reduces desirable plant species, interferes with livestock grazing and has no significant nutritive value. Bull thistle can dominate forests that have recently been clear-cut and become a problem in arable fields after establishment of alfalfa.

Control: Management objectives for bull thistle control include early detection and preventing seed production. Seeds of bull thistle can remain viable in the soil for one to five years, therefore infestations should be monitored to prevent re-establishment. Control methods conducted during the seedling or rosette growth stage of the plant have been the most effective. An integrated management system may include seeding desirable competitive grasses following other control methods to prevent the spread of bull thistle and improve the plant community to a more desirable, productive state.

Mechanical - Mechanical methods that sever the root below the soil surface will kill the weed because bull thistle does not reproduce from the root system. Repeated hand pulling, hoeing, tillage, and mowing have been used to control bull thistle. These methods should be done before the reproductive growth stages to prevent seed production and dispersion. A single mowing may not effectively control bull thistle if conducted shortly before flowering because some plants may resprout and produce seeds. Therefore, mowing should be conducted prior to seed dispersal and repeated since infestations generally consist of various growth stages. Tillage can be effective in reducing bull thistle, but may not be appropriate in wildlands and rangelands. In Yosemite National Park, less than 5 percent of adult bull thistle plants that were cut at the soil surface resprouted. Prescribed burning has had variable control on bull thistle. In a South Dakota tallgrass prairie site, prescribed burns conducted over a four to five year rotation during the late spring, reduced bull thistle infestations and increased desirable native species. In Oregon, bull thistle populations were enhanced following a burn. Further research is needed to determine the effective of prescribed burns for bull thistle control.

Chemical - Herbicides such as 2, 4-D, clopyralid, clopyralid plus triclopyr, picloram, dicamba and glyphosate will control the plant. Herbicides should be applied in late fall or early spring when thistles are in the seedling to rosette stage. Bull thistle only reproduces by seed; therefore, herbicides applied prior to flowering will eventually eradicate infestations. Herbicides such as metsulfuron and chlorsulfuron can be applied in the spring when the plant is in the bolting to bud growth stage.

Contact your local county extension agent for recommended use rates, locations and timing. Biological - No biological control agents are not recommended for bull thistle control in North Dakota at this time. A few biological control agents have been released on bull thistle but have also been found feeding on native thistles. A thistle head weevil, Rhinocyllus conicus, introduced to control musk thistle but has been observed on bull thistle as well. This weevil has been reported to reduce seed production in musk thistle but the results are unclear of the effect the agent has on bull thistle. A gall fly, Urophora stylata, feeds on developing seeds found within the flowerheads of bull thistle. One study found that seed production was reduced by 60 percent with the gall fly.

Livestock generally do not feed on bull thistle shoots after maturity due to the spines on the plant. Overgrazing can result in an increase of bull thistle.

References:

Beck, K. G. 1999. Biennial thistles. p. 145-161 In R. L. Sheley and J. K. Petroff. Biology and Management of Noxious Rangeland Weeds. Corvallis, OR: Oregon State University Press.

Coombs, E. M., Piper, G. L., Rees, N. E. 1996. Bull thistle: Cirsium vulgare. In: Rees, N. E., Quimby, P. C. Jr., Gary, L. [and others], eds. Biological control of weeds in the west. Bozeman, MT: Western Society of Weed Science. In cooperation with: U.S. Department of Agriculture, Agricultural Research Service; Montana Department of Agriculture; Montana State University: Section II.

Department of Natural Resources Trails and Waterways. 2003. Bull thistle (Cirsium vulgare) p. 39-40 In Minnesota invasive non-native terrestrial plants and identification guide for resource managers. MN Dept. Nat. Res., St. Paul, MN.

Forcella, F. and J. M. Randall. 1994. Biology of bull thistle, Cirsium vulgare (Savi) Tenore. Rev. Weed Sci. 6:29-50.

Klinkhamer, P. G. L. And T. J. de Jong. 1993. Cirsium vulgare (Savi) Ten. J. Ecol. 81(1):177-191.

Lym, R. G. and K. M. Christianson. 1996. The thistles of North Dakota. North Dakota State Univ. Ext. Ser. Circ. W-1120. Fargo, ND.

Mitich, L. W. 1998. Bull thistle, Cirsium vulgare. Weed Technol. 12:761-763.

Whitson, T. D., editor. 2000. Weeds of the West 9th Ed. Western Society of Weed Science, Newark, CA 94560. 630pp.

Zouhar, K. 2000. Cirsium vulgare. In: Fire effects information system [Online]. U. S. Department of Agriculture, Forest Service, Rocky Mountain Research Station, Fire Sciences Laboratory (Producer). Available at: http://www.fs.fed.us/database/feis/ (January 2005).

Mature bull thistle photograph courtesy of University of Nevada Cooperative Extension.

Rosette photograph courtesy of Stevens County Noxious Weed Control Board, Washington.

Leaf photograph courtesy of Dan Tenaglia, www.missouriplants.com and www.invasive.org.

Gum-drop shaped flower photograph courtesy of North Dakota State University, NDSU Extension Service.