Centaurea diffusa (diffuse knapweed)

Centaurea diffusa

Photo courtesy Joseph DiTomaso

Centaurea diffusa (diffuse knapweed) is usually a biennial plant (family Asteraceae) that forms dense infestations. Seeds disperse when stems break off and tumble in the wind. Diffuse knapweed is not very common in California, but is one of the most invasive species in many other western states.

Cal-IPC Inventory rating: Moderate

Cal-IPC Resources on Centaurea diffusa

• California Invasive Plant Inventory Plant Assessment Form - Information gathered by Cal-IPC on the impacts, rate of spread, and distribution of invasive plants in California. Does not include management information.
• CalWeedMapper - Statewide maps, climate models, and reports.
• Cal-IPC News - Articles from our quarterly newsletter. Each issue is available as a pdf. List of articles on Centaurea diffusa.
• Cal-IPC Symposium Proceedings - Presentations and papers from our annual Symposium. List of articles on Centaurea diffusa.

Cal-IPC News Articles

• Donaldson, S. (2003). Fighting weeds in the Tahoe basin. CalEPPC News. 11: 7.
• Ogden, J. E., M. Renz, et al. (2007). "Dip-and clip": A new treatment for herbaceous weeds. Cal-IPC News. 14: 7.
• Pitcairn, M. (2000). All weeds that have approved biological control agents, accidental introductions and others. CalEPPC News. 8.
• Richardson, B. (2004). The A-rated north. Cal-IPC News. 12: 4-5,14.

Cal-IPC Symposium Proceedings

• Erskine-Ogden, J., M. J. Renz, et al. (2007). Managing herbaceous perennials in the Tahoe Basin. California Invasive Plant Council Symposium 2007. San Diego CA, California Invasive Plant Council.
• Butler, E. and S. Britting (1998). Mapping and control of weeds in the American River Parkway. California Exotic Pest Plant Council Symposium '98. Ontario, CA.
• Brucker, P. (2002). Salmon River cooperative noxious weed program. California Exotic Pest Plant Council Symposium 2002. Sacramento, California, CA.
• Brucker, P. (2003). Salmon River cooperative noxious weed program for 2003. California Invasive Plant Council Symposium 2003. Kings Beach, CA.
• Carrithers, V., B. Miller, et al. (2005). Aminopyralid: A new reduced risk active ingredient for control of broadleaf invasive and noxious weeds. California Invasive Plant Council Symposium 2005. Chico, CA.
• DiTomaso, J. M. (1995). Overview of extension non-crop weed research in California. California Exotic Pest Plant Council Symposium '95. J. Lovich, J. Randall and M. Kelly. Pacific Grove, CA.
• DiTomaso, J. M., C. Benefield, et al. (1998). Reproductive biology of yellow starthistle (Centaurea solstitialis) maximizing late season control. California Exotic Pest Plant Council Symposium '98. Ontario, CA.
• DiTomaso, J. M., G. B. Kyser, et al. (1998). Prescribed burning for control of yellow starthistle (Centaurea solstitialis) and enhanced native plant diversity. California Exotic Pest Plant Council Symposium '98. Ontario, CA.
• Donaldson, S., W. West, et al. (2003). Getting the job done: Working within the regulatory environment at Lake Tahoe to manage weeds. California Invasive Plant Council Symposium 2003. Kings Beach, CA.
• O'Connell, R. A. (1997). Hydrilla: A case study: The state of California's noxious weed eradication programs. California Exotic Pest Plant Council Symposium '97. Concord, CA.
• O'Connell, R. A. (1999). The state of California's noxious weed eradication programs. California Exotic Pest Plant Council. Sacramento, CA.
• Paris, R. B. and S. Erwin (2003). Diffuse Knapweed (Centaurea diffusa) vontrol on South Fork Mountain, Trinity County, California. California Invasive Plant Council Symposium 2003. Kings Beach, CA.
• Pitcairn, M. (1993). Introduction and distribution of biological control agents against exotic weeds in California. California Exotic Pest Plant Symposium '93. Westlake Village, CA.
• Rusmore, J. T. (1995). Use of fire and cutting to control yellow starthistle. California Exotic Pest Plant Council Symposium '95. M. Kelly and J. Lovich. Pacific Grove, CA.
• Smith, R. L., V. F. Carrithers, et al. (2006). Managing rangeland invasive plants with Aminopyralid (MilestoneTM). Cal-IPC Symposium. Rohnert Park, CA.
• Westbrooks, R. G. (1995). Federal regulatory efforts to minimize the introduction and impacts of exotic pest plants in the United States. CalEPPC Symposium '95. Asilomar, CA.
• Young, J. A., C. D. Clements, et al. (2000). Purple starthistle seed germination. California Exotic Pest Plant Council Symposium 2000. M. Kelly. Ontario, CA.

Other Resources on Centaurea diffusa

• USDA PLANTS database - Federal database with information on identification and distribution, and links to websites in individual states.
• Jepson Online Interchange for California Flora - Information on taxonomy, biology, and distribution from the UC Berkeley Jepson Herbarium.
• CalFlora - Distribution information by county based on submitted observations and herbarium specimens.
• The Nature Conservancy Management Summary - Information compiled by TNC land managers. Photos included for some species.
• Encycloweedia - Plants rated as noxious weeds by the California Department of Food and Agriculture.
• CalPhotos - Images of plants taken mostly in California.

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