Centaurea diffusa

Centaurea diffusa_diffuse knapweed_flowerheads_JM DiTomaso
Photo courtesy Joseph DiTomaso

Synonyms: Acosta diffusa (Lam.) Sojak

Common names: diffuse knapweed

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 Rating: Moderate

Cal-IPC Assessment

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.

Weed RIC Management Notes

  • Management Notes - Information on management techniques and effectiveness from the University of California Cooperative Extension’s Weed Research & Information Center.

Cal-IPC Newsletter Articles

Cal-IPC Symposium Presentations

  • 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 Centaurea diffusa Information

  • CalPhotos - Images of plants taken mostly in California.
  • Calflora - See the distribution of this species on Calflora's map of California.
  • CalWeedMapper - Distribution information with ability to determine regional priorities.
  • Jepson Online Interchange for California Flora - Information on taxonomy, biology, and distribution from UC Berkeley's Jepson Herbarium.
  • CDFA - California official noxious weeds.
  • USDA PLANTS Database - Federal database with information on identification and distribution, and links to websites in individual states.
  • Bugwood - National database from the Center for Invasive Species and Ecosystem Health at the University of Georgia.