Ecology and management of diffuse knapweed (Centaurea diffusa Lam.)

Abstract

A close relative of spotted knapweed in the Asteraceae taxonomic family, diffuse knapweed is typically biennial, reproducing exclusively by seed. It forms a rosette with a central crown and tap root in the juvenile stage and a single upright stem one to three feet (0.3 to 0.9 m) tall with numerous spreading branches at maturity. White (occasionally purple) flowers are borne in heads with spiny bracts (see Figure 1). It is generally found on more arid sites than spotted knapweed. Native to the Mediterranean region, diffuse knapweed was first recorded in Montana from Mineral County in 1951 and by 2008 had been reported from 39 of Montana's 56 counties. Its dense, spiny overstory reduces the availability of desirable forage plants to livestock and wildlife, and grass production can be reduced by over 90% in heavy infestations.

Citation

Jacobs, Jim; Sing, Sharlene. 2008. Ecology and management of diffuse knapweed (Centaurea diffusa Lam.). Invasive Species Technical Note No. MT-20. Bozeman, MT: U.S. Department of Agriculture, Natural Resources Conservation Service. 12 p.