Alturas Field Office

Noxious Weeds

 

Diffuse Knapweed   (Centaurea diffusa)
Sunflower Family (Asteraceae)

 

Diffuse Knapweed
Photo courtesy of the University of Idaho

 
 

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Description:  A slender, highly branched annual or short-lived perennial 1 to 2 feet. Stems rough to the touch. Leaves narrow, pinnately divided below, reduced above. Flowers numerous, narrow, with white to rose, but sometimes purplish, ray flowers. Phyllaries with marginal, comb-like bristles and a distinct slender spine on the tip. Seeds are brown or grayish, without bristles.

Habitat:  Native to southwest Europe. This weed grows on dry roadsides, waste areas, and rangelands. A highly competitive plant which replaces native and desirable vegetation.

Distribution:  The three largest infestations of diffuse knapweed found in northeastern California consist of 10 acres or more each. They are along McAdams Creek (Siskiyou County), south of New Pine Creek (Modoc County), and south of McCloud (Shasta County). Small populations and single plants can be found along many of northeastern California's roadways.

Flowering Period:  July to October.