BACKGROUND: Native to Eurasia, diffuse knapweed inhabits dry rangeland, roadsides, field edges, and waste areas. Knapweeds release chemical substances into the soil that inhibit the growth of competing vegetation.

DESCRIPTION: It is an annual or a short-lived perennial averaging 1 to 2 feet tall. Leaves have finely divided lobes. Flowers are white to rose in color. Diffuse knapweed differs from squarrose knapweed in that the terminal spine of the toothed flower bracts is straight rather than arched outward. It blooms throughout summer.

CONTROL: Several biocontrol agents are available and provide fair to good control. Select herbicides can offer good to excellent control when applied from rosette to pre-bud stages. Tillage offers good control.