Diffuse Knapweed Diffuse Knapweed is a biennial single-stemmed plant with numerous lateral branches.
Flowers are white to rose, or occasionally purplish.
The flowerheads are slender with pointed, fringed bracts. Diffuse Knapweed will form dense stands on any open ground, excluding more desirable forage species. Once established, the necessary estensive control measures are often more expensive than the potential income of the land. Test plots by the OSU Extension Service have shown that residual chemicals are preferable when trying to control the weed. Always read and follow the label.