Noxious Weeds of Nebraska

Spotted knapweed (Centaurea maculosa Lam. = C. biebersteinii DC.) and diffuse knapweed (C. diffusa Lam.) are two of Nebraska's seven noxious weeds. These are closely related species that are well adapted to a variety of habitats including open forests, rangelands and pastures, Conservation REserve Program lands, roadsides, and ditch banks.

The knapweeds can establish in most soil types but are most productive in sandy, well-drained soils and thrive in dry environments. They typically invade disturbed sites along roads initially and subsequently spread into disturbed (especially overgrazed) rangelands and pastures. Diffuse and spotted knapweed leaves and shoots produce an allelopathic compound that reduces germination of common range grasses. Once established, both weeds have the capability to form pure stands that have little forage value.

Control measures include cultural, mechanical, chemical and biological.