(Centaurea maculosa Lam )
Life Span: Perennial
(Centaurea diffusa Lam )
Life Span: Biennial (or short-lived perennial)
The reason these plants are considered noxious is:
1. They are very aggressive, infesting dry rangeland and waste areas.
2. They are prolific seed producers.
3. They are highly competitive, even killing vegetation that grows below them.
These two plants have not been on the noxious weed list for very long, only since 1992. Both plants are very difficult to distinguish between each other in the rosette stage. Both plants behave and look almost alike, but they have different blossom bracts (under the flower), and the Spotted is usually purple, while the Diffuse is usually white.
For a more detailed description of Knapweeds, check out the Nebraska Weed Control Association Website.