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The Mission of the Yellowstone County Weed Department is to assist the public, private, and other government agencies to manage and control existing noxious weed infestations as well as to prevent new invasive species from infesting Yellowstone County.
Spotted KnapweedCentaurea maculosa Lam.
Sunflower family - Asteraceae
Photos from Montana Weed Control Association
Video Supplied By Ravalli County Weed District
| Attribute | Description |
|---|---|
| Growth Habit | Biennial or short-lived perennial, up to 3 ft. tall. Rosette formed first year, flowering stalk elongates second year. |
| Leaves | Long and divided below, short and narrow above. Covered with fine hair. |
| Stem | Erect with slender wiry branches. Covered with fine hair. |
| Flower | Seed heads mostly on branch tips, solitary to 1″ diameter. Pink to purple, rarely white. Seed head bracts are black tipped, with 5–7 pairs of short feathery appendages. |
| Roots | Taproot not well developed. |
| Seeds | Brownish, 1.8″ long, notched on one side of base, short tuft of bristles at tip end. |
| Reproduction | Seeds. |
| Habitat | Well-drained, light soils receiving summer rainfall. Rangelands. |
| Biological Controls | Sulphur knapweed moth (Agapeta zoegana), Knapweed root weevil (Cyphocleonus achates), Lesser knapweed flower weevil (Larinus minutus), Broad-nosed seed head weevil (Bangasternus fausti). |
| Herbicides | 2,4-D; 2,4-D & Tordon; Curtail; Milestone. |