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Yellowstone County, Montana
Noxious Weed
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Spotted Knapweed
(Centaurea maculosa Lam.)

Sunflower family - Asteraceae


Spotted Knapweed
Photo by Tom Whitson, Roy Reichenbach

Produced by Wyoming Weed & Pest Council in cooperation with Sandoz Crop Protection Corp.

Spotted Knapweed Rosetta

Spotted Knapweed Branch

Spotted Knapweed Leaves

Spotted Knapweed Bloom 1

Spotted Knapweed Bloom 2

Spotted Knapweed Patch

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 to 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.


Video Supplied By Ravalli County Weed District