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Biological controls for SPOTTED KNAPWEED coming soon.

Project information coming soon.




SPOTTED KNAPWEED — Centaurea maculosa Lam.

Asteraceae — (Sunflower family)

Spotted knapweed, an aggressive invader, is a biennial or usually short-lived perennial with a stout taproot. It forms a flowering stalk up to three feet tall during its second year. It can have one or more stems. Basal leaves up to six inches long, blades narrowly elliptic to oblanceolate, entire to pinnately parted; principal stem leaves pinnately divided. Flowering heads are solitary at end of branches; involucral bracts stiff and tipped with a dark comb like fringe. The ray flowers are pinkish-purple or rarely cream-colored. Fruits are about 1/8 inch long, tipped with a tuft of persistent bristles.

Spotted knapweed, which was introduced from Eurasia as a contaminant of alfalfa and clover seed, ranks as the number one weed problem on rangeland in Western Montana. Other Western states are experiencing a reduction in desirable plant communities as this species is allowed to spread. Knapweeds readily established themselves on any disturbed soil – by road building, development, logging, flooding or fire. Spotted Knapweed gets a jump on other plants with its early spring rosette growth taking most of the available space, sun, water and nutrients from other plants. The flowering period extends from June to October.

Seed head bracts are black tipped, with short feathery ends. Russian Knapweed has black scaly roots. Diffuse Knapweed is similar except it does not have spots on the bracts and has white flowers.  Knapweed species actually contain a chemical “herbicide” substance that prevents the growth of surrounding vegetation. Infestations of the species can reduce native grasses and forbs by as much as 90%. Knapweed is spread by wind, animals and people. This often happens when weeds “hitchhike” on vehicles.

Since knapweed does not hold soil nearly as well as native vegetation, erosion increases dramatically where knapweed dominates. So earth sloughs into streams and fouls spawning and rearing habitat as well as the essential forage base for wild mammals by undermining native plant diversity.

Growth Habit: Biennial or short lived perennial, up to 3` 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.

Other: Very aggressive, can infest large areas quickly, offers very little big game or livestock forage value.


Courtesy of Weeds of the West)