Spotted Knapweed (State designated weed)

Spotted Knapweed (State designated weed)

• Centaurea stoebe
• Asteraceae (Sunflower family)

Spotted knapweed, which was introduced from Eurasia as a contaminant of alfalfa and clover seed, ranks as the No. 1 weed problem on rangeland in Western Montana. Other Western states are experiencing a reduction in desirable plant communities as the species spreads.

Growth Habit: Biennial or short lived perennial, up to 3 feet tall. Rosette formed first year, flowering stalk elongates second year.

Leaves: Long and divided below, short and narrow above. Covered with fine hair.

Flowers: Seed heads mostly on branch tips, solitary, to 1 inch diameter. Pink to purple, rarely white. Seed head bracts underneath the flowers are black tipped, giving them a spotted appearance. Flowers from June to October.

Roots: Taproot, not well developed.

Other: Very aggressive, can infest large areas quickly, offers very little big game or livestock forage value. Also, since spotted knapweed does not hold soil nearly as well as native vegetation, erosion increases dramatically where knapweed dominates.

Status: State Designated Noxious Weed, Category 2: Localized. No tolerance of new infestations and aggressive control on all known infestations.

Control: Mechanical control (hand pulling) of the rosette and bolting plant is effective. If flowering, bag and dispose of the plants and take great care to avoid spreading seeds. Wear gloves to avoid skin irritation. Biological controls have produced mixed results. Chemical controls are effective. FCWP offers a 40 percent Cost Share on chemicals for controlling this species. Contact your local weed and pest office for further treatment recommendations.

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