Brown Knapweed
Centaurea jacea
Washington State Classification
Class B — Control Required (Designated)
Knapweed invasions have many impacts including an increase in production costs for ranchers, degrading wildlife habitat, crowding out desirable forage, decreasing plant diversity, increasing soil erosion rates, and posing wildfire hazards.
Required control in Region 1 (all western Washington counties)
Quick Reference
Identification
Growth Habit
Brown knapweed is a perennial plant with a woody root crown that grows 20 to 48 inches tall, branching near the top.
Leaves
Leaves are egg-shaped or lance-shaped and undivided. Leaves become smaller moving up the stem.
Flowers
Flowers are rose to purple and rarely white. Flower heads are ¾ to 1 inch, light to dark brown. Hairy bracts at base of flower heads are wider at the tips. They have broad, thin, papery margins. The center of each bract is dark brown.
Fruit & Seeds
Seeds are tan, small with fine hairs and no pappus.
Impact
Knapweed invasions have many impacts including an increase in production costs for ranchers, degrading wildlife habitat, crowding out desirable forage, decreasing plant diversity, increasing soil erosion rates, and posing wildfire hazards.
Ecology & Spread
Habitat
Brown knapweed grows on roadsides and in meadows, pastures and open areas. Please click here to see a county level distribution map of brown knapweed in Washington.
Spread Mechanisms
Reproduction
Brown knapweed reproduces by seed and can regenerate from the crown.
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Control Methods
Biological Control
- Urophora quadrifasciata, a seed head gall fly, has been used at a few, limited brown knapweed sites in Washington.