Meadow knapweed is a threat to forage production in pastures and grass hay. As with the other knapweeds, it is undesirable because of its low palatability and its persistence where it replaces desirable forage plants.

Meadow knapweed was reportedly grown at one time as a forage species in Oregon. It is leafier and more palatable to livestock than spotted or diffuse knapweed. However, both palatability and nutritional value decline as the plant matures. It does not appear to tolerate heavy grazing, although it continues to flower and produce seed on shorter plants when periodically grazed.

The earliest records in the Pacific Northwest are from western Oregon in 1911 and 1918. It was present in western Washington by the early 1920s. The infestations in Washington are currently estimated in excess of 3000 acres. Meadow knapweed appears to be another "weed on the move."

Meadow knapweed is a fertile hybrid between brown knapweed and black knapweed. Characteristics vary between those of each of the parents, with individual plants in a population more closely resembling black or brown knapweed.

Brown and black knapweed are native to Europe. Hybrids between the two species also occur there.

Meadow knapweed is a perennial from a woody crown. It reproduces by seed.

The upright stems, mostly 20 to 40 inches tall, branch from near the middle. Unlike spotted and diffuse knapweed, meadow knapweed leaves are not finely divided. Leaves may be up to 6 inches long and 1¹/₄ inch wide; leaf margins are mostly entire or have small lobes or teeth. Leaves on the stems are progressively smaller; uppermost ones are linear, almost bractlike.

Flower heads are solitary at the tips of the branches, about the size of a nickel, much rounder than spotted knapweed heads. Flowering occurs in summer; mid-July through August, continuing into November in western Washington as weather permits. Flowers are rose-purple, occasionally white.

Bracts surrounding the flower head are light to dark brown, with a papery fringed margin. At the time of flowering, the bracts reflect a metallic golden sheen.

Seeds are about ¹/₈ inch long, ivory-white to light brown. A row of short hairs may be present at the end opposite the narrowed point of attachment.

Seedlings are tap rooted; mature plants develop a cluster of somewhat fleshy roots below the woody crown.

Proper pasture management is necessary for long-term control of meadow knapweed. This includes irrigation, grazing management, fertilization and use of herbicides as needed.

PREVENTION.
Prevent meadow knapweed from becoming established. Learn to identify it and avoid driving through infested areas. Check purchased hay and fields or pastures from which equipment or livestock move onto your property. Use weed screens on irrigation water intake and work with irrigation districts to prevent meadow knapweed seeds from entering the water. Seed all disturbed sites to a perennial cover immediately after any soil disturbance.

CULTURAL.
Dig out initial infestations of only a few plants. Plants that are periodically mowed continue to flower and produce seed on shorter plants, prolonging the season of growth and flowering. Where feasible, cultivate infested pastures and rotate through an annual hay crop, green manure or some other cleanup crop before reseeding to the desired permanent forage species. Meadow knapweed does not tolerate repeated cultivation, but may resprout following the initial breakup of the crown and fleshy roots. Consider the seed reserve in the soil. Where residual forage grasses are adequate, meadow knapweed may be controlled using herbicides and fertilizer. Following establishment of the desired forage species, manage the livestock, rotating stock as necessary to prevent overgrazing. Undermanagement is the precursor of overgrazing.

CHEMICAL.
For specific recommendations, refer to the Pacific Northwest Weed Control Handbook, an annually revised Extension publication available from the Extension Services of Oregon State University, Washington State University, and the University of Idaho.

BIOLOGICAL.
The UV wing gall fly (Urophora quadrifasciata), introduced to control spotted and diffuse knapweed, uses the heads of meadow knapweed. Galls replace some of the seeds in the heads, lowering seed production. As yet this has not reduced the size of established weed populations. Seed production averaged 50 seeds per head in an area where this fly is established.