Description

Spotted knapweed is a biennial herb in the aster family. It grows in tufted clumps, one plant giving rise to 1 to 20 slender, upright stems 1 to 3 feet in height with most branching occurring in the upper half. Seedlings form a rosette of pinnately to bipinnately dissected leaves 4 to 8 inches long. Stem leaves are pinnate low on the stem, and become small, linear-shaped further up the stem. White to pink or purple flowers are at the end of the stems in thistle-like heads. This species closely resembles another less widespread invasive, short-fringed knapweed (Centaurea nigrescens). Spotted knapweed has ^{-been renamed by plant taxonomists and is now known as Centaurea bierbersteinii DC.}

Habitat
Spotted knapweed grows in dry sterile, gravelly, or sandy openings such as pastures, old fields, and roadsides.

Distribution
Introduced accidentally into the United States from Europe late last century. It was possibly mixed in with alfalfa seed or in the ballast of ships, spotted knapweed has spread throughout the Northeast and Mid-Atlantic states, and westward to Kansas and Nebraska. It has also become established in the Northwest, where it infests overgrazed pasture. It has also spread throughout Canada, where it is found from Nova Scotia to British Columbia. It is found state-wide in Virginia.

 

Threats

Spotted knapweed shares with many other invasive species the ability to colonize disturbed areas. Once established it may infest neighboring habitats that are relatively undisturbed or in good condition. Infestation generally leads to a decline in biodiversity, because the invasive plant chokes out native vegetation. Grazing animals pass over it in favor of more palatable native grasses and herbs. The root system of this plant does not hold soil as well as native vegetation. Studies have monitored a significant loss of soil on sites infested with this species compared to sites With native vegetation.

Control
Hand-pulling, grubbing or clipping may provide some control of light infestations. On sites where feasible, mowing or hand-cutting early in the flower stage may control spotted knapweed. This process must be repeated over several years. Plants are less likely to sprout or regrow if allowed to bolt before cutting. Although more labor intensive, hand-cutting with a sharpened shovel will ensure that all flower buds are destroyed. For more information, contact the Virginia Department of Conservation and Recreation or the Virginia Native Plant Society at the addresses listed below.

 
For more information, contact the Department of Conservation and Recreation or the Virginia Native Plant Society.

DCR
Department of Conservation &. Recreation
Conserving Virginia's Natural and Recreational Resources
1500 E. Main Street, Suite 312, Richmond, VA  23219
(804) 786-7951

Virginia Native Plant Society
P.O. Box 844. Annandale, VA 22030