Spotted knapweed is a member of the Aster family, Thistle tribe. Native to central Europe, it is a simple perennial that reproduces from seed and forms a new shoot each year from a taproot. The plant can have one or more shoots up to four feet tall.
Rosette leaves can be six inches long and deeply lobed. Leaves on shoots are smaller and finely divided, becoming smaller toward the top of the shoot, and are covered with fine hair. Flowering heads aresolitary and occur on shoot tips. They are up to one inch in diameter.Flower color usually is lavender to purple. Seed heads bracts are stiffand black-tipped, with five to seven pairs of short, feathery appendages. Seeds germinate in spring or fall. Perennial plants resume growth in early spring and bolt at approximately the same time as diffuse knapweed. Flowering occurs throughout the summer into fall.Spotted knapweed occupies dry meadows, pasture land, stony hills,roadsides, and the sandy or gravelly flood plains of streams and rivers,where soils are light-textured, well drained, and receive summer precipitation. Spotted knapweed tolerates dry conditions, similar to diffuse knapweed, but will survive in higher moisture areas as well.
This weed is not preferred by elk and severely reduces available forage on their ranges. Mule deer brows Spotted knapweed during late summer and fall thereby contributing to the spread of seeds to new locations. Each plant can produce from 1400 to 2400 seeds each season with over a 90% germination rate. Seeds can remain viable in the soil up to 8 years. Spotted knapweed patches can increase in area up to 27%annually.
Spotted knapweed Fact/Info Sheet (PDF) Click Here
Look for previous years "skeletons" near the new infestation. Bag and dispose of the old plants.