Spotted knapweed
(Centaurea biebersteinii)
Herbaceous, short-lived perennial, 2-4’ tall. Persists as a rosette for 1-4 years before bolting. Flowering plants usually have 1-6 stems, but many have up to 20.
Other names for this plant include:
- Scientific names: C. stoebe; C. stoebe ssp. micranthos; C. maculosa
Classification in Wisconsin: Restricted
- Ecological Threat
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- Invades dry areas, including prairie, oak and pine barrens, dunes and sandy ridges. It also invades roadsides and disturbed areas.
- Roots exude allelopathic chemicals (compounds that inhibit the growth of other vegetation).
- It is not palatable as a forage plant and is avoided by livestock and native grazers.
- Infestations cause increased runoff, sedimentation, and decreased water-holding capacity in soil.
- Identification
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CAUTION: Wear long sleeves and gloves when handling. Spotted knapweed exposure can irritate the skin.
Leaves: Gray-green, covered in rough hairs, and deeply divided. Rosette leaves grow to 6” long. Stem leaves alternate, with lower stem leaves resembling rosette leaves, becoming small (1-3” long), entire and linear higher up the Stem.
Flowers: Thistle-like, pink to purple flower heads, rarely white. Flower heads have stiff bracts tipped with black, fringed hairs. Bloom mid-summer to early fall.
Fruits & seeds: Wind-dispersed for short distances but carried long distances by humans, livestock, or rodents. Viable in the soil for up to 7 years.
Roots: Strong taproot. Some plants produce a shallow mat of fibrous roots extending from the plant for several feet. Some sprouting from lateral roots occurs.
Similar species: Several non-native Centaurea species look identical. The bracts on the flower head can distinguish spotted knapweed tipped with black.
- Control
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Mechanical: Small infestations can be repeatedly hand-pulled making sure to remove the entire root. Before the seed-set, continuous mowing as close to the ground as possible may suppress populations.
Chemical: Foliar spray of glyphosate, clopyralid or aminopyralid and a non-ionic surfactant during bolting or flower bud stage.
Biological: There are currently 13 biological control agents. Successful treatment requires one seed head and one root mining agent. Contact the Wisconsin Department of Agriculture, Trade and Consumer Protection.
For more information on control techniques, visit the Spotted Knapweed factsheet [exit DNR] by the University of Wisconsin-Extension.
- Resources
- Sources for content:
- Czarapata, Elizabeth; Invasive Plants of the Upper Midwest: an illustrated guide to their identification and control. The University of Wisconsin Press. 2005. Pg. 52-55
- University of Wisconsin-Extension Weed Science
Links for more information:
