ST. LAWRENCE EASTERN LAKE ONTARIO PARTNERSHIP FOR REGIONAL INVASIVE SPECIES MANAGEMENT
Brown Knapweed (Centaurea jacea) is a perennial plant that grows 1-4 ft in height and threatens the biodiversity of grasslands, open woods, meadows, pastures, and woodland clearings. It is native to Europe and was introduced to North America as forage, but it has low palatability and nutrition.
Brown knapweed outcompetes native vegetation, forming monocultures that reduce forage quality, species diversity, and wildlife habitat. Each plant can produce up to 800 seeds that spread by wind, water, wildlife, equipment, and human activity, contributing to its rapid expansion. Its presence also increases soil erosion.
Brown Knapweed is known to occur in the following counties in SLELO PRISM: Jefferson, Lewis, Oneida, and Oswego. There are also unconfirmed iNaturalist reports in St. Lawrence County.
Brown Knapweed prefers sunny, moist, cool areas but can tolerate some shade.
Leaves are alternate, lance-shaped and somewhat hairy, occasionally with wavy margins (leaf edges) or lobed. They are up to 10 inches long and 1 inch wide at the base of the plant and progressively get smaller as they go up the stem.
Flowers range from pink to purple in color, and sometimes have white centers. They are located at the ends of branches and are about 1 inch in diameter. Flowering occurs from mid-summer until fall. The brown bracts below the flowers are rounded and wide at the tip and often have brown tips.
Fruit is a dry seed, elliptic, brown, finely hairy, and usually lacks a tuft of hairs at the tip.
Brown knapweed has no closely related native look-a-like species. Spotted knapweed, another, invasive species, is similar in appearance, but the leaves are more deeply lobed, and the flowers have bracts that are stiff and marked with upside down “V”s, producing a spotted like appearance.
Effective management of Brown Knapweed (Centaurea jacea) relies on an integrated approach that combines manual, chemical, and biological methods to halt seed production and eliminate root crowns. Control strategies include hand‑pulling small infestations, applying herbicides such as clopyralid or 2,4‑D in spring or fall, and introducing biological control agents like gall flies.
For best results, a combination of the methods outlined below, tailored to the specific site, should be used.
Prevention is the first and preferred approach when managing any invasive species. Being aware of and able to identify invasive species is crucial for successful prevention.
If possible, monitor and manage the plants in the spring and early summer, before seed set, to prevent spread. If you do need to monitor or manage this species during seed set, prevent spread by cleaning equipment, vehicles, and footwear before transportation from brown knapweed-infested areas.
Hand-pulling and mechanical removal may be used to control populations.
Chemical Treatment: The use of herbicides in water is regulated; always consult state and local regulations for required permits.
Biological Control:
Take a clear, close-up photo, note the location (GPS coordinates are best), and report observations to NYiMapInvasives or directly to the SLELO PRISM’s Terrestrial Restoration and Resiliency Coordinator, Robert Smih, at robert.l.smith@tnc.org.
Education and stewardship are the most effective ways to prevent the spread and introduction of invasive species. You can help by joining our Volunteer Surveillance Network. Participants learn how to recognize, report, and monitor for priority terrestrial and aquatic species.