Black knapweed

Black knapweed

Fact Sheet

ALERT SPP This Plant is on high alert.


Latin Name: Centaurea nigra

Origin:  Europe

Physical Description: Perennial herb from a taproot. Stems are erect, branched, and covered with short hairs giving them a woolly appearance. Stems can grow up to 150 cm tall. Leaves are stalked, hairy above and below, lance-shaped and typically 15cm long and 3cm wide. Flowers are purple (sometimes white), thistle-like and are found singly at the end of stems and branches. The flowers are covered with stiff black/brown bracts with long black fringes.

Habitat: Prefers full sun and dry soils but can grow in a wide range of conditions. It is often found along roadsides and in meadows, pastures, and open areas.

Impacts:  It outcompetes native/desirable plants species resulting in reduced biodiversity and crop production. It can also alter the chemistry, preventing the growth of other plants and making pastures unpalatable to grazing animals.

Reproduction: It reproduces by seed and can regenerate from root crown or by rhizomes. Each plant can produce over 18,000 seeds per plant produced annually and seeds can remain viable in soil for at least five years.

Management Options

Mechanical: Hand pulling small infestations can be effective if the entire tap root is removed. If the entire root cannot be removed, the root must be cut at least 3cm below ground. Mowing or cutting plans can prevent seed set if carried out before flowering.

Chemical: Several herbicides with the following active ingredients can control Black knapweed: 2,4- D, aminopyralid, chlopyralid, picloram, triclopyr, triclopyr + chlopyralid, and glyphosate. For available products, contact your local agri-supply store. Prior to any herbicide application, read and follow the label instructions 

Biological: Larinus obtusus is a seed feeding weevil that was originally released to help control Spotted knapweed. It has since dispersed onto other knapweed species, including Black knapweed.

Scroll to Top