Brown knapweed

Brown knapweed

Fact Sheet

ALERT SPP This Plant is on high alert.


Latin Name: Centaurea jacea

 Origin:  Europe

Physical Description: Perennial herb from a taproot. The stems are erect, branched, glabrous or somewhat woolly. They typically grow 0.1-1.2 m tall. The Leaves are egg-shaped or lance-shaped, undivided and have waxy margins and a hairy texture. Basal leaves may be stalked, lobed or toothed and become smaller moving up the stem. Flowers are rose to purple (rarely white) and have bracts that have dark brown bases.

Habitat: Prefers sunny areas with mesic to dry soils. It’s often found along roadsides and in grasslands, orchards, cultivated fields, open woods, meadows, pastures and woodland clearings.

Impacts:  It outcompetes desirable species to form large monocultures impacting forage quality, species diversity and wildlife habitat are reduced. It can hybridize with other knapweeds, allowing for aggressive seed dispersal. This plant is toxic to horses when consumed. Horses typically avoid consumption of knapweeds in field/pasture settings however it can be inadvertently consumed in contaminated hay.

Reproduction:  It reproduces by seed and can regenerate from the root crown. Plants produce up to 800 seeds per plant and seeds can disperse as far as 20 feet from the parent plant.

Management Options

Mechanical: Hand pulling or digging up small infestations can be effective. It’s important to remove the entire root system to prevent regrowth from the root crown. Mowing is not recommended as plant will continue to grow and flower below mower blade.

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

Biological: Urophora jaceana is a seed feeding fly that emerge in July. U. jaceana was released in three field locations in Seymour Arm and Salmon Arm of the Shuswap area. Repeated monitoring has revealed no sustained population of a released agent.

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