Coastal Invasive Species Committee

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Diffuse Knapweed

Centaurea diffusa

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CONTAIN

Family: Asteraceae (Sunflower).

Other Common Names: Spreading knapweed, tumble knapweed.

Origin: Eurasia.

Growth Form/Reproduction: Biennial. Seeds.

Legal Status: Weed Control Act, Forest and Range Practices Act, Community Charters Act.

Impacts:
Agricultural: Reduces forage production for livestock and wildlife. Can infest hay crops, reducing value and productivity.
Ecological: A pioneer species that can quickly invade disturbed plant communities, reduce biological diversity.
Human: Dense stands reduce access to recreational areas.

Habitat: Poorly adapted to cultivation or moist sites. Disturbed sites, pastures, roadsides, utility corridors.

Status and Distribution: Common in Nanaimo. Not known in Powell River or Strathcona. Spot occurrences in remaining Regional Districts. Found in CDFmm, CWHxm and CWHvh.

Management Strategy: Hand-pulling can be effective to eradicate new, small patches. Picloram, dicamba, clopyralid, glyphosate and 2,4-D are all effective on seedlings, rosettes and mature plants. Two biocontrol agents have been released on Vancouver Island for this species, which are monitored by the Ministry of Forests and Range.