Diffuse Knapweed - Centaurea diffusa

Description: Diffuse knapweed is a biennial or short-lived perennial with well developed taproot and highly branched stems introduced to North America from Eurasia near the beginning of the 20th century probably in alfalfa seeds (Roche and Roche 1999). It grows to 60 cm tall and has white, lavender, or purple composite flowers.

Type: biennial or short-lived perennial

Habitat & Impacts: It is found in a variety of dry habitats particularly in disturbed areas and does not tolerate shade. It is generally not found in cultivated or irrigated fields. Diffuse knapweed is unpalatable to livestock, and can cause serious loss of forage production on heavily infested rangelands.
Method of Spread: Diffuse knapweed reproduces exclusively from seeds and a single plant can produce up to 18,000 seeds. Most seeds fall close to the parent plant, but adult plants may break of at the root collar or lower stem and tumble for a considerable distance blown by wind and distribute seeds this way. Seeds can remain viable in the soil for many years.

Location: Scattered throughout the region but heaviest along Highway 97 and at Green Lake, Konni Lake and in Tatlayoko Valley. There is a large infestation to the south and east of our region.

Management Options:

Mechanical Control: Cutting or mowing prior to seed-set can reduce seed production, but cut plants may survive, re-bolt, and produce additional seed heads. Handpulling can be effective on small infestations, but must be repeated depending on the size of the initial population.

Chemical Control: Chemical treatments consist of Picloram, 2, 4-D, Aminopyralid and Glyphosate, and applied before flower production.

Biological Control: Successful release and establishment of a number of biocontrol agents has reduced the vigour and abundance of diffuse knapweed in other regions of British Columbia. Larinus obtusus, Larinus minutus,are seed weevils, and Cyphocleuns achates is a root weevil that have been released in the region.

CCCIPC Priority & Treatment Strategy: Priority 1 (new invader) in Nazko, Chilcotin, and entral Coast, Priority 2 in all other areas (containment).

Treatment Options:

Local Level - hand-pulling small sites, herbicide for larger sites
Landscape Level - herbicide, biocontrol if larger infestations occur.

Diffuse Knapweed flower.

Richard Old, XID Services, Bugwood.org

Diffuse Knapweed plant.

Richard Old, XID Services, Bugwood.org

Diffuse Knapweed rosette.


Invasive species profile taken from the Cariboo Chilcotin Coast Invasive Plant Committee Invasive Plant Regional Strategic Plan

Page last modified: October 30, 2018 09:44:02 PDT