Spotted Knapweed - Centaurea biebersteinii

Description: Spotted knapweed is a biennial to short-lived perennial forb native to central Europe and Eastern Russia (Sheley et al. 1999). This species arrived in North America in the late 19th century as a contaminant in alfalfa seed and in soil used as ships ballast. The first record of spotted knapweed on the continent is from Victoria, British Columbia in 1883. Spotted knapweed may grow to 1.2 m in height and is less branched than diffuse knapweed and usually has darker red-purple flowers.

Type: biennial to short-lived perennial

Habitat and Impacts: Spotted knapweed grows in a wide range of dry habitats from grasslands to forests although it prefers open sites with well drained soils. Typically spotted knapweed occurs in areas that receive 30 to 50 cm of annual precipitation but does occur in drier areas. It is intolerant of complete shade. Usually invades disturbed sites but can then spread into adjacent undisturbed sites. Infestations can result in reduced yields of livestock forage and can displace native vegetation, particularly in areas of moderate grazing pressure.

Method of Spread: Spotted knapweed reproduced exclusively by seed and each plant can produce up to 140,000 seeds. Seeds are dispersed primarily by wind, but most seeds land close to the parent plant. Seeds can also be dispersed in cut hay or bedding or on vehicle undercarriages. The seed banks of spotted knapweed can be extremely large and take years to manage using any control method available.

Location: Widespread throughout the Cariboo Chilcotin Coast along corridors of transport and utility rights-of-way. Highest density of sites along main highways but scattered elsewhere over most of the region. Significant infestations in residential subdivisions throughout the region. The inventory for this species is well developed, although many secondary roads are known to contain unsurveyed spotted knapweed. There is a large infestation within the Thompson Nicola Regional District.

Management Options:

Mechanical: Handpulling or mowing prior to seed set with repeated treatments after the initial cutting.

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

Biological: Twelve different biocontrol agents have been used in British Columbia with good establishment and reduction in plant vigour. Success at removing plants and reducing densities in infestations is limited at this time to localized areas in the southern areas of the Province. Agapeta zoegana (Root feed moth), Cyphocleonus achates (Root feeding weevil), Larinus minutus and obtusus (seed feeding weevils), and Metzneria paueipunctella, (Seed feeding moth) have been released within the Cariboo Chilcotin.

CCCIPC Priority and Treatment Strategy: Priority 1 (new invader) in Nazko, Chilcotin & Central Cariboo, Priority 2 (containment) in all other regions. All sites west of the Fraser River will be eradicated. Sites east of the Fraser River will be managed on a site specific basis to reduce rate of spread and density of existing infestations along the main corridors near Hwy 97 and infested lands. Future containment lines may be considered in some heavily infested areas. A large percentage of the sites on the inventory map are monitoring only as the weed has been effectively controlled.

Treatment Options:

Local Level - hand- pulling small infestations and chemical where appropriate.
Landscape Level - chemical treatments, Hand pulling and biocontrol releases and monitoring effectiveness.

Spotted Knapweed flower

Spotted Knapweed plant

Spotted Knapweed biocontrol feeding on the flower head


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