Spotted Knapweed

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 more than one metre in height. It is less branched than diffuse knapweed and usually has darker, red-purple flowers.

Type

Biennial to short-lived perennial

Habitat & 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 transportation corridors and utility rights-of-way. The highest density of sites is along main highways, but it is also scattered elsewhere over most of the region. There are 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.

Mechanical

Hand pulling 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 & 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 the 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.

Local Level

Hand pulling small infestations and chemicals where appropriate.

Landscape Level

Chemical treatments, hand pulling, and biocontrol releases and monitoring effectiveness.