Plumeless Thistle

Description

Plumeless thistle was introduced into North America in the late 1800s from Eurasia (Ball et al, 2006). It is a biennial tap-rooted thistle that grows up to 2 metres tall. The upper stems are branched and have spiny wings extending right up to the flower head. Flowers form at the top of the stems in clusters or singlets. The flowers are typically purple in color, although some are white/cream. This plant is often confused with Nodding thistle (Ministry of Agriculture, Lands and Fisheries, 2002).

Plumeless thistle has been known to hybridize with Nodding thistle when found inhabiting the same location (Ministry of Agriculture and Lands, 2002).

Type

Biennial forb

Habitat & Impacts

They prefer mid-elevations where they are often found inhabiting pastures, fields, logged areas, and roads sides (Ministry of Agriculture, Lands and Fisheries, 2002).

Method of Spread

This thistle is one of the more aggressive thistles resulting from its heavy seed production. A single plant can produce up to 9,000 seeds and seeds can remain viable in the soil for up to 10 years. Seeds spread predominantly by the wind.

Location

Sites have been confirmed in Williams Lake along the Williams Lake River Valley Trail (Not on Maps). It is thought to occur in the North Cariboo as well but this has not yet been confirmed.

Mechanical

Persistent and continual mowing, clipping, or hand pulling can reduce infestations by reducing plant vigour and seed production.

Chemical

Herbicides that contain picloram, dicamba, 2, 4-D, or glyphosate can be used to successfully manage this species. Herbicides should be applied in the spring prior to bolting or in the fall on new rosettes (Ministry of Agriculture and Lands, 2002).

Biological

Biological control agents are available for Plumeless thistle. These include Rhynocyllus conicus (weevil) and Trichosirocalus horridus (weevil). These weevils cause damage to the seed head and plant foliage.

CCCIPC Priority & Treatment Strategy

Priority 1 (new invader) throughout the region. The current management goal for Plumeless thistle in the Cariboo Chilcotin Coast region is elimination via chemical and mechanical treatment.

Local Level

Frequently hand pulling and/or mowing small infestations.

Landscape Level

Chemical application where appropriate.