Plumeless Thistle - Carduus acanthoides

Description: Plumeless thistle was introduced into North America in the late 1800’s from Eurasia (Ball et al, 2006). It is a biennial tap rooted thistle that grows 1-2 meters tall. The upper stems are branched and have spiny wings that extend 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 and 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 tot 10 years. Seeds spread predominantly by 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.

Management Options:

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 and 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.

Treatment Options:

Local Level – frequently hand pulling and/or mowing small infestations.
Landscape Level – Chemical application where appropriate.

Richard Old, XID Services. Inc.,

Plumeless Thistle plant

Todd Pfeiffer, Klamath County Weed Control,

Plumeless Thistle 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