Latin Name: Cirsium palustre

Physical Description: Marsh plume thistle is a biennial tap-rooted forb growing up to two metres tall with a cluster of large purple-pink flowers and bracts with large spines.

Type: Biennial

Habitat & Impacts: Marsh plume thistle grows on moist to wet areas on most soil types, provided seepage is present. Typically, this species grows in unshaded sites but can tolerate some shade. Marsh plume thistle can invade undisturbed riparian areas and moist pastures and reduce or eliminate native vegetation and reduce ecological functioning in these sensitive sites. This species generally does not pose a risk to agricultural crops as it does not tolerate cultivation but may pose a risk to forestry plantations by overtopping and then pressing and/or shading seedlings.

Method of Spread: Marsh plume thistle reproduces exclusively from seed dispersed by wind, water, or birds. Seeds can travel large distances, especially in area with strong consistent winds. It is unknown how long seeds remain viable in the soil.

Mechanical: Hand-pulling or mowing can prevent seed set and may be effective at removing infestations if repeated over several years.

Chemical: Clopyrlid and Aminopyralid are being used in the region.

Biological: No biocontrol specific to plume thistle is available, but a generalist seed-eating weevil, Rhynocillus conicus, is being evaluated in British Columbia.

CCCIPC Priority & Treatment Strategy: Priority 1 (new invader) Marsh plume thistle is ranked as a new invader, although it is only present in the North Cariboo at this time. All known and new sites will be managed for the goal is to eliminate all sites in the region and stop all new sites from becoming established. The Northwest Invasive Plant Council has drawn a containment line north of this region and is actively attempting to stop the spread of this difficult to manage species.

Local Level: Hand-pulling

Landscape Level: Hand-pulling or chemical