Latin Name: Carduus acanthoides

Origin:  Eurasia

Physical Description: It is a winter annual or biennial herb. It has a single stem that can grow up to 100 cm tall. The stem is covered with winged ridges bearing 3-5mm spines. The bluish-green leaves are elliptic to lance-shaped with toothed margins that contain terminal spines that are 2-5mm long.  The leaves are woolly with stiffer hairs along the vein. The pink to purple flowers are solitary or clustered at stem and branch ends.

Habitat: It prefers sandy loam soils that receive early season precipitation. It is often found along road, trail, and railroad rights-of-way, pastures, rangeland, gravel pits, vacant lots, and field edges.

Impacts: It can out-compete desirable plants creating monocultures and reducing overall biodiversity. In a pasture and rangeland setting, it reduces the availability of desirable forage for livestock and other wildlife. This plant can be toxic to livestock as it accumulate poisonous levels of nitrates when drought stressed, however livestock generally will not eat it because of the spiny stems.

Reproduction: It reproduces by seed only.  A single plant can produce up to 9,000 seeds that can remain viable in the soil for up to 10 years. The seeds have a parachute-like shape that allows the plant to disperse and reproduce effectively in the direction of the wind.

Mechanical: Flower heads can be removed to eliminate seed production. Repeated cultivation, digging or cutting can be effective. Mowing is most effective if completed before the first terminal buds bloom. Small infestations can be hand pulled or dug prior to seed set. All control methods will need to be repeated annually to deplete the seed bank.

Chemical: Several herbicides with the following active ingredients can control Plumeless thistle: 2,-4-D, Aminopyralid, Chlosulfuron, Cloypyralid, Dicamba, Picloram, and Metsulfuron.  For available products, contact your local agri-supply store. Prior to any herbicide application, read and follow the label instructions

Biological: There are several agents that have established and are available for control:

• Larinus carlinae – Seed feeding beetle (weevil)
• Rhinocyllus conicus – Seed feeding beetle (weevil)

Additional biological control agents have been introduced to BC for Plumeless thistle control however they are either limited in distribution of have not yet established.

Additional Resources:

Alberta Invasive Species Council Plumeless Thistle Factsheet

Provincial Biological Control Agents and Host Plants-Online Resource