Nodding Thistle

Description

Nodding thistle is native to Europe and Asia and was introduced into North America in the early 1900s as a seed contaminant (Ball et al, 2006). It is an herbaceous biennial that can grow up to 1.5m tall. It produces a long fleshy taproot and from one to several erect and highly branched stems. The stems are spiny and winged except below the flower head. The leaves are deeply lobed and alternate on the stem. A single large pink/purple flower head is produced at the tops of the branches. The flower heads tend to droop down or “nod” at maturity (Cranston et al. 2005). This plant is often confused with Plumeless thistle.

Type

Biennial forb

Habitat & Impacts

Nodding thistle prefers mid elevation where it occurs in meadows, rangelands, roadsides and cut blocks. It can out-compete native plants and reduce pasture production. Nodding thistle is rarely eaten by livestock (Ministry of Agriculture, Lands, and Fisheries, 2002).

Method of Spread

Nodding thistle reproduces primarily by seed. A single flower head can produce up to 1,200 seeds and the seeds can remain viable in the soil for up to 10 years (Alberta Fish and Game Association, 2006).

Location

There are several nodding thistle sites in the Cariboo Chilcotin Coast region. These are located south of Alexis Creek and Hanceville, and along the Taseko Lake Road, Vert Lake, Chimney Creek and Ahbau Road.

Mechanical

Persistent and continual mowing, clipping or hand pulling can reduce infestations by reducing plant vigour and seed production. When hand pulling or digging it is important to completely remove the crown so the plant does not re-bolt.

Chemical

Chemical treatment is also highly effective in controlling Nodding thistle. Clopyralid, 2, 4-D or dicamba can be used to manage plants in the spring prior to bolting. Picloram has been shown to be effective on rosettes during fall application (Ministry of Agriculture and Lands, 2002).

Biological

Biological control is available for Nodding thistle in British Columbia. The agents that are used include Rhynocyllus conicus (weevil), Trichosirocalus horridus (weevil) and Urophora solstitialis (fly). These insects damage the seed heads and foliage of the plant, reducing seed production and plant vigour.

Rhinocyllus conicus and Trichosirocalus horridus agents have been released on most of the Nodding thistle sites in the Cariboo Chilcotin Coast region. They have successfully reduced vigour and spread of individual plants and infestations.

CCCIPC Priority & Treatment Strategy

Priority 4 (biocontrol) for all areas except the Central Coast where it is Priority 1 (New Invader). Existing and new sites will be managed primarily by biological control to prevent further spread. Small infestations may be treated chemically.

Local Level

Frequently hand pulling and/or mowing small infestations.

Landscape Level

Biocontrol releases, and chemical treatment on localized areas where appropriate.