Creeping Thistle (Yukon Invasive Species Guide)

Creeping Thistle

Cirsium arvense

Description ³

Creeping Thistle or Canada Thistle is native to Europe, Asia and Africa. This perennial plant can form new shoots from deep and extensive horizontal roots. It is one of the most invasive species in North America and is a noxious weed in most jurisdictions throughout Canada and the USA, including Alaska. Male and female flowers occur on separate plants.

Range in Yukon ³

Known from the Haines Highway just south of Haines Junction, the Takhini Hotsprings and the La Biche River. It has occasionally been found in potted garden plants in Whitehorse.

Similar Species ³

Elk Thistle (Cirsium foliosum) is a rare native species found throughout southern Yukon. It is often persecuted because it is mistaken for an introduced thistle. Elk Thistle is a biennial (flowers in the second year than dies) with a large flower head, and a stout carrot-like taproot. Elk Thistle grows in wet areas, usually near rivers.

Ecological Impact ³

Creeping Thistle competes directly with native plants for nutrients and water; it also produces chemicals that help displace native vegetation. It is an aggressive agricultural weed that has the potential to reduce crop yields by 100%. Due to its abundant and flammable leaf litter it can increase fire frequency and severity.

Control ³

Because the root system is usually well developed, it is almost impossible to dig out. Therefore perennial plants require depletion of nutrient reserves in the root system, prevention of seed production, and prevention of dispersal. If roots are cut or broken off new plants may sprout. Mowing or cutting to reduce root reserves and seed production should be done a few times a season for several years. When hand-pulling use a shovel and remove as much of the root as possible. When cut, flowering plants will continue to produce seeds. Plant material should be put in a clear plastic bag and placed in the sun until the roots and seeds are cooked.

For more information visit: Yukon Invasive Species Council

Sources and Credits

More Info

Range Map

iNaturalist.ca Map

Plant	Daisy Family (Asteraceae)
Color	pink

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