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Invasive Plants
- Perennial Sow Thistle
- Creeping Thistle
- Oxeye Daisy
- Common Tansy
- Spotted Knapweed
- Narrowleaf Hawksbeard
- Scentless Chamomile
- Leafy Spurge
- Foxtail Barley
- Altai Wild Rye
- Crested Wheat Grass
- Smooth Brome
- Quackgrass
- Reed Canary Grass
- Bird Vetch
- Lucerne
- Sweetclover
- Greater Butter-and-Eggs
- Dalmatica Toadflas
Perennial Sow-Thistle
Common Name: Perennial Sow-Thistle
Scientific name: Sonchus Arvensis
Family: Asteraceae
Description
Despite the name, sow-thistles more closely resemble giant dandelions than they do the true thistles. Perennial sow-thistle is considered a noxious weed throughout most of its range. This is an invasive species able to spread long distances by wind-blown seed. It is perennial with rhizomes that grow up to 10 feet deep that are very difficult to remove by hand. It is particularly a problem for agricultural producers. In natural areas it has been known to invade beaches and lakeshores.
Range in Yukon
Primarily in the Whitehorse area as far north as Carmacks but has been reported from Destruction Bay, Johnson's Crossing and the Kotaneelee gas plant; found commonly along highway corridors.
Similar Species
Spiny sow-thistle (Sonchus asper) is known only from Haines Junction and the Labiche River. This is an annual plant with a short taproot. Narrowleaf hawksbeard (Crepis tectorum) is another annual plant with short taproots. It occurs throughout the Yukon.
Ecological Impact
Perennial sow-thistle may modify or retard the successional establishment of native species. At high densities in can dramatically reduce water resources and possibly decrease native plant diversity.
Control
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.
Contact Environment Yukon Government of Yukon Box 2703 (V-5N) Bruce Bennett, Wildlife Viewing Biologist Phone: 867-667-5331 Email: bruce.bennett@gov.yk.ca |