Invasive Plants and Agricultural Pest Management
Welcome to Alaska's Invasive Plant Program. Our program coordinates prevention, outreach, and management strategies for invasive plant issues through collaboration with land managers, agencies, organizations, and policy makers across Alaska. These efforts are guided by the implementation of our Strategic Plan and relevant noxious weed regulation and policy. Our goal is to help keep Alaska's pristine landscapes and natural resources free from impacts of noxious and invasive plants.
Canada thistle (Cirsium arvense)
Identified as a prohibited noxious weed in Alaska (11 AAC 34.020), and in 34 other states.
The Alaska State Department of Natural Resources (DNR), Department of Agriculture classifies Canada thistle as a Top Priority invasive species for control, eradication and prevention.
- Taking Action
Grows 1-4 feet tall
Flowers are typically purple, but can be white or pink; bracts are tipped with prickles,
Leaves are distinctively spiny, lance-shaped, wooly hairs on the underside and hairless on top
Deep, wide-spreading roots
The only thistle that is dioecious (separate male and female plants)
Canada thistle is not native to Alaska and it threatens natural plant communities by directly competing for resources and displacing native vegetation. Canada thistle plants produce allelopathic chemicals which can inhibit the growth of other plants in close proximity. It's dense, rhizomatous growth has the potential to impact natural and agricultural resources statewide.
Displaces native vegetation through competition for nutrients
Decreases agricultural production
Destroys yards, gardens, and parks
Degrades natural habitats
Expensive to manage
Habitat: Fields, pastures, meadows, roadsides, and disturbed areas. Common at low to middle elevations, mostly in agricultural areas.
To help prevent the spread of Canada thistle:
Report any sightings to 1-877-INVASIV
Organize neighborhood weed pulls
Pass the word along about C. thistle to neighbors
Use Weed Free Hay and Straw
Wash your vehicle before re-entering the state
Check pet fur for seeds before leaving an area
Check potted plants for invasives growing in their pots before you purchase
View our Canada thistle rack card by clicking on the image below: