Canada Thistle
Management Prioritization
Identification
Common Name: Canada Thistle
Scientific Name: Cirsium arvense (L.) Scop.
Legal Status: Prohibited - Control
Efforts must be made to prevent seed maturation and dispersal of plants into new areas. Additionally, no transportation, propagation, or sale of these plants is allowed. Failure to comply may result in enforcement action by the county or local municipality. Minnesota Noxious Weed Law
Background
Canada thistle is native to Europe. It was introduced to North America in the 1600s, probably in agricultural seed shipments and is now widespread throughout the United States and Canada.
- Canada thistle is an aggressive perennial with a vigorous root system that continually produces new shoots, invading new areas and out-competing other vegetation types.
- Grows 2 - 5 feet tall.
Leaves
Leaves are alternate, lance shaped, irregularly lobed, and have wavy spiny/toothed margins.
Canada thistle leaf
Stem
Stems are usually smooth, but sometimes have short hairs and are slightly grooved.
Canada thistle stem
Flower
Flowers are purple and pink, occasionally white, and are borne at the end of the stems in clusters. Buds are 1/2 inch wide by 3/4 -1 inch long, have a tear-dropped shape, and lack spines.
Flowers begin to develop in late June, blooming between July and August.
Canada thistle flowers
Seed
This plant is most recognizable in mid-July when flowers change to seedheads with obvious white fluffy tops. Seeds are attached to the "fluff" and can become airborne and spread to new areas.
Canada thistle is a prolific seed producer and also spreads by roots.
Canada thistle mature flower head
Canada thistle seed
Seedling
Seedlings emerge as small rosettes in the fall or early spring, eventually bolting into erect branched flowering stems.
Photographer: Ohio State Weed Lab
Canada thistle rosette
Root
Canada thistle develops a widespread root and rhizome system quickly taking over an area.
P hoto: Purdue University, Department of Botany Plant Pathology
Distribution
Current Distribution Model
- Point data collected from EDDMapS; not all locations in the state have been recorded, but points on distribution map have been reported and verified.
- Distribution model takes location data and environmental factors into account to create a prediction of current distribution
- Canada thistle is widely distributed throughout the state with large populations reported throughout Minnesota.
Management Prioritization
Influenced by:
- distribution models
- actual reports
- economic benefits
- land cover
- conservation features
- trails
High priority areas surround areas of high density to prevent further large infestations and loss of biodiversity.
Infestation Examples
01 / 03
1
General Infested Area
Populations of Canada thistle are large and dense. Their large rhizome structure and ground cover prevent other plants from germinating and establishing.
Management here is involved.
2
Leading Edge
Sparse populations in the transition from infested areas to un-infested areas.
Management is involved but can prevent further spread or large establishment of stands.
3
Isolated Population
Location far from other known populations.
Management here is efficient and cost effective.
Lifecycle: Treatment timing
Treatment timing lifecycle for Canada thistle
Funding for this project was provided by the Minnesota Environment and Natural Resources Trust Fund as recommended by the Legislative-Citizen Commission on Minnesota Resources (LCCMR). The Trust Fund is a permanent fund constitutionally established by the citizens of Minnesota to assist in the protection, conservation, preservation, and enhancement of the state’s air, water, land, fish, wildlife, and other natural resources. Currently 40% of net Minnesota State Lottery proceeds are dedicated to growing the Trust Fund and ensuring future benefits for Minnesota’s environment and natural resources
