Thistle, Canada, Cirsium arvense

Life Cycle

Perennial

Propagation

Reproducing by seed and by horizontal stems.

Stems

Stems erect, 30 - 150 cm high, usually branched, slender, smooth or occasionally with a few, narrow, spiny-margined leaf-like wings on the lower part.

Leaves

Leaves more or less lobed and spiny, alternate (1 per node), elliptic to oblong in outline, stalkless and often clasping the stem; the wide variations in lobing, spininess, hairiness, texture and colour of leaves divide the species into 4 botanical varieties.

Flowers and Fruit

Flower heads numerous, comparatively small, 5 - 15 mm wide and about twice as long, the involucral bracts (b) weakly spiny or almost smooth; ray florets absent but disk florets (c) prominent with purplish or sometimes white corollas; plants unisexual; although stamens and stigmas are sometimes present in the same flower, the flowers are functionally unisexual, all the flowers in 1 head and all the heads on 1 plant being either male or female; heads with male (pollen-producing) flowers somewhat shorter and narrower than heads with female (seed-producing) flowers; seeds light brown or straw-coloured, smooth, 2.5 - 4 mm long. Flowers from June to late autumn.

Roots and Underground Structures

An extensive rhizome system.

Habitat

Found in numerous different habitats throughout Canada.

Competitiveness

.

Distinguishing Features

Canada thistle is a highly variable species, especially in leaf characteristics that seem to fall into four groups that have been given varietal status: 1) Spiny Canada thistle, Cirsium arvense (L.) Scop. var. horridum Wimm. & Grab. 2) Entire-leaved Canada thistle, Cirsium arvense L. var. integrifolium Wimm. & Grab. 3) Canada thistle, Cirsium arvense L. var. arvense and 4) Woolly Canada thistle, Cirsium arvense L. var. vestitum Wimm. & Grab.

Toxicity

Canada thistle is not known to be toxic.

Human Health Issues

Canada thistle is not a known allergen.

Forage Quality

No information exists at this time.

Species Benefits

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Power Ranking Corn

Power Ranking

↑ 20

 

Power Ranking Soybeans

Power Ranking

↑ 17

 

Biological Control

BIOCONTROL AGENT The stem gall fly (Urophora cardui) WHAT DOES IT DO? See complete report for more information. AVAILABILITY http://www.mcclay-ecoscience.com/agents.htm for availability. _________________________________________________ BIOCONTROL AGENT The stem weevil (Hadroplontus litura) WHAT DOES IT DO? See complete report for more information. AVAILABILITY http://www.mcclay-ecoscience.com/agents.htm for availability. _________________________________________________ BIOCONTROL AGENT The defoliating beetle (Lema cyanella) WHAT DOES IT DO? See complete report for more information. AVAILABILITY http://www.mcclay-ecoscience.com/agents.htm for availability. _________________________________________________ BIOCONTROL AGENT The seed-head weevil (Rhinocyllus conicus) WHAT DOES IT DO? See complete report for more information. AVAILABILITY http://www.mcclay-ecoscience.com/agents.htm for availability. _________________________________________________ BIOCONTROL AGENT The root-crown weevil (Cleonis pigr) WHAT DOES IT DO? See complete report for more information. AVAILABILITY http://www.mcclay-ecoscience.com/agents.htm for availability. _________________________________________________ BIOCONTROL AGENT The defoliating beetle (Cassida rubiginosus) WHAT DOES IT DO? See complete report for more information. AVAILABILITY http://www.mcclay-ecoscience.com/agents.htm for availability. _________________________________________________ BIOCONTROL AGENT The seed-head weevil (Larinus planus) WHAT DOES IT DO? See complete report for more information. AVAILABILITY http://www.mcclay-ecoscience.com/agents.htm for availability. _________________________________________________ BIOCONTROL AGENT The seed-head fly (Terellia ruficauda) WHAT DOES IT DO? See complete report for more information. AVAILABILITY http://www.mcclay-ecoscience.com/agents.htm for availability. _________________________________________________ BIOCONTROL AGENT The systemic rust fungus (Puccinia punctiformis) WHAT DOES IT DO? See complete report for more information. AVAILABILITY http://www.mcclay-ecoscience.com/agents.htm for availability. _________________________________________________ BIOCONTROL AGENT Small midge with yellow-orange larvae (Dasineura gibsoni) WHAT DOES IT DO? See complete report for more information. AVAILABILITY http://www.mcclay-ecoscience.com/agents.htm for availability. _________________________________________________ BIOCONTROL AGENT Painted lady butterfly (Vanessa cardui) WHAT DOES IT DO? See complete report for more information. AVAILABILITY http://www.mcclay-ecoscience.com/agents.htm for availability. _________________________________________________

Biopesticide Control

Currently none exist for this weed.

Herbicide Resistance

No documented cases of herbicide resistance to date. For more information on weed resistance: http://www.plant.uoguelph.ca/resistant-weeds/

Legislation

Noxious under the Ontario Weed Control Act.


Figure #1.

Canada thistle: A. Horizontal root with 2 aboveground shoots. B. Flowering stem.


Figure #2.

A young Canada thistle seedling.


Figure #3.

Canada thistle leaf.


Figure #4.

Canada thistle stems and alternate leaves.


Figure #5.

The root system of a Canada thistle seedling.


Figure #6.

Young Canada thistle plant, in field. Photo taken in spring, Southwestern Ontario.


Figure #7.

Canada thistles in flower.

Bio Control Agents

Click here to see complete report for more information.