Canada thistle (23887 bytes)

Canada Thistle: Cirsium arvense

Canada Thistle is a creeping perennial.The foliage is spiney.

It is considered to be a noxious weed which is difficult to eradicate because of its extensive root system. When mowed in a lawn, it will not develop full height and flower. Canada thistle is invasive due to shoots from its root system. Pulling generally is not effective due to the tremendous reserves in the root system, and new shoots appear soon after pulling. Regular, persistent pulling may gradually starve the root system. Shoots should be pulled as they are noticed, since all shoots (leaves) are producing food reserves.

thistle blossoms (12341 bytes)

Thistle blossoms

          Thistle seedheads (7040 bytes)

Thistle seedheads

Turf density and competetiveness can be increased with the proper cultural practices described in CSU Fact Sheet 7.202, Lawn care.

Control

Herbicides such as glyphosate can be painted on thistle leaves. Repeat applications will be needed. Herbicides such as triclopyr + clopyralid or 2,4-D combinations can be sprayed on thistle foliage; repeat applications may be needed at 6 week intervals. The most effective times for herbicide applications are spring, just after the green shoots appear, or in August/September. Always read the label before applying any pesticide.

Photographs courtesy of Judy Sedbrook.

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Date last revised: 01/05/2010