The CSU Extension in Gilpin County helps mountain residents improve their quality of life by offering a website, classes and programs that provide unbiased, research-based information on forestry, wildfire, wildlife, mountain gardening, noxious weeds and many other issues. Through our 4-H programs, we help youth develop life skills and to become more interested in Science, Technology, Engineering and Math (STEM) learning.
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Canada Thistle   Arrow divider image - marks separation between nested pages that are listed as breadcrumbs.

Canada thistle (Cirsium (Breea) arvense)

Canada thistle Cirsium (Breea) arvense

Aggressive creeping perennial.

Reproduces by seed and also readily from roots. In Gilpin County, plants start going to seed in August.

It is difficult to control because its extensive root system allows it to recover from control attempts.

Combining control methods is the best form of Canada thistle management.

The key principle to Canada thistle control is to stress

 

the plant and force it to exhaust root nutrient stores.

Mowing or pulling alone is not effective unless conducted at one-month intervals over several growing seasons.Cirsium (Breea) arvense

If you do spray, do it in the fall after pulling or mowing once earlier in the season. Do not allow the plant to go to seed.

Glyphosate (Roundup) is fairly effective against Canada thistle, although repeat applications may be necessary. It is most effective when combined with cultural and/or mechanical control. Aminopyralid (Milestone) has been shown to be very effective.

Please note that there are some native thistles, which are not noxious plants.

Other Links For Further Information:

http://extension.colostate.edu/topic-areas/natural-resources/canada-thistle-3-108/

http://adams.colostate.edu/ag/canadathistle.htm

http://www.cwma.org/CanadaThistle.html

http://mtweed.org/weeds/canada-thistle/