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Weed ID: Canada Thistle (Cirsium arvense)

CanadaThistle_llCanada thistle is a perennial herb that grows 3-4 ft in height with a very extensive creeping root system. Although its name would lead you to believe otherwise, Canada thistle is actually native to Europe and Asia and is thought to be accidentally introduced to North America in the 1600’s. It can be easily identified by its prickly and hairy leaves as well as its purple or white flowers. This invasive weed grows on a wide variety of soil types and is common in pastures, roadsides, open forest land, abandoned fields, and even wet meadows. Canada thistle spreads by seeds and an extensive root system that can have runners 5-15ft deep and 15 feet horizontally. Winning the war on a Canada thistle infestation requires some persistence from the land manager and often takes 2-3years. This aggressive growing plant can be controlled with a variety of herbicides, depending on the crop or habitat it is growing in. The key to beating it is to stress the plant enough to use its nutrient stores in its root system. Herbicide treatments in the spring and early fall before plants mature and produce seed prove to provide good control. Mowing can be somewhat effective in controlling Canada thistle, but only when done monthly for several growing seasons to stress the plants. An herbicide treatment plan with mechanical removal including tilling and mowing is most effective.


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