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5/5/08 | Honey bees
Canada thistle (Cirsium arvense) is considered a noxious weed in Missouri, which means landowners are required to control it.
Canada thistle is a perennial plant that originated in Europe
and came to the United States in contaminated crop seed.
Unlike other thistles, which are biennials, Canada thistle is a rhizomatous, colony-forming perennial. It also reproduces by seed that can be blown great distances. The leaves are alternate, lack petioles, are irregularly lobed and have spines along the margins. The upper leaf surface has a waxy appearance and lacks hair. A key feature of Canada thistle is the base of the leaf, which clasps completely around the stem. Flower heads are produced in clusters and may range in color from pink to purple, and occasionally, white.
Canada thistle occurs in reduced-tillage cropland and in rights-of-way, fencerows and industrial sites. Several products can be used to control the thistle, including 2,4-D, dicamba (Banvel/Clarity, Distinct), Stinger, Hornet and glyphosate. Not all products can be used in all crops or growing conditions. The most effective timing for control is when thistles are in the early bud stage in the spring, or in the fall before a killing frost.
Updated 1/17/08