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Invasive Species in Amherst State Park

Cirsium arvense - Canada Thistle, Creeping Thistle

    Canada thistle (Cirsium arvense) is a perennial, rhizomatous herb native to Europe and Asia. It grows 2 to 5 feet tall. Leaves have spiny crinkled edges and stems branch at the top with numerous fragrant, pale magenta lavender, or white, rayless flowers. It flowers in the months of June through October. Once established, Canada thistle spreads quickly replacing native plants. It grows in circular patches, spreading through roots which can expand up to 10-12’ in one season. Canada thistle produces an extensive, rhizomatous root system, which may extend 20 feet below ground.

    Repeated mowing and cutting the Canada thistle at the base of the stem for several years may suppress the plant, but their substantial root system allows it to recover from damage. Therefore, cutting or mowing must be done several times a year, in order to stress the plant enough to prevent it from spreading. It is impossible to pull up all of the root of Canada thistle, and broken rhizomes only encourage the plant to produce more sprouts. Because of this, hand pulling is not a viable treatment option. Herbicide treatment combined with mowing is the most effective treatment.