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Invasive Species in Amherst State Park

Cirsium arvense - Canada Thistle, Creeping Thistle

Close up Photo

photo by  WNY PRISM

June 5, 2015

Infestation Photo

photo by  WNY PRISM

June 5, 2015

Hesperis matronalis - Dane’s Rocket

Close up Photo

photo by  WNY PRISM

June 5, 2015

photo by  WNY PRISM

June 5, 2015

Infestation Photo

photo by  WNY PRISM

June 5, 2015

    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.

    Dame’s rocket (Hesperis matrolalis) is a biennial herb from the mustard family native to Eurasia. It was introduced to North America in the 1600’s to become invasive in moist wooded areas and open areas. Garden centers may sell Dame’s rocket as a short lived perennial and in “Wildflower” seed mixes. An erect plant with fragrant, purple, pink, or white flowers which bloom from April through August. The plant’s ability to bloom for many months with abundant seeds has caused its widespread distribution.  

    Dame’s rocket lacks natural predators and diseases in North America and so it competes with native species for water, light and nutrients, often forming dense monocultures. It competes with native plants at the edges of woodlands, in woodland openings, and in semi-open forests. This competition for resources inhibits tree seedling germination and growth.