Scotch thistle (Onopordum acanthium)

Scotch thistle

(Onopordum acanthium)

Description

    • Biennial or perennial member of the Asteraceae family.
    • Can grow over two metres in height.
    • Branched, wooly stems with spiny wings.
    • Large purple flower heads.
    • Tolerates a variety of soils, prefers moist soils.
    • Compared to bull thistle, scotch thistle has larger flowerheads and leaves that are woolly, while bull thistle leaves are mostly smooth.
    • Very limited distribution, single sites in Nelson, Castlegar, Rossland and Slocan valley.

Consequences of invasion

  • May be competitive with native vegetation in rangelands.
  • Forms dense stands that are impenetrable to livestock and impact recreational sites and trails.

Introduction and spread

  • Native to Europe.
  • Seeds can be transported by wind as well as attaching to clothing, animal fur and machinery.

Management Options

  • Prevent the spread of this plant by following CKISS tips.
  • Monitor at-risk areas (moist and/or disturbed sites) regularly to identify this plant while infestations are still manageable.
  • Pull or dig small infestations when soil is moist and before seeds have set.
  • Cut a few inches below the soil surface.
  • Mow or slash before seedset. Plants can reproduct from fragments, so monitoring and hand-cutting/pulling is still required after mowing.
  • Chemical control may be appropriate for larger infestations.
  • Establish perennial grasses or other appropriate plants and monitor their success over time.

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