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.

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.

Status in the CKISS region

  • Scotch thistle is classified as Eradicate/Annual Control on the CKISS Annual Priority List.
  • This plant is present on a few sites in the Creston, Lower Arrow and Slocan Valley Invasive Plant Management Areas.
  • To learn more about how CKISS classifies and manages invasive species, see our Invasive Species Priority Lists page.

Integrated pest management options

  • Prevent the spread of this plant by following CKISS tips.
  • Be PlantWise and avoid introducing scotch thistle to your garden.
  • 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 seed set. Plants can reproduce 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.

Additional resources