Link to the WSNWCB Home Page link to the About Us page Link to the Weed Laws page Link to the Noxious Weed List Link to the Weed Information page link to the Frequently Asked Questions page Link to the Education page Connect to other Links page Link to Contact Us page

Class B Noxious Weed

Scotch Thistle
Onopordum acanthium
 

Scotch thistle flower


Plant family: Asteraceae (Compositae)
Year listed:
Native to: Europe and Asia

Why is it a noxious weed?
Scotch thistle is a problem in rangeland. Infestations of Scotch thistle reduce forage production and virtually prohibit land utilization for livestock. Dense stands of the large, spiny plants make livestock movement extremely difficult, almost totally excluding animals from grazing and access to water.

 

How would I identify it?
General Description: Scotch thistle is a branched, biennial or annual can grow up to 8 feet or more in height and 6 feet in width.

Leaves:

  • covered with sharp yellow spines
  • up to 2 feet long, 1 foot wide
  • upper and lower leaves are covered with a thick mat of cotton-like or woolly hairs
  • hairs give foliage a gray-green appearance

Flowers:

  • globe shaped
  • groups of 2 or 3 flowers on branch tips
  • dark ping to lavender

Stems:

  • have vertical rows of prominent, spiny "wings"

How does it reproduce?
Scotch thistle reproduces by seed. Each plant can produce 8,400 to 40,000 seeds .

Where does it grow?
Scotch thistle will grow in wet meadows and pastures as well as dry pastures and rangelands. It may also be found alongside streams and rivers.

What is the distribution in Washington State?

Click on map to enlarge.
  • Scotch thistle has been documented in several counties, with the majority of the infestations being on the Eastern side of the State.
  • Distribution map is based on 2003 data.

How do I control it?

General control methods: Establishing a dense well-maintained pasture is effective in preventing a Scotch thistle infestation.

Cultural: Goats will graze Scotch thistle, preventing seed production.

Herbicide:  Please refer to the PNW Weed Management Handbook, or contact your county noxious weed coordinator.

Mechanical: Small areas can be dug out. Mowing has limited effectiveness for controlling Scotch thistle, usually only prevents seed production.

Biological: None known.

For more information
For more information, download our Written Findings.

View the Garden Wise Eastern Washington and Western Washington Guides for better noninvasive plant recommendations for your yard or garden.

More Photos-Click photo to enlarge
Feel free to download, or contact us to receive high-resolution JPEG or TIFF formats
Scotch thistle plant. Scotch thistle infestation.

 Last updated September 10, 2008