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Pacific Northwest Research Station
Blue Mountains National Resources Institute

Forestry and Range Sciences Laboratory
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BMNRI Home > Publications > Weeds > Scotch Thistle

Publications: Noxious Weeds

Explosion in Slow Motion: A talk by Jerry Asher about noxious weeds in the Blue Mountains

Click on a weed to learn about how to find it and kill it!

Common Crupina
Diffuse Knapweed
Russian Knapweed
Spotted Knapweed
Purple Loosestrife
Perennial Pepperweed
Tansy Ragwort
Medusahead Rye
Rush Skeletonweed
Yellow Starthistle
Canada Thistle
Musk Thistle
Scotch Thistle
Dalmatian Toadflax
Mediterranean Sage
St. Johnswort
Leafy Spurge
Dyers Woad

Wanted: DEAD!

Scotch Thistle

Alias: Cotton thistle

  • Stems: Broad spiny wings. Grows up to 8 feet tall.
  • Leaves: Alternate, irregularly lobed and toothed, the margins bearing sharp yellow spines. Occasionally 2 feet long, but usually smaller.
  • Flowers: Globeshaped, upright, spiny, 2 inches across and purple. Flowering heads are numerous, 1 to 2 inches in diameter, bracts all spine tipped.
  • Seeds: Smooth and slender, and tipped by a cluster of slender bristles; contained in 3/16-inch long, wrinkled fruit.

Scotch thistle is a spiny biennial. The whole plant appears hairy or woolly. It usually occurs along roadsides, in waste areas, and on rangelands along stream courses, lower slopes, and bottomland where moisture occurs. It often forms dense stands impenetrable to livestock.

Control: Call your local weed board, agriculture extension office, or other land management agency for information on current control methods.

Report all sightings to your local Weed Board

US Forest Service - Pacific Northwest Research Station, Blue Mountains National Resources Institute
Last Modified: Monday, 16 December 2013 at 14:18:43 CST

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