USDA Forest Service

Blue Mountains National Resources Institute

Education Links
Information Providers
Managing Disturbance Regimes
Pacific Northwest Research Station
USFS Research & Development
Evaluate Our Service
Your comments and suggestions are very important to our service improvement.

Pacific Northwest Research Station
Blue Mountains National Resources Institute

Forestry and Range Sciences Laboratory
1401 Gekeler Lane
La Grande, OR 97850

United States Forest Service.

BMNRI Home > Publications > Weeds > Tansy Ragwort

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!

Tansy Ragwort

  • Stems: 1 to 6 feet tall, thinly covered by cobwebby hairs; many branches near the top.
  • Leaves: Divided into lobed and toothed segments, the terminal lobe generally larger than the lateral. Stem leaves are dark green, and ruffled, with blunt tips. First year plant is a rosette with leaves up to 9 inches long.
  • Flowers: Numerous heads. Flowers are yellow, 1-inch-wide, and daisy-like. Flowering season in July through September.
  • Seeds: Tiny, tipped with hair-like plumes that carry them on the wind for long distances.

Every part of the Tansy Ragwort plant is poisonous; it causes liver damage in horses and cattle. It spreads by seed; each plant can produce 150,000 seeds that remain viable for 15 years.


  • Biological: The cinnabar moth larvae feed on the leaves, buds, and flowers; the ragwort seed fly larvae feed on the developing seed; and the tansy ragwort flea beetle larvae feed on the roots of the plant, and the adults feed on the leaves. These insects complement each other. Introduction of competitive native vegetation is also a good idea.
  • Chemical: Certain herbicides readily kill tansy ragwort seedlings. They are most effective before stem elongation. Tansy ragwort dies slowly after herbicide application, and treated plants are still poisonous 4 to 6 weeks after spraying.
  • Mechanical: Cutting or mowing is only recommended when other eradication methods are planned. Cutting does not kill the plant, although if done before the early flowering period it will reduce seed production. Pulling is worthwhile if the infestation is very small, it is repeated consistently, and is followed up with herbicide application. A thorough plowing each year can kill most plants, and eventually deplete the seed stock.

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

USDA logo which links to the department's national site. Forest Service logo which links to the agency's national site.