Introduced Pests Outreach Project

Tansy Ragwort

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Scientific Name: Senecio jacobaea
Common Names: Tansy ragwort, Stinking Willie, Tansy Butterweed

Full sun or partial shade in pastures and fields, along roadsides, and in open disturbed areas. (Figure 1)
Tansy ragwort will tolerate a wide variety of soil types.

Key ID Features
Herbaceous, biennial or short-lived perennial that reaches 8 in. to 3 ft. in height (Figures 2 and 3)
In the first year a basal rosette of lobed leaves with a ruffled appearance is produced. Leaves range from 1.5-8 inches long and 0.75 to 2.25 inches wide (Figure 4)
Stems branch near the top to bear numerous, yellow, daisy-like flowerheads. Tansy ragwort flowers from July through October (Figure 5)
Each flower is composed of a central cluster of disc flowers surrounded by 10 to 15 ray flowers. (Figure 6)
Fruits are light brown in color and very small (0.08 inch). Some seeds have a pappus (tuft of fluff like a dandelion seed) that aids in dispersion by wind. (Figure 7)
This plant contains pyrrolizidine alkaloids which are toxic to cattle and horses.

Similar species:

Golden ragwort (Senecio aureus)
Leaves are cordate (heart-shaped). (Figure 8)
Leaves on the stem are greatly reduced compared to tansy ragwort.

Fact sheets and references:
Tansy Ragwort Identification: King County, Washington Noxious Weed Control Program

Best Management Practices Tansy Ragwort: King County, Washington Noxious Weed Control Program

Tansy Ragwort Weed Alert

Senecio jacobaea- Invasive Plant Atlas of New England: Description and great photos, history of the plant in New England, and similar species

Information on toxicity of tansy ragwort to livestock: USDA, ARS Poisonous Plants Research Lab

Tansy ragwort: Washington State Noxious Weed Control Board

Field Guide to Noxious and Other Selected Weeds of British Columbia

Tansy ragwort pictures, distribution maps, and additional resources: Forestry Images.

last reviewed December 22, 2014

Massachusetts Department of Agricultural Resources
The Massachusetts Introduced Pests Outreach Project is maintained by staff at the Massachusetts Dept. of Agricultural Resources. This website was made possible, in part, by a Cooperative Agreement from the United States Department of Agriculture's Animal and Plant Health Inspection Service (USDA APHIS). It may not necessarily express APHIS' views.