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
Massachusetts Introduced Pests Outreach Project is a collaboration between the Massachusetts Dept. of Agricultural Resources and the UMass Extension Agriculture and Landscape Program. 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 (APHIS). It may not necessarily express APHIS' views.