Tansy ragwort
Senicio jacoaea L.
Keys to Identification
Multiple yellow flowers in inflorescence.
- Stems may be purplish-red.
- Disk flowers have black tips.
Family: Asteraceae (Sunflower)
Other Names: Stinking Willie, tansy butterweed
USDA Code: SEJA
Legal Status: Colorado Noxious Weed List A
Identification
Lifecycle: Biennial or short-lived perennial
Growth form: Forb
Flower: Yellow. July-September. Has both ray and disk flowers.
Seeds/Fruit: Disk flowers are hairy. Ray flowers are smooth
Leaves: 2-8 inches long. Multi-lobed
Stems: Mature plants range from 1-6 feet in height. Stems have downy hairs.
Roots: Taproot with fleshy side roots
Similar Species
Exotics: None known.
Natives: Senicio sp., Grounsel
Impacts
Agricultural: Toxic to livestock
Ecological: Displaces native vegetation
Habitat and Distribution
General requirements: Found in pastures, along rights-of- way and disturbed places. Prefers moist soils
Distribution: Found in California, Idaho, Illinois, Maine, Massachusetts, Michigan, Montana, New Jersey, New York, Oregon, Pennsylvania, Washington. Recently found in Alaska. Not known to occur in Colorado.
Historical: Tansy ragwort is native to Europe. Known in North America since the early 1900's.
Biology/Ecology
Life cycle: Tansy ragwort generally produces a basal rosette the first year, and flowers the following year. The plants are prolific bloomers and produce large quantities of seed from July through September.
Mode of reproduction: Reproduces by seeds. May sprout from root fragments.
Seed production: Produces up to 150,000 seeds.
Seed bank: The majority of the seeds will germinate the following year, but some seeds may remain dormant for several years.
Dispersal: Wind
Integrated Management Summary
As with other plants which reproduce primarily by seed, integrated management efforts must include the elimination of seed production and the depletion of the seed bank. Combine herbicide or mechanical removal of rosettes with removal of seed heads from any plants that have bolted. Apply herbicides at rosette to early bolt stages.
References
Whitson, T.D.(ed.), L.C. Burrill, S.A. Dewey, D.W. Cudney, B.E. Nelson, R.D. Lee, R. Parker. 2001. Weeds of the West. Western Society of Weed Science, in cooperation with the Western United States Land Grant Universities Cooperative Extension Services, Newark CA.
Growers Weed Identification Handbook, University of California Publication 4030, pg. WI-212
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