CWMA

PO Box 419

Hotchkiss, CO 81419

 

970-361-8262

fax: 720-880-3051


Email:contact@cwma.org

 

 

Tansy ragwort

Senicio jacoaea L.

 

Keys to Identification

  • Multiple yellow flowers in inflorescence.
  • Stems may be purplish-red.
  • Disk flowers have black tips.

Family: Sunflower (Asteraceae)

 

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 in long. Multi-lobed

 

Stems: Mature plants 1-6 ft tall. 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: Seed. 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

 

 

 

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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