Description:

Tansy ragwort is a tall biennial plant in the sunflower family. It can grow up to 6 feet in height at maturity. The rigid stems of Tansy ragwort are green with an occasional reddish tinge. Plants typically arise from a single stem that becomes branched at the top of the plant, forming flat clusters of bright yellow flowers. The yellow daisy-like flowers have dark yellow to orange centers. Leaves are dark green and ruffled in appearance. Tansy ragwort grows as a rosette in its first year before transitioning into the mature flowering form in its second year of growth. Tansy ragwort can form dense patches, particularly on disturbed sites. This noxious weed is dangerous to humans and livestock due to a poisonous alkaloid (hepatotoxic pyrrolizidine) in its tissue which causes liver damage when ingested.

Life cycle:

Perennial

Height of mature plants

3-6 feet

Flower color:

Yellow

Bloom time:

July to September

Look-a-likes:

From a distance, tansy ragwort can look like common St. John’s wort (Hypericum perforatum), but upon looking more closely, tansy ragwort has large ruffled leaves, whereas St. John’s wort has many small leaves. Also, tansy ragwort has flowerheads with 13 petals, while St. John’s wort has 5.

Habitat:

Tansy ragwort is opportunistic plant often found in disturbed areas. Tansy likes a cool and wet climate, well drained soils and full to partial sun. Patches are found in pastures, fields, grasslands, vacant land, waste places, horse trails, roadsides, rangeland, riparian areas, forested areas, and clear cuts. Areas of greatest concern are improperly managed pastures and disturbed areas.

Impacts:

Prolific in pastures, clear cuts, and disturbed roadside areas, tansy populations can become quite dense. The leaves are toxic to cattle and horses, causing irreversible liver damage. In the 1960’s and 70’s livestock losses in Oregon amounted to 5 million dollars a year. Unlike cattle and horses, sheep appear to be unaffected by ragwort’s toxicity. Once considered Western Oregon’s most economically serious noxious weed, biological controls have reduced the severity of outbreaks below economic threshold levels.

Noxious Weed Listing:

• WeedWise: Maintenance
• State of Oregon: Class B
• State of Washington: Class B
• Four County CWMA: Class C

Origin:

Eurasia

Links:

Oregon Noxious Weed Profile
Washington Noxious Weed Profile
Invasive.org profile
CABI Invasive Species Compendium