Tansy Ragwort

Tansy Ragwort

Scientific name: Senecio jacobaea

Common names: Tansy ragwort

Description: Tansy ragwort is a tap-rooted biennial (sometimes perennial) that can grow up to 4 feet tall. It was introduced from Europe in the early 20th century and can spread in contaminated hay. In its first year, it puts out a rosette of dark green ruffled or lobed leaves, and in the second year displays conspicuous daisy-like yellow flower heads. The plant typically sets seed in August, with individual plants producing up to 150,000 seeds.

Impact: Tansy ragwort is prolific in disturbed areas and pastures, where they can establish extremely dense populations. In the 1960′s and 70′s, it caused significant economic damage to livestock owners in Oregon due to its toxicity and the inability of livestock to detect/avoid dried leaves mixed in with other silage. Efforts to biologically control tansy ragwort in Oregon have resulted in a reduction of impact “below economic threshold levels”. However, it is still considered widespread throughout the region and due to its ability to retain seed viability for 15 years, it is difficult to eradicate from sites.

Sources: KingCounty.gov, oregon.gov

For more information, please visit the Noxious Weed resources at KingCounty.gov: http://www.kingcounty.gov/services/environment/animals-and-plants/noxious-weeds/weed-identification/tansy-ragwort.aspx