Common tansy

(Tanacetum vulgare)

A native of Europe imported as an ornamental and for medicinal purposes, this perennial plant reproduces by seed and by rootstock. At maturity the plant can grow between 2 and 6 feet tall with 1/4″ to 1/2″ diameter yellow button-like flowers at the top. Leaves are deeply divided into narrow toothed segments. Stems are reddish-purple and emit a strong odor when crushed. It is commonly found along irrigation ditches and streambanks and is therefore very difficult to control.

The plant is considered toxic and care should be taken when handling the vegetation during control efforts. Common tansy has been found along irrigation ditch banks throughout the Roaring Fork Valley. There have also been isolated patches along Elk Creek west of New Castle, as well as along the Colorado River south of Silt.