DESCRIPTION: Common Tansy is a member of the Composite (aster) family also known as (Chrysanthemum vulgare). The plant grows two to five feet tall with yellow, button-like flower clusters. The exotic should not be confused with the native, rare eastern or Lake Huron tansy (Tanacetum huronense), which only grows sixteen to thirty-two inches high and has fewer larger flowers.
Where present, Common Tansy is highly visible and common to roadsides, pastures, fields, prairies and hedgerows. It grows in sunny, well-drained soils and blooms July to October. Its leaves are pinnately compound and alternate, with deeply divided, toothed fernlike leaflets. Several smooth or slightly hairy erect stems arise from each base, which are woody and purplish red near the ground. The plant emits a strong fragrance when crushed.
DISTRIBUTION AND HABITAT: Common Tansy, also known as Bitter Buttons, Cow Bitter, Mugwort or Golden Buttons, is a perennial native to temperate Europe and Asia. The plant was brought to the U.S. in the 1600’s for horticultural and medicinal purposes. It was used to treat external and internal parasites. Heavy consumption could be dangerous because the plant’s volatile oil contains thujone, a substance that can cause convulsions and miscarriages. The plant is used in dried flower arrangements and unfortunately is still being sold commercially as an ornamental for its very showy, yellow flower. It frequently escapes cultivation and can be problematic when trying to restore previously disturbed sites to native vegetation.
LIFE HISTORY AND EFFECTS OF INVASION: This perennial plant spreads via an extensive, spreading root system and profuse seed production. It especially favors disturbed soils along ditch banks, where the water quickly spreads the seeds for miles. Common Tansy is now widespread from coast-to-coast, across most northern states and Canadian provinces.
Mechanical Controls: Literature is conflicting when discussing the effectiveness of pulling, cutting or mowing. It is agreed that if done prior to seeding, it will reduce seed production, but there is disagreement on whether this method has an overall controlling affect. Tansy regenerates from root fragments, so cultivation could expand the size of an infestation.
Chemical Controls: Picloram (Pathway), dicamba (Banvel, Veteran CST) and gyphosate (Round-up) are herbicides that can be effective on tansy when applied properly. For a complete list of trade names, please consult a certified pesticide dispenser. A combination of mechanical and chemical methods seems to have the best results. Patches must be monitored annually to remove plants that regenerate from the roots.
Fire: Dense patches of dried tansy stalks burn very hot and fast, but it is unclear if this is a reliable control method.