Description:
Tansy ragwort is classified as a biennial herb. It can complete its life cycle as a winter annual and occasionally as a perennial, depending on environmental conditions. As a biennial, tansy ragwort spends the first year in the rosette stage, with petiolate (stalked) dark green, basal leaves. The leaf underside is somewhat hairy, and appears whitish. The overall rosette has a ruffled appearance, due to deeply indented and blunt toothed lobes of the leaves. The basal leaves are often deciduous. The size of the rosette may indicate the potential for flowering, with larger rosettes producing more flowers. During the second year, one or several flowering stems bolt, with the overall plant being one to four feet high. The leaves found on the flowering stem are alternate, and sessile. The flower heads are in flat topped clusters. Each flower head is composed of yellow, daisy-like flowers. Each flower head is a composite of many disc flowers surrounded by (usually) 13 ray flowers. A distinguishing characteristic is the 13 ‘petals’, which are ray flowers. Tansy ragwort has a taproot, and often a large woody rootstock. Initial infestation is by seed.

• Mechanical: Hand pulling is effective on small infestation sites of tansy ragwort. Pulling when the soil is moist will help to remove the whole root, as tansy ragwort will resprout from root fragments. Covering the site with mulch will help prevent new germination from the disturbed site. (Sweeney et al. 1992).
• Biological: In its native habitat, tansy ragwort is controlled by over 60 species of natural enemies that feed on this species. (Cameron 1935 as cited in Sweeney et al. 1992). Three natural enemies of tansy ragwort were introduced in California between 1959 and 1966. The ragwort flea beetle (Longitarsus jacobaeae), the ragwort seed fly (Pegohylemyia seneciella), and the cinnabar moth (Tyria jacobaeae) are the biological agents effectively used to control tansy ragwort in Oregon, California, and Washington. The cinnabar moth and the ragwort flea beetle are unable to establish east of the Cascade Mountains (Rees et al. 1996).l
• Herbicide: Chemical control is effective against tansy ragwort. 2,4-D is effective when applied to rosettes in the spring, or applied to the new growth initiated after fall rains. Dicamba is effective on plants with large rosettes or flowering stalks. Tordon controls scattered populations. Glyphosate is also used for effective control (Sweeney et al. 1992).

For More Information:
Detailed information about Tansy Ragwort is available at the Washington State Noxious Weed Control Board Web Site.