Ecology and Management of Tansy Ragwort (Senecio jacobaea L.)

Invasive Species Technical Note Number MT-24

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Invasive Species Technical Note Number MT-24 (PDF; 204 KB)

By Jim Jacobs, Plant Materials Specialist, NRCS, Bozeman, Montana
Sharlene Sing, Research Entomologist United States Forest Service (USFS) Rocky Mountain Research Station, Bozeman, Montana

Abstract

Tansy ragwort, a member of the Asteraceae taxonomic family, is a large biennial or short-lived perennial herb native to and widespread throughout Europe and Asia. Stems can grow to a height of 5.5 feet (1.75 meters), with the lower half simple and the upper half many-branched at the inflorescence. Reproductive stems produce up to 2,500 bright golden-yellow flowers. Capitula (flowerheads) arranged in 20-60 flat-topped, dense corymbs per plant are composed of ray and disc florets; both produce achenes containing a single seed. Rosettes formed of distinctive pinnately-lobed leaves attain a diameter of up to 1.5 feet (0.5 meter). First reported in Montana in 1979 in Mineral County, tansy ragwort has since spread into Flathead, Lincoln, and Sanders Counties. Soils with medium to light textures in areas receiving sufficient rainfall (34 inches or 860 millimeters/year) readily support populations of tansy ragwort. This species is a troublesome weed in decadent pastures, waste areas, clear-cuts and along roadsides. Tansy ragwort produces pyrrolizidine alkaloids - these can be lethal if ingested by cattle, horses and deer, but are less toxic to sheep and goats. Unchecked infestations can result in significant livestock losses, decreased pasture yields and increased management costs (see Figure 1).

Figure 1. A tansy ragwort infested pasture. Photo by Eric Coombs, Oregon Department of Agriculture, available from Bugwood.org

Auxinic herbicides such as 2,4-D and picloram can provide effective control of tansy ragwort when applied to actively growing immature plants in the spring or fall. Grazing should be deferred at least three to four weeks after herbicide application to prevent livestock poisoning because spraying increases tansy ragwort’s palatability. The tansy ragwort flea beetle (Longitarsus jacobaeae) and the cinnabar moth (Tyria jacobaeae) reportedly provide regional biological control of tansy ragwort. Mowing is ineffective in controlling tansy ragwort because it stimulates vegetative growth and leaves below-ground roots intact. Prescribed burning during the reproductive stage may reduce populations. Grazing management and nutrient management promoting dense and continuous turf are important for control and prevention because tansy seedlings cannot establish on closed vegetation sites.

Plant Biology

• Identification
• Life History
• Habitat, Spread and Impacts

Management Alternatives

• Chemical, Mechanical and Cultural Control
• Biological Control

References

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Last Modified: 11/10/2011