Why Is It a Noxious Weed?
Tansy ragwort is toxic and a threat to livestock and agriculture. All plant parts are toxic, with the highest amount of alkaloids in flowers then leaves, roots and stems. Toxic properties are a possible threat to humans through food chain contaminants. Find out more about tansy ragwort toxicity in our booklet: Protect Your Horses and Livestock From Toxic Plants.
How would I identify it?
It is a biennial to sometimes annual or perennial herbaceous plant. As a biennial, tansy ragwort spends the first year in the rosette stage with dark green basal leaves that appear ruffled. During the second year, one or two flowering stems form.
Flowerheads are in flat topped clusters. Flowerheads yellow with many disk flowers and 13 ray flowers, overall flowerhead daisy-like in appearance. Flower heads have around 13 bracts at their base with dark tips.
Leaves are twice divided, with petioles on leaves near the base and without petioles toward stem tips. First year leaves in a basal clump (rosette). Second year leaves are alternate along the stem, 1.6 to 7.9 inches long by 0.8 to 2.4 inches wide.
Stems reach up to 4 feet tall, numbering one to many from roots. They branch near their tips.
Fruit Seed Description
Seeds are sparsely hairy to glabrous (hairless and smooth).
May Be Confused With
Common St. Johnswort (Hypericum perforatum) and common tansy (Tanecetum vulgare), Class C noxious weeds, may be mistaken for tansy ragwort. Common St. Johnswort flowers have 5 petals per flower (tansy ragwort commonly has 13 'petals') and common tansy does not have any petals (ray flowers). Click here to see a comparison of the flowers of these species. If you need help with plant identification, contact your county noxious weed coordinator.
Where does it grow?
Tansy ragwort is found on roadsides, in pastures, fields and cleared forested areas. It is not particular to soil type. Please click here to see a county level distribution map of tansy ragwort in Washington.
How Does it Reproduce?
Tansy ragwort usually reproduces by seed, although it can also reproduce vegetatively.
How Do I Control It?
After tansy ragwort control, plant areas with site appropriate plants to provide competition and reduce further invasion. Monitor areas for seedlings and resprouts.
Small infestations can be controlled manually by pulling up the entire plant, including its roots. Wear protective gloves when pulling and handling plants. If you pull flowering plants, seal them in a plastic bag and put them in the trash—not in your compost or yard waste. Pull plants while the soil is still moist, roots will come out more easily. Roots left in the ground may resprout so remove as much as possible and continue to monitor the area. Plants are easier to find when they are beginning to form their flowering stems, but if you can pull the plants as rosettes, you will have less plant material to dispose of. Large infestations are better handled by a combination of manual and chemical controls. Mowing alone is not effective as tansy ragwort can re-sprout if entire plant is not removed, behaving as a perennial until the plant is removed. Mowing can be used as an interim measure to keep it from blooming and going to seed, but other control methods will be needed the same year before flowers form.
Good pasture management techniques will help to prevent or reduce infestations. Seed and/or plant areas with non-invasive plants to provide competition and suppress seed germination of tansy ragwort.
The tansy ragwort flea beetle, Longitarsus jacobaeae, larvae and adults are destructive to tansy ragwort. Larvae feed on and within the roots and the adults feed on leaves. The ragwort seedhead fly, Botanophila seneciella, larvae feed within seedheads, often destroying all of the developing seeds. The cinnabar moth, Tyria jacobaeae, caterpillars can completely defoliate tansy ragwort. Unfortunately the cinnabar moth can also feed on native and horticultural species of Senecio and Packera so further redistribution of the moth is discouraged in many areas. If you have questions or are looking for more information about these biological control agents of tansy ragwort, please visit WSU Extension Integrated Weed Control Project.
For More Information
See our brochure Tansy Ragwort, A Toxic, Noxious Weed in Washington for more information on tansy ragwort.
See our Written Findings for more information about tansy ragwort (Senecio jacobaea).
See our press release on tansy ragwort from August 2011.
Clallam County NWCB Fact Sheet on tansy ragwort
Pierce County NWCB Fact Sheet on tansy ragwort
Mason County NWCB Fact Sheet on tansy ragwort
Jefferson County NWCB Fact Sheet on tansy ragwort
Island County NWCB Fact Sheet on tansy ragwort
Stevens County NWCB Fact Sheet on tansy ragwort
King County NWCB Fact Sheet on tansy ragwort
King County NWCB Fact Sheet on tansy ragwort in Spanish
Clark County NWCB Fact Sheet on tansy ragwort
Cowlitz County NWCB Fact Sheet on tansy ragwort
Whatcom County NWCB Fact Sheet on tansy ragwort
Thurston County NWCB Fact Sheet on tansy ragwort
San Juan County NWCB Brochure on tansy ragwort
Control Options for tansy ragwort from Whatcom County NWCB
Control Options for tansy ragwort from King County NWCB