Tansy Ragwort

Senecio jacobaea

   

Family: Asteraceae

Weed Class: B

Year Listed: 1988

Native to: Northern Africa, Asia and Europe

Toxic: humans, livestock

additional photos

 

   

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.

How would I identify it?

General Description: It is a biennial and sometimes a perennial herb. 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 emerge.

Flower Description: 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.

Leaf Description: 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.

Stem Description: 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). If you need help with plant identification, contact your county noxious weed coordinator.

How does it reproduce?

Tansy ragwort usually reproduces by seed, although it can also reproduce vegetatively.
 

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 do I control it?

General Control Strategy

Small infestations can be controlled manually by pulling up the entire plant, as long as it is done before flowers begin to seed. Pulled plants that have flowers should be bagged prior to throwing away. Large infestations are better handled by a combination of manual and chemical controls.

Mechanical Control

Mowing is not effective, and tansy ragwort can re-sprout if entire plant is not removed. Tansy ragwort becomes a perennial, and will re-grow every year until the plant is removed.

Cultural Control

Good pasture management techniques will prevent infestations.

Biological Control

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.

Herbicide Control

Please refer to the PNW Weed Management Handbook, or contact your county noxious weed coordinator.


 

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.

Additional Photos


 
 

Tansy ragwort flowers

Tansy ragwort basal leaves

Young tansy ragwort plant

Tansy ragwort plant in flower

in seed

in bloom and beginning to develop seeds

infestation in bloom and going to seed

flowerheads in bloom

example of stem leaves

    

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