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A banner year for tansy ragwort

  • Written by Wendy DesCamp, Washington State Noxious Weed Control Board
Tansy flowering
Second year plants will grow one or more leafy stems up to 4 feet tall and develop flat-topped clusters of yellow flowerheads. Each daisy-like flowerhead generally has 13 petals.
Phones are ringing off the hook at county weed board offices as people call in to report sightings of tansy ragwort (Senecio jacobaea), which is primarily blooming in Western Washington and in some cases starting to set seed.This toxic Class B noxious weed in Washington state is thriving due to the cooler weather in the Pacific Northwest this year, much to the dismay of farmers and horse owners.

Tansy ragwort is a tap-rooted biennial or short-lived perennial plant that is native to Eurasia. For the first year, young plants form a rosette of coarse, ruffled leaves with red stems. Second year plants will grow one or more leafy stems up to 4 feet tall and develop flat-topped clusters of yellow flowerheads. Each daisy-like flowerhead generally has 13 petals. Plants spread by seed which can be dispersed by the wind, animals and people. Disturbance, such as mowing, may cause the plant to behave as a perennial, appearing year after year.

Tansy ragwort often grows where land has been disturbed and where grass and other plants are sparse. It is commonly found on roadsides, in heavily grazed pastures, fields and cleared forested areas.

Due to its toxicity and invasiveness, tansy ragwort is a listed Class B noxious weed in Washington. It is designated for control in many counties throughout the state, which means that landowners in these counties are required by law to control and prevent the spread of this noxious weed. Control of this plant is encouraged by everyone and is especially appreciated by farmers since it can be lethal to cattle and horses and, and to a lesser extent goats (and seldom sheep).

Tansy ragwort contains pyrrolizidine alkaloids that are toxic and can slowly accumulate and cause liver damage in livestock. Due to these toxins, it should never be used as an herbal remedy or tea. It can also have other economic impacts by contaminating hay fields and tainting milk and honey.

Proper removal and control of tansy ragwort is important to reduce and prevent infestations. Small patches can be hand pulled, making sure to remove the roots, which can resprout. It is best to pull plants before they begin to flower. Pulling rosettes in the fall is a great way to reduce next year’s flowering stems and also avoid accidental grazing by animals. Plants have viable seed as soon as they begin to flower, so pull and bag flowering plants and put them in the trash — not in your compost or yard waste. If you have too many plants to dig up, you can clip the flowerheads and dispose of them now to prevent seed production. It is advisable to wear gloves and protective clothing and wash your hands after controlling tansy ragwort. Mowing is not a recommended control method as cut plants will grow new stems and behave as a perennial.

Large infestations are better handled by a combination of control methods.

If blooming, cut and bag flowerheads, and put them in the trash.

Although it is too late to spray with herbicides right now, young rosettes can be treated in the fall and in the spring so they will not be a problem next summer. Herbicides containing the chemical glyphosate are readily available and can be very effective.

Other herbicides may also be used, so check with your local county weed board or extension office for further recommendations. Be sure to follow the label carefully.

Animals may need to be removed from areas that have been sprayed.

After tansy ragwort control, plant areas with site appropriate plants or seeds to provide competition and reduce further tansy ragwort invasions. Monitor areas for tansy ragwort seedlings and resprouts.

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