Protect horses by getting rid of tansy ragwort

Tansy ragwort is an invasive, toxic biennial weed from Europe often found in pastures and along roadsides.  It makes horses sick and can kill them if they eat enough of it.

Tansy ragwort can poison horses when they are exposed to it in pastures, hay and forage. Photo by Lisa Nelson.
Tansy ragwort can displace healthy forage plants due its aggressive growth. Photo by Ben Peterson.

The plant is also toxic to cattle, sheep, some goat breeds and people. Even though animals tend to avoid it, they can eat enough of it inadvertently to get sick or even die.  The biggest risk is when the plants have been cut down or are mixed in the hay because the plants are not as bitter then but still remain toxic.

Cattle can die from eating tansy ragwort. Photo by Maria Winkler.

Identifying tansy ragwort is not difficult and there are many photos below and on our website that can help you.

Tansy ragwort leaves are dark green on top, pale green below, have distinctive lobes and have a wrinkly or ruffled appearance. The outermost lobe is edged with blunt teeth, like on a castle wall. Photo by Sasha Shaw.
Tansy ragwort flowers are like small daisies with yellow centers and 13 yellow ray petals. Photo by Sasha Shaw.
When tansy ragwort plants are young, they grow in a basal rosette. Photo by Maria Winkler.
As a tansy ragwort plant matures, it bolts and forms flowering stems. This is the perfect time to pull the plants because they don’t have flowers yet and can’t form seeds and the root is weakened. Photo by Dennis Chambreau.
Tansy ragwort flowers from May to late summer and usually starts forming seeds in late July and August, sooner in very hot areas. A single plant can produce between 75,000 and 200,000 seeds and the seeds can remain viable in the soil for more than 10 years.

Tansy ragwort, called hierba de Santiago in Spanish and Senecio jacobaea in Latin, is commonly confused with a more widespread weed called common tansy,  tanaceto or hierba lombriguera in Spanish and Tanacetum vulgare in Latin.  Common tansy is also a European species and somewhat toxic, but it is not usually consumed by livestock due to its strong odor and bitter flavor.  The two “tansies” are most easily distinguished by their flowers. Tansy ragwort flowers have 13 external ray petals and common tansy has button-like flowers with no external ray petals.

Control Methods
Dig out plants with a shovel or pull out the plant, complete with roots. If there are flowers, cut off the top and bag it up for disposal in the garbage.

King County noxious weed specialist controlling tansy ragwort by cutting off the flowering top.  Photo by Sasha Shaw.

If you have a large infestation, we can give you advice on the best method for the site. The most important thing is to stop the plants from going to seed so you can prevent the plants from spreading more. Read more about controlling tansy ragwort here: in English or en español.

Large infestations of tansy ragwort can by controlled by pulling but it can take a lot of time and effort. Make sure to bag all the flowering plants to prevent seeding. Photo by Maria Winkler.

Keep animals out of infested pastures.  They will try to avoid eating tansy ragwort, but it is better to be safe than sorry. Try to keep your pasture free of toxic plants like tansy ragwort by keeping it healthy and watching for the plant throughout the year.

Horses will try not to eat tansy ragwort but even small amounts can build up in the liver and cause damage. Photo by Maria Winkler.

Please tell us about any tansy ragwort you see in King County. You can call or email our program or simply report it online on our website. Tansy ragwort is a regulated noxious weed in King County and everyone is required to control it, including the government. Please help us find it so we can make sure it gets controlled.

Tansy ragwort that is mowed when it is in seed will be much worse the following year, such as in this field. Photo by Sasha Shaw.

If you have any questions, please contact us. Thank you for helping us stop the spread of this dangerous noxious weed!

The horses will thank you for controlling tansy ragwort and other toxic weeds!


  1. Thank you for the article. I will give it to folks in my community that are unaware of how to manage these noxious weeds.

  2. Horses will not eat living ragwort unless they are starved, the only real danger is if it gets into hay. Provided they have other grazing as well, sheep will not be harmed by eating ragwort.

    • Thanks for the helpful information. I agree that horses won’t eat living tansy ragwort when they have plenty of healthy food. I am always sad when I see situations where they do eat it, because that likely means there is little else for them to eat. Also, I used to teach that tansy ragwort couldn’t hurt sheep, but I was informed by a sheep farmer that it does hurt them if they eat enough, which they do sometimes, so I’ve stopped saying it is harmless to sheep. As you point out, it is all about giving your animals healthy food so they won’t be forced to eat plants like tansy ragwort. I believe a healthy pasture and quality hay is the best strategy!

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