Yellow Tansy Flowers Have Neighbors Seeing Red

Unmanaged tansy ragwort threatens an adjacent hay field. Photo: Samuel Leininger, Clackamas SWCD

Unmanaged tansy ragwort threatens an adjacent hay field. Photo: Samuel Leininger, Clackamas SWCD

Bouquets of yellow flowers are blooming across our region. Unfortunately, these colorful blooms are from the poisonous plant known as tansy ragwort. They have many residents feverishly working to protect their fields and livestock.

A Banner Year for Tansy is a Dangerous Year for Livestock

“This year is shaping up to be one of the worst for tansy ragwort that we have seen,” says Samuel Leininger, WeedWise program manager for the Clackamas Soil and Water Conservation District. “Weather conditions this year resulted in perfect conditions to allow these plants to flourish. We are receiving calls from concerned residents across Clackamas County.”

By the time their flowers appear, the best management of this weed is a good pair of leather gloves and a healthy dose of perspiration from pulling mature plants. Mowing and cutting do not kill the plants and only spreads the poisonous vegetation.

Tansy ragwort (Jacobaea vulgaris) has long tormented hay producers and rural landowners who graze livestock. Horses and cows are especially susceptible to this poisonous weed.

Dr. Cath Mertens, a local veterinarian warns, “The alkaloids in tansy will build up in the liver and cause irreversible damage in grazing animals. They will generally avoid eating this weed unless there is nothing else available. The best thing to do is to make sure your horses and livestock always have something available to eat other than tansy.”

Contaminated hay is also a problem because it becomes impossible for feeding animals to avoid tansy. Dr. Mertens urges livestock owners, “Please pay close attention to the hay you put up or purchase.”

What About the Insects that Attack Tansy Tagwort?

In the 1960s and 70s, two insects known as the cinnabar moth and the tansy ragwort flea beetle were released in Oregon. These biological control insects have been effective, but they follow a boom-bust cycle. According to Joel Price, biological control entomologist for the Oregon Department of Agriculture, “Two years ago the tansy ragwort population was very high, but the following year the biological control insects had reduced the tansy ragwort population by 95%.”

Price goes on to explain, “With little left for the insects to eat, the insect populations crash. In a normal year, there would be time for the biocontrol population to build up. However, the historically wet spring is causing problems for the flea beetle. This insect overwinters in the ground and the overly wet spring is keeping it from reproducing quickly enough to help control this year’s tansy explosion.”

Dispose of tansy properly to keep from spreading seed.

Dispose of tansy properly to keep from spreading seed.

To Protect Local Livestock, We Need Everyone to Pitch In!

Tansy outbreaks not only poison livestock but also affects the relationships of neighbors. In Clackamas County, there are no longer weed inspectors to regulate tansy ragwort, so residents are encouraged to work with their neighbors to control this weed.

Tansy ragwort is manageable. Residents are encouraged to focus on areas that are grazed and along fence lines to help prevent plants from spreading. Flowering plants can be pulled and composted away from grazing animals or disposed of as trash. Residents are also encouraged to plan for the coming year to prevent plants from blooming. The Clackamas SWCD has developed Tansy Ragwort Best Management Practices ( to help residents with their control efforts.

“More than ever, we need neighbors working together to protect pets and livestock from potential poisoning”, says Samuel Leininger.

Contact Us for More Information

If you have questions about steps you can take, please contact the Clackamas Soil and Water Conservation District at 503-210-6000 for more information.

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Clackamas SWCD