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.

“This year is shaping up to be one of the worst for tansy ragwort that we have
seen,” said Samuel Leininger, WeedWise program manager for the Clackamas
Soil and Water Conservation District (CSWCD). “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 tansy 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.

“The alkaloids in tansy will build up in the liver and cause irreversible damage
in grazing animals,” Dr. Cath Mertens, a local veterinarian, noted.
“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., “Please pay close attention to the hay you put
up or purchase,” Dr. Mertens said.

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 percent.”

“With little left for the insects to eat, the insect populations crash,” Price
added. “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.”

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 (https://bit.ly/3RSj8yZ) to help
residents with their control efforts.

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

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.