King County in a race against the clock to stop the spread of toxic tansy ragwort

When a pasture owner in Maple Valley had three of her horses die mysteriously several years ago, it wasn't until a necropsy on the third horse revealed the culprit: Poisoning from the noxious weed, tansy ragwort.

"This particular field in Maple Valley is mostly free of tansy ragwort now, thanks to the property owner's diligence," said Dennis Chambreau, King County weed specialist. "However, this property owner will need to watch for new plants for many years to come because the seeds can remain viable in the soil for up to 16 years."

Elsewhere in King County, tansy ragwort is in full flower and threatening to go to seed. The King County Noxious Weed Program urges property owners to act now by pulling and bagging any tansy ragwort plants they find on their property.

Chambreau said the invasive plant is poisonous to animals and can cause irreversible liver damage when it is eaten. Even small amounts of tansy ragwort can be a problem if the exposure continues over a long time. While most animals avoid eating tansy ragwort, the plant’s low-growing rosettes sometimes mix with grasses and can’t be avoided. Tansy ragwort that is accidentally cut and included in hay tastes sweeter but remains toxic.

County residents are also encouraged to contact the noxious weed program if they see any tansy ragwort that isn't being controlled on roadsides or elsewhere, especially in areas with livestock nearby.

"County weed specialists are driving the roads throughout the county and following up on past infestations to look for tansy ragwort and other noxious weeds," said Sasha Shaw, education specialist for the King County Noxious Weed Program. "We are working with property owners, public land managers and roadside vegetation crews to make sure the plants are removed before they go to seed."

This time of year, tansy ragwort is covered with many small, yellow daisy-type flowers with yellow petals and a yellow center and is usually between two and four feet tall, although it can be much shorter if mowed.

"Tansy ragwort can form seeds if pulled or mowed when it is in flower, so it is important to pull and bag flowering plants and discard with the garbage to avoid spreading the seeds," Shaw said.

Flowering plants should be put in the garbage section, not yard waste, and plants should be bagged or covered securely during transport because of the risk of seeds escaping. Property owners can contact the county noxious weed program for a voucher to cover the cost of disposing tansy ragwort at a county transfer station.

Noxious weed specialists will be available to answer questions about tansy ragwort and other noxious weeds at the King County Fair in Enumclaw, July 19-23.

The King County Noxious Weed Program tracks tansy ragwort and other state-listed noxious weeds and provides information on how to best manage infestations. If property owners think they may have a noxious weed such as tansy ragwort, the noxious weed program can help identify the weeds and give advice on control methods.

Noxious weeds are non-native plants that are aggressive, competitive and difficult to control. "Noxious" does not mean toxic, although a noxious weed can have toxic properties, such as milk thistle and tansy ragwort. A plant can be declared a noxious weed if it seriously threatens the environment, agricultural productivity, public health or recreational use of natural areas. Information on noxious weeds is available on the county weed program’s Web site: http://dnr.metrokc.gov/weeds/.

King County's noxious weed program focuses on education, helps landowners identify noxious weeds and offers technical assistance on the best control options for each site.

For a complete list of the noxious weeds on the county's list or to find out more about the noxious weed program, please call 206-296-0290; e-mail noxious.weeds@kingcounty.gov; or visit the Web site at http://dnr.metrokc.gov/weeds. To report a noxious weed infestation in King County, call the program or use the online form at http://dnr.metrokc.gov/Weeds/infestations-form.cfm.