Tansy ragwort is a perennial nuisance to rural landowners in King County, and the county’s Noxious Weed Control Program notes that fall and winter are good times to help get rid of the vexing vegetation that causes serious health problems for livestock.

Treating tansy ragwort in its rosette stage is much easier than doing the control work later on when the plants are bolted and flowering, weed control officials note. Plants can be dug up manually, removing the roots. This is much easier in the winter and spring, when soil is soft and wet. Full removal of all of the roots is essential to good control efforts. This is because tansy ragwort can reproduce from broken root fragments left behind in the soil.

Because of the longevity of ragwort seeds in the soil, followup work is required for more than a year. Removing the rosettes in the spring and fall of every year is a great way to work toward eradication with the least amount of effort, according to Matt Below, a noxious weed control specialist for the county.

Tansy ragwort appears as bright yellow flower clusters in fields and on some roadsides. The plant is originally from western Asia and Europe, but has become well-established here and in other areas of the United States. The problem with tansy ragwort is that it’s toxic to livestock, particularly cattle and horses. The foliage contains pyrrolizidine alkaloids that cause cumulative liver damage, which can lead to problems such as extreme weakness, digestive problems, restlessness, lack of coordination, paralysis and wasting.

Tansy ragwort also outcompetes pasture plants and desirable native species, Below said.

More information is available from the Noxious Weed Control Program at (206) 296-0290, noxious.weeds@kingcounty.gov and www.kingcounty.gov/weeds.