This year's prolonged wet weather is having the side effect of re-invigorating a noxious weed. The Northwest is seeing a comeback of tansy ragwort, a toxic species of sunflower that farmers thought they had vanquished years ago.

Tansy ragwort was practically eradicated using biological controls –- European beetles, moths and flies introduced to feed on the plant. This summer's cool weather, combined with a drop-off in the insect population, cleared the way for tansy to take off again, especially west of the Cascades.

Rick Johnson is the noxious weed control coordinator for Thurston County, Washington. He says the current generation of farmers and ranchers may not realize the yellow flowering plant in their pastures can be lethal to cattle and horses.

"Over the last couple decades with knocking back the population of tansy, we haven't seen livestock losses -– until this year," Johnson says. "And it's a very unattractive thing to watch when livestock die from tansy. It's very painful for them and it's kind of long."

Landowners can control tansy with herbicide. State and county agriculture offices say it's best to wait until fall to spray, and they recommend against mowing the plant down.

On the Web:

Tansy ragwort overview:

Pacific Northwest Weed Management Handbook:

Guide to Washington's invasive plants and animals:

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