September 11, 2000
County board gaining ground on noxious weeds
by Lisa Allen
Valley View Editor
Tansy ragwort plants grow abundantly in western Washington, but nowhere are their bright yellow flowers more visible than on rural roadsides. Their petals have faded now, but the plants that survive will be back next year, and so will their kids. Lots of them. One plant can produce 150,000 seeds that can spread for miles on the wind.
After taking root, the poisonous plant will grow for a year before it develops flowers. But it can still kill by destroying the livers of farm animals that graze on infested pastures or eat hay contaminated with the dried plant.
Tansy is considered a noxious weed. Other problem weeds in King County include giant hogweed‹a tall plant that can cause skin irritation, purple loosestrife that chokes lakes, and the pesky knapweed.
Increasing infestations of those weeds resulted in the creation of the King County Noxious Weed Control Board four years ago.
But the weeds had a big head start and there has been a lot of catching up to do.
In fact, tansy ragwort was so widespread a few years ago, the board almost gave up trying to control it.
"It has been a daunting task," says Jane Wentworth, weed program coordinator.
A couple of years ago, the County Council, to help fund the effort, enacted an assessment of 85 cents per parcel of land, plus nine cents an acre.
And, even though tansy is still a common sight along the roadsides, the eradication program is beginning to work, Wentworth said.
The assessment, which generates about $500,000 a year, has paid for eight part-time seasonal employees who work seven to eight months out of the year. That's up from six workers who were on the job four months out of the year.
"Those extra months make a big difference," said Wentworth. "We have identified more weed-infested sites than ever before."
Where the invaders decide to set up camp depends on the weed, she said.
"The giant hogweed is an urban weed," she said. "There are almost 1,000 infestations throughout the county."
The board does not do actual weed control, she said. Rather, the assessment pays for educational programs and technical assistance to landowners.
"The state weed law does require people to control weeds," she said. "The good news is that more and more people are calling us to try to get help to clean up weeds and also to try to get the county to do it, as well."
Wentworth said that according to state law, property owners can be fined for not controlling weeds, but that the board prefers to try to get landowners and the county to work together. However, the county has been short of funding for weed removal.
"Weeds along roadways are very visible," she said. "The county should set an example for landowners. If one person cleans up weeds, it doesn't do much good if the neighboring parcel is still infested. Everyone has to work together. It is as much a public land as a private land problem."
But Wentworth added that control is getting better every year.
"Every year we do more surveys," she said. "But there will always be room for improvement."
As far as control measures go, the board recommends that small infestations be dealt with by hand pulling, she said. Spot spraying on a limited basis with a selective herbicide will also work.
"We want to look at a more integrated management strategy to get weeds to a manageable level, so we don't rely so much on pesticides," she said. "And although mowing helps control some weeds, it is not effective for tansy. It just spreads the seeds."
Wentworth says the tansy plants should be dug up or the flower heads should be cut and gathered and placed in plastic bags in order to prevent seed spread.
"Fall is our last chance to keep seed production under control," she said. "It is a two-step process to break the cycle. We need to stop seed production and spread, and also get rid of the first-year plants (in a rosette stage) so they don't flower the next year."
She noted that there is a similar yellow flowering plant‹the common tansy‹that is not considered a high priority noxious weed. The difference is in the petals‹tansy ragwort has 13 small yellow petals on each flower. Common tansy has no petals.
"We really rely on compliance of public and private landowners," Wentworth said. "They need information on how to deal with noxious weeds. And we are there to offer assistance."
For further information on noxious weeds, call the King County Noxious Weed Control Board at 206-296-0290.
Lisa Allen/staff photo
Tansy ragwort, a weed poisonous to livestock, is common along roadways.