King County encourages landowners to get a jump on noxious weeds

Springtime isn't just for growing flowerbeds and vegetable gardens – it's also the time of year when noxious weeds begin proliferating. The King County Noxious Weed Control Program has started its annual search for new infestations of noxious weeds and checking areas where weeds have been found in past years.

Last year, noxious weed program staff noted a big increase in occurrences of poisonous tansy ragwort in eastern and southeastern King County. This year, noxious weed program manager Steven Burke is urging city maintenance crews and private landowners to find and control infestations of tansy ragwort and other noxious weeds before they go to seed.

"Because this plant is toxic to animals and spreads rapidly in open areas, tansy ragwort is a serious threat to the county's agricultural lands," Burke said. "Tansy ragwort seeds last for at least 16 years in the soil, so every time we miss a few plants, we can expect another decade or two of headaches."

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.

Noxious weeds in waterways and natural areas are another primary concern of the noxious weed program. Information on all these noxious weeds is available on the county weed program's website: 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.

Burke said public agencies and landowners with designated noxious weeds on their property will be contacted and reminded that weed control is a landowner responsibility. Early identification helps landowners control and contain infestations before they become a time-consuming and expensive problem.

The costs of allowing noxious weeds to invade are enormous. Noxious and invasive plant species cost the U.S. economy an estimated $137 billion annually in damage and control costs. In King County, about $100,000 per year has been spent since 1995 to eradicate a single infestation of hydrilla, a Class A aquatic noxious weed.

The focus of the county's surveys includes a number of serious noxious weeds, including:

• Giant Hogweed – Often reaching 15 feet tall with huge leaves, thick, purple-blotched stems and broad umbrella-shaped white flower heads, this plant is a health hazard, causing painful blisters and scarring. Usually found in urban areas.
• Garlic Mustard – This fast spreading, shade tolerant plant is about two feet tall with small, white, four-petalled flowers and a garlic smell from the leaves and root. A recent invader in Washington, it is one of the worst weeds in other parts of the U.S. and is rapidly spreading in Seattle area parks and green spaces.
• Milk Thistle – A very large, aggressive thistle that can cause nitrate poisoning in cattle and is highly challenging to manage once it gets established in a pasture. The large, spiny leaves have distinctive white marbling and the large, pink-purple thistle flowers have thick spines around the base. So far the infestations have been mostly limited to the Enumclaw area.
• Sulfur Cinquefoil – This non-palatable plant can drastically reduce the value of a pasture and the control of an established population can take years. This plant resembles tall buttercup but has distinct 5-parted, hairy, toothed leaf clusters that are arranged like a hand and pale lemon-yellow flowers.
• Spotted and Meadow Knapweed – These open field invaders can spread quickly and out-compete plants that animals need for food. The purple and pink flower heads look like thistles but the leaves are small and without spines.
• Tansy Ragwort – This time of year the dark green ruffled-looking rosettes are present, developing stalks with yellow daisy-like flowers later in the season. This weed is toxic to livestock and frequently grazed in the rosette stage.
• Garden and Purple Loosestrife – These beautiful but damaging wetland plants can devastate fish and wildlife habitat and reduce the functions of waterways and wetlands. Look for the bright yellow and vivid purple flowers of these two plants from late June through August along lakeshores, streams and wetlands.

For a complete list of the noxious weeds on the county's list or to find out more about the noxious weed program, 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.