County noxious weed specialists on the look out for infestations of the worst plant invaders

2005 Archived News

In order to catch newly invading noxious weeds before they spread, the King County Noxious Weed Control Program has started its annual search for new infestations and checking on those found in past years. The program tracks noxious weeds throughout the county that are listed on the Washington State Noxious Weed List. Program staff tell county and city agencies where the noxious weeds are growing and how to control them so they can work to reduce the impact of noxious weeds on public resources. The program also works with landowners to determine the best control option for weeds on their properties that are designated for control in the county.

Controlling noxious weeds is everyone's responsibility. Now is the time to take action against the invasive plants that are damaging our lands and waterways.

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. A plant can be declared a noxious weed if it seriously threatens the environment, agricultural productivity, public health or recreational use of natural areas.

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 weed infestations before they become a time-consuming and expensive problem. 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.

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 (Hydrilla verticillata), a Class A aquatic noxious weed. The City of Seattle estimates that it costs $20,000 per acre to restore an urban forest infested with invasives.

The focus of the county's surveys includes the following serious noxious weeds:

• 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 greenspaces.
• 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.

County weed specialists will also be looking for other noxious weeds on the county weed list and plants new to the noxious weed list, such as common reed (a very tall wetland grass also called phragmites that has taken over a wetland by the 1st Avenue Bridge in Seattle).

To find out more about the noxious weed program and the county noxious weed list, please call 206-296-0290; e-mail noxious.weeds@kingcounty.gov; or visit the Web site at 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/wlr/lands/weeds/infestations-form.cfm.