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Noxious weeds

King County, Washington

To offer a suggestion or report an error on the King County Noxious Weeds website, please contact Sasha Shaw, education specialist.

KC Weed News - May 2005

Topics Below

Weed of the Month: Giant Hogweed (Heracleum mantegazzianum)

If you ever see a full-grown giant hogweed plant, you will not forget it. And if you have the misfortune to stumble into a ravine filled with giant hogweed, you will think you have entered a scene straight out of the 1950’s horror movie Day of the Triffids. If you manage to escape unharmed, then you should immediately call the noxious weed program so we can help you fend off this giant invader.

People who wanted a dramatic centerpiece plant once introduced giant hogweed into some of the nicest gardens in western Washington. These people unfortunately weren’t aware of the experiences of gardeners in England, upstate New York, Ontario, Pennsylvania and Vancouver Island. Wherever this plant has been introduced, it has escaped into ravines and riversides and pushed out native plants, increased erosion and burned the skin of anyone unfortunate enough to get too close. The band Genesis has a song called “Return of the Giant Hogweed” that says it all:

Turn and run!
Nothing can stop them,
Around every river and canal their power is growing.
Stamp them out!
We must destroy them,
They infiltrate each city with their thick dark warning odour.

Fashionable country gentlemen had some cultivated wild gardens,
In which they innocently planted the Giant Hogweed throughout the land.
Botanical creature stirs, seeking revenge.
Royal beast did not forget.
Soon they escaped, spreading their seed,
Preparing for an onslaught, threatening the human race.

Unlike its smaller, less aggressive cousin cow parsnip, giant hogweed is not native to the United States. Hogweed evolved in the rugged ravines and swamps of the Caucasus Mountains and southwestern Asia and left behind any natural enemies that would have kept it in check. As a result, the populations in King County spread without natural controls and with an unfair advantage over native plants.

Since our program began in 1996, we have found over 1300 properties with giant hogweed. Most of these are small patches, often only a few plants, but some are large and scary and take many years to remove. This year we have already found hogweed on close to 200 properties, including one infestation covering over 10,000 square feet, and there are still many more to check. Based on last year, we expect to find about 400 properties with hogweed by the end of the season. We have found giant hogweed in most of the neighborhoods of Seattle as well as in Tukwila, Burien, Skyway, Renton, Issaquah and even in rural areas such as Vashon, Duvall, the Union Hill area and Carnation. Our staff helps anyone who needs help to control giant hogweed. It is in all of our interests to keep this plant from spreading any further and to eradicate it wherever possible.

If you have any concerns about giant hogweed or spot any new infestations, please contact us at or use our online form at Infestations Form.

Proposed Changes to the Washington State Weed List

Our weed board has sent in proposals to the State Noxious Weed Committee to add two new plants to the state noxious weed list for 2006: floating primrose willow (Ludwigia peploides) and yellow archangel (Lamium galeobdolon). The first plant is a close relative of water primrose (Ludwigia hexapetala), which has proven to be so invasive in sloughs along the lower Columbia River and elsewhere. The second plant will be familiar to many gardeners and homeowners as the silver and green Lamium used widely in flower baskets, garden beds and as a shade-tolerant groundcover. Unfortunately, yellow archangel is also becoming an all-too-common sight in forested parks and shady ravines in the county, where the plant spreads from backyard plantings and discarded yard waste. If you would like more information or if you have information on either of these plants, please contact Sasha Shaw,, 206-263-6468 or Steve McGonigal, Washington State Noxious Weed Board at or 360-902-2053.

Upcoming Trainings on Noxious Weeds

The noxious weed program is holding workshops on invasive plants and noxious weed management that are free and open to the public. The goals and topics for these vary and there may be space limits so please contact me for more information if you are interested.

  • May 11, 9:00am-12:00pm, City of Kent Bldg, 5821 W. James St, Kent – South King County noxious weed management workshop for vegetation management crews and agency staff. WSDA recertification – 3 credits (register with Sasha Shaw,, 206-263-6468)
  • May 11, 6 :30pm-9:00pm, Vashon Island – WSU Forest Steward Training on invasive plants, will also be open to other Vashon landowners, space permitting (for more info or to sign up, contact, Amy Grotta, WSU Extension, 206-205-3132)
  • May 17, 1:00pm-4:00pm, Bothell Regional Library, 18215 98 th Ave NE – North King County noxious weed management workshop for vegetation management crews and agency staff. WSDA recertification – 3 credits (register with Sasha Shaw,, 206-263-6468)
  • June 14, 6:30pm-8:30pm, Olympic View Elementary, 504 NE 95th St., Seattle – invasive plant management workshop for community members, volunteers, non-profits and other people interested in reducing the impact of invasive plants (register with Sasha Shaw,, 206-263-6468)
  • June 27, 6:30pm-8:00pm, Maple Valley Library, 21844 SE 248th St., Maple Valley – pasture and invasive weed workshop for pasture owners, homeowners and anyone else interested in learning more about invasive and noxious weeds causing problems in east King County (register with Sasha Shaw,, 206-263-6468).

We are also holding workshops and presentations for many specific groups such as the Leschi Community Council, Native Plant Stewards, Burien Habitat Stewards, Bellevue Streamside Owners and others. Please contact Sasha Shaw ( or 206-263-6468) if you would like a presentation on invasive plants or noxious weeds for your group, staff or community.

Weed Info Booths in May

  • May 7, Mercer Island Ivy Olympics, Island Park Elementary School, 9:30-4:00
  • May 14, Tukwila Backyard Wildlife Fair, Tukwila Community Center, 10-3:00
  • May 21, Celebrating Wildflowers, Woodland Park Zoo Family Farm, 9:30-3:00

If you would like more information or would like to schedule an invasive plant display table at your community event, please contact Sasha (206-263-6468).

Woodland Park Zoo’s Invasive Species Forum
Thursday, May 5 at 7:00pm

Free. Education Center Auditorium, N. 50th Street & Fremont Avenue N. Free parking in the zoo's south lot. Please join Dr. Tierney Thys and Dr. Sarah Reichard for a community forum at Woodland Park Zoo on the issue of non-native species of plants and animals that are invading our gardens, parks and streams, and out-competing native species. Accompanied by a brief segment on the invaders from the PBS series, National Geographic's Strange Days on Planet Earth, Tierney Thys and Sarah Reichard will lead a discussion with the audience on efforts nationally and locally, and what we can do.

Native Plant Appreciation Week, May 1-7

Make sure to pull some invasive weeds this week in honor of native plant appreciation week, May 1 to 7. And if you can’t find time this week, don’t worry if you are a bit late, the plants will appreciate your help anytime. Check out the WNPS website ( and the county website for more information and a ton of useful resources.

Washington State Bioagent News

There is a new email newsletter on biocontrol produced by WSU Extension’s Integrated Noxious Weed Invasive Species Project (INWISP) Coordinators. If you aren’t already receiving it and would like to or for more information, contact Tara Zimmerman at or 206-205-3203.

New Grant Opportunity from National Forest Foundation

The National Forest Foundation has a new Centennial Year Challenge award opportunity.  Proposals are due on May 20, 2005.  This opportunity is available to nonprofit partners working with the Forest Service across the country. Applications will be accepted from non-federal partners, community-based organizations, Native American tribes, and other nonprofit 501(c)(3) organizations. Applications cannot be accepted from federal, state or county agencies. Among the projects to be considered, the NFF will is looking for projects that address the damaging spread of invasive species on and around national forests and grasslands nationwide through project activities such as: removal and control of noxious weeds; citizen-based monitoring and GIS-mapping in areas of high infestation; watershed health improvement through re-seeding of riparian areas with native species; and cultivation of native species for restoration use. For more information contact Alexandra Kenny, Director, Grants Programs, NFF, 202-298-6740 ext 3, or Dan Hall, Project Associate/Office Manager, NFF, 202-298-6740 ext 3, or visit the NFF website at