The 10 worst weeds

  • Reported by Alejandro Dominguez
  • Thursday, June 2, 2011 12:01am
  • Local News

Noxious weeds are invasive plants that change the environment by pushing out species naturally found here. In 2010, Snohomish County had a budget of about $250,000 to kill or control the spread of noxious weeds. Here are the top 10 noxious weeds in Snohomish County. [Gallery]

There are about 100 species of noxious plants that should be eradicated, according to the Snohomish County Noxious Weed Control Board. Some arrived as plants sold for gardens or landscapes. Of those on the control board’s list, 34 are confirmed to be in Snohomish County.

Weed control: For more information on noxious weeds, you can contact the Snohomish County Noxious Weed Control Board at 360-435-7830 or 800-562-4367. The control board is at 26718B 115th Ave. NE, Arlington. Its website is here.

Other useful sites:
• Washington State Noxious Weed Control Board
• King County’s noxious weed site (more detailed than Snohomish County’s)
• WSU Master Gardener’s noxious weeds information

To learn more about the plants listed as noxious weeds in Washington state, click here to go to the USDA’s site.


Knotweed: This shrub-like perennial looks like bamboo and can grow up to 10 feet tall. It causes problems in river ecosystems, such as that along the Skykomish, because it affects water temperature, which threatens salmon redds, or nests of eggs. Herbicides only work on this resilient weed in the fall when it tries to produce seeds. The county received a grant to fight it. [Gallery]

Hawkweed: The most widespread are the yellow and orange hawkweed: They have small, bristly hairs that cover the stems, leaves and flower buds. They are mostly found along walking trails and side roads, especially in Granite Falls near the Mount Loop Highway. The county is waiting for a grant to help pay for controlling it. [Gallery]

Purple loosestrife: Known as “the wetland killer,” this small plant clogs irrigation canals and drainage ditches. It has purple to magenta flowers with five to six petals. A visible nest of it is underneath the U.S. 2 trestle in Everett. Every year, the county releases a non-native beetle that only eats this plant. Herbicides can only be used with a permit if the weed is near water. [Gallery]

Tansy ragwort: This 13-petal, daisy-like flowering plant is often found in empty fields, unkempt grounds and even where horses roam. It causes liver damage in livestock that eat it. It’s abundant in Clearview and Maltby. The county only focuses on this plant along roads. [Gallery]

Canada thistle: The small purple-pinkish flower is so widespread that the county can only act when someone reports it to the department. Containment has fallen mostly to homeowners. Herbicides can be effective. [Gallery]

Giant hogweed: The 15-foot plant has been used in landscaping in the past. When exposed to sunlight, its sap can cause second-degree burns on human skin. The plant has been contained to 15 private sites in the county. Call the noxious weed control board if you find one. Round-up is effective. [Gallery]

Poison hemlock: This aromatic plant is found mostly in Stanwood and the lower part of Snohomish. Its most distinguishing feature is a smooth stem with purple splotches. All of the plant is toxic for livestock and humans. Wear gloves to dig it out. Bag the seeds and flowers and throw them into the trash. [Gallery]

Diffuse knapweed: This flower with purple or white petals colonizes everything in its way. If it’s found in your garden, mowing it is not recommended. The weeds must be pulled early before they go to seed. [Gallery]

Butterfly bush: This shrub can have up to 15-foot branches and 10-inch bell-shaped pink flowers. A landscaping plant, it has spread in river corridors and urban areas. The best way to get rid of it is to cut the flowers off and pull it out. [Gallery]

English ivy: You can tell this ivy by its heart-shaped leaf. It’s found throughout the county and climbs over large trees, making them heavier and more prone to fall from strong winds. To eradicate, the vines must be pulled from the roots. [Gallery]

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