Noxious Weed Control

What are noxious weeds?

According to the Washington State Noxious Weed Control Board, “‘Noxious weed’ is the traditional, legal term for any invasive, non-native plant that threatens agricultural crops, local ecosystems or fish and wildlife habitat.”

The Washington State Noxious Weed Control Board designates which weeds are included on the state weed list; control of weeds on the list can then be made mandatory. Counties then have the ability to designate noxious weeds as required control in their own jurisdictions.

The law under which state and county weed boards operate is RCW 17.10; monetary penalties for failing to control required noxious weeds can be found here. For a list of noxious weeds in your area, please consult the Washington state, Clallam, and Jefferson county weed lists.

Spotted and Meadow Knapweeds

Spotted knapweed and meadow knapweed are perennials with many stems and pink to purple flowers. Mowing will temporarily delay flowering, but will not control the plants as they will keep trying to produce flowers until successful.

Canada Thistle

A noxious weed named Canada Thistle.Canada thistle is an aggressive, creeping perennial that spreads by both seeds and especially by underground rhizomes. As Canada thistle can sprout from underground root fragments, it is important to kill the roots in order to control this plant.


Scotch Broom

Scotch broom is a common sight along the roads on the Olympic Peninsula. This yellow flowered perennial shrub produces pods that pop upon maturity, releasing seeds into the surrounding environment.

Poison Hemlock

As its name suggests, all parts of poison hemlock are acutely toxic to animals and humans. Care should be taken when handling poison hemlock plants; gloves should be worn and hands washed prior to eating or smoking. Poison hemlock is similar in appearance to many other members of the carrot family; plants have finely divided leaves and produce clusters of small white flowers. Under normal conditions, poison hemlock is a biennial, growing as a rosette the first year and producing flowering stems the second. Poison hemlock cannot be controlled through mowing as plants will continue to regrow until they can successfully flower. Instead, poison hemlock plants must be controlled chemically or may be dug as long as the entire tap root is removed. As each plant can produce a thousand seeds that can last many years in the soil, the most important part of controlling a poison hemlock infestation is preventing all plants from setting seed. Control of poison hemlock is mandatory in Clallam and Jefferson counties.

Tansy Ragwort

Tansy ragwort is a biennial in the Sunflower family. Tansy ragwort is toxic to livestock, both fresh and if dried in hay. Tansy ragwort grows as a low growing rosette in the first year with deeply incised leaves. In the second year, tansy sends up flower stalks with many dime-sized yellow flowers. Mowing will not control tansy ragwort; plants need to be dug up at the root or may be treated chemically.