Noxious Weed Information

What Are Noxious Weeds?

Noxious weeds are plant species that have been designated "noxious" by law. They are non-native plants that have been introduced to Washington through human action. Because of their aggressive growth and lack of natural enemies in the state, these species can be highly destructive, competitive or difficult to control. These plants crowd out the native species that fish and wildlife depend on. While ordinary weeds may be annoying, noxious weeds are a genuine threat to the natural resources, ecology and economy of our state. The Washington State Noxious Weed Control Board establishes which plants are noxious in Washington State.


Infestations of noxious weeds are devastating and have far-reaching impacts. They can create mono-cultures that destroy native plant communities and animal habitat, reduce crop yields, damage recreational opportunities, poison humans and livestock, lower land values, and clog waterways. Noxious weed infestations are the second leading cause of wildlife habitat loss.

To protect our land and resources many weed species have been placed on a special list in Washington State that mandates their control (WAC 16-750). The Washington State Noxious Weed Control Board develops the list each year. Learn more about the Weed Listing Process.

Where Did They Come From?

Most of our noxious weed species are native to Eurasia and or the Mediterranean region and were transported to the United States both accidentally and intentionally. They came in the ballast of ships, in the fleece and hair of livestock, in clothing, as contaminates in seed lots, and as ornamental plants.

In addition, these invaders were introduced without the natural enemies, such as insects or diseases that helped keep their populations in check in their native land.

How Are Weeds Spread?

Humans and their vehicles spread noxious weeds. They hitch rides on hiking boots, clothing, tires, boats, etc. Wildlife and domesticated animals also spread weed seeds either through their digestive systems or when seeds are carried in their fur. Weeds have been found as contaminates in flower seeds, and hay or straw. They can also be spread by wind and by water.

Who is Responsible for Weed Control?

RCW 17.10.140 holds landowners responsible for controlling noxious weeds on their property. Noxious weeds are everyone’s problem. When one landowner fails to control them, they spread to others’ property where they can cause great harm and reduce property values. Weed laws are needed to ensure that we all do our part to prevent this from happening. The weed board will provide assistance in identifying noxious weeds, and advice on control options. Voluntary compliance with Washington's weed law is encouraged. If a landowner refuses to control their noxious weeds the weed board, as authorized by state law, can arrange for the control work to be done and bill the landowner for costs incurred.

Control Methods

Because some plants are extremely difficult to control once established early detection and prompt control is very important. Successful long-term management of noxious weeds relies on a combination of methods: cultural, mechanical, biological (insects), herbicide use, and prevention activities. Often, you may obtain the best results by using several of the control methods together.

Whichever method or combination of methods is used, if it is employed for only one season, the weeds will most likely be back in a year or two. Contact our office for help with control options.

What Can People Do to Prevent Noxious Weed Infestations?

Be careful what you plant. Since half of all our noxious weeds are escapees from gardens, ask questions before you buy plants or seeds. We can send you a "Garden Wise" publication that offers non-invasive alternatives to some common garden plants that have become invasive, or you can download a copy of the Western Washington Guide (PDF) or the Eastern Washington Guide (PDF).


If you have a boat, be sure to clean it thoroughly between trips, so that you don’t’ spread plant fragments from one lake or stream to another.
