Noxious Weeds FAQ

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What makes a plant a weed?

The classic gardener’s definition of a weed is 'a plant out of place' – that is, any plant that’s growing where it’s not wanted.

What makes a plant a noxious weed?

'Noxious weed' is the traditional, legal term for invasive, non-native plants that are so aggressive they harm our local ecosystems or disrupt agricultural production. These plants crowd out the native species that fish and wildlife depend on. They also cost farmers, orchardists and ranchers millions of dollars in control efforts and lost production – and that can make the food we buy more expensive.

So while ordinary weeds may be annoying, noxious weeds are a genuine threat to the natural resources, ecology and economy of our state.

Are all noxious weeds grasses or flowering plants?

No. The term noxious weed includes non-native grasses, flowering plants, shrubs and even certain trees. It also includes aquatic plants that invade wetlands, lakes, streams and shorelines.

Are all non-native plants invasive noxious weeds?

No. Only a very small fraction of non-native plants become invasive.

How do plants become listed as noxious weeds?

The Washington State Noxious Weed Control Board creates and maintains the state’s official list of noxious weeds. Citizens can nominate a weed to be included or dropped from the list, or ask that a weed’s classification be changed. For more information on the listing process and the weed list, click here.

What are the three classifications of noxious weeds?

Class A

Class A noxious weeds are usually newcomers. They are often found in only a few places in the state, and state and local weed boards hope to completely eradicate them before they get a foothold in Washington. Class A weeds are the ones you are least likely to see – but the ones that are most important to report. (If you see a plant you think might be a Class A noxious weed, please report it to your County Weed Board).

Class B

Class B noxious weeds are abundant in some areas of the state, but absent or rare in others. The goal for Class B weeds is to control and reduce their occurrence where they are abundant, and to prevent them from spreading to those parts of the state where they are rare or absent.

Class C

Class C Noxious weeds are already widespread in Washington. In some cases, counties may require property owners to control Class C weeds, but more often counties simply try to educate residents about why controlling them is a good idea.

What is the quarantine list?

The Washington State Department of Agriculture maintains a quarantine list of plants whose sale or distribution is prohibited. All Class A noxious weeds are on this list. There are also plants on the list to prevent them from being imported and spread in our state.

Why are there laws about noxious weeds?

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 laws define which invasive plants are classified as noxious weeds, and what plants are on the “quarantine list” of plants that are illegal to sell or distribute in Washington. The law also authorizes County Weed Boards and local Weed Districts to enforce requirements for landowner control of weeds.

Why are there both state and local Weed Boards?

The Washington State Noxious Weed Control Board has three main responsibilities: It establishes and maintains the state’s official list of noxious weeds, coordinates the work of County Weed Boards and local Weed Districts, and provides public education and publications for use by County and local Weed Boards. 

County Weed Boards and local Weed Districts survey their jurisdictions for noxious weeds, work with landowners to ensure that they are controlled, and educate local citizens about invasive plants and their impacts. They enforce state laws requiring the control or eradication of certain weeds. 

Are there penalties for failing to control noxious weeds on my property?

Yes. County Weed Boards and local Weed Districts enforce the laws. If a landowner fails to control noxious weeds, the Weed Board may come and control them and bill the landowner for doing so. They may also impose civil fines for failure to control weeds.

How do noxious weeds get here, and how do they spread?

Wherever people travel, we take plants and seeds with us – sometimes intentionally, sometimes accidentally. When settlers first came to Washington, they accidentally brought seeds of Canada thistle with them – a plant that is still a problem for farmers today.

Early settlers also brought scotch broom as an ornamental garden plant. It has spread all over Western Washington. In fact, about half of the invasive, noxious weeds in Washington are “escapees” from gardens.

Cars, cargo ships, hiking boots and even bicycle tires can all spread weed seeds, so the more people travel and trade, the more likely we are to accidentally spread weed seeds.

Wildlife and domesticated animals also spread weed seeds either through their digestive systems or when seeds are carried in their fur.

Are all noxious weeds poisonous?

No. Only a few noxious weeds are poisonous to animals or humans. Some native plants are also poisonous.

For information on poisonous plants in Western Washington: Visit the great pages on poisionous plants from King County and from Whatcom County.

For eastern Washington poisonous plants: Check out this excellent resource from Lincoln County.

How do noxious weeds affect fish and wildlife?

Noxious, invasive weeds crowd out native plants that fish and wildlife depend on for food. Invasive plants can disrupt or clog streams and lakes, and alter whole ecosystems. 

Here are two typical examples of the damage caused by invasive noxious weeds: When spotted knapweed invades mountain meadows, it crowds out plants that elk depend on, and can reduce the food supply for elk by 90%. 

When Brazilian elodea, a common aquarium plant, was dumped in a lake, it grew so fast and so abundantly that it infested miles of the Chehalis River. In some places, it slowed the flow of water, reduced dissolved oxygen, and caused silt to pile up, making the river more shallow and the water warmer. All these impacts degraded the habitat for salmon and other fish.

How do noxious weeds affect farmers, ranchers and orchardists – and the consumers who eat the food they grow?

Invasive, noxious weeds drive up costs for agricultural producers who have to control them with expensive applications of herbicides or by using labor-intensive mechanical methods. Noxious weeds can reduce crop yields and ruin crops grown for seed. When costs go up for food producers, the price of groceries also rises.

Why do noxious weeds grow so fast and become so aggressive?

In their native habitat, all plants have natural enemies– insects that feed on them, plant diseases that limit their growth, and animals that munch on them. They also compete with other native plants that help keep them in check.

But when these plants arrive in a new locale, their natural enemies and competitors don’t usually come with them. In a new location, there may not be any insects, animals, or plant competitors that inhibit their spread.

Plants that become invasive are also usually very adaptable to a wide range of soils and growing conditions, and able to reproduce and spread rapidly, especially in soils that have been disturbed by cultivation, fire, or other human activity.

Climate change is also a growing factor in creating conditions for invasive plants to spread rapidly in new areas.

Once a non-native plant is introduced here, shouldn’t we just let nature take its course?

Invasive species are the second leading cause of native species becoming endangered. So if we want to preserve native wildlife such as elk and salmon, we have to work hard to protect their habitats from invasive, noxious weeds. Farmers, ranchers, and orchardists also have a big stake in keeping invasive plants from getting out of control. In other states and countries, large land areas have become unusable for food production because they are so heavily infested with noxious weeds.

What can people do to prevent and control invasive 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. The Noxious Weed Control Board can send you a publication that offers non-invasive alternatives to some common garden plants that have become invasive: Eastern Washington Garden Wise or Western Washington Garden Wise.

Be careful when you travel. Seeds ride along in wheels, stick to your shoes, boots, clothing and pets. Clean these items before and after you travel or go hiking.

If you have a boat, be sure to clean it thoroughly between trips, so that you don’t spread plant fragments (or invasive mussels) from one lake or stream to another. This is the most effective way to prevent the spread of invasive aquatic plants and animals.

If you have invasive plants on your property, control or eradicate them so they don’t spread to your neighbors, to roadsides, or to natural areas. If you need help or advice, or need to know which plants to control, contact your local County Weed Board

Volunteer to participate in weed pulls and native plant restoration projects. Many non-profit organizations sponsor these events, and your County Weed Board can help you connect with them.

What is integrated pest management?

Integrated pest management is a way of using a variety of tools and techniques to control infestations that reduces reliance on herbicides. It includes: Prevention, including learning to recognize and eliminate invasive plants before they gain a foothold.

Cultural methods such as rotating crops and timing fertilizer applications to reduce weed growth. Biological controls use natural enemies, such as beneficial insects, that attack weeds and reduce their growth and reproduction. Herbicide methods use EPA-approved products, taking care to follow label instructions.