The Dirt on Noxious Weeds

Weed Cartoon 2 Planning this year’s garden also means gearing up to battle weeds — and noxious weeds in particular will keep us constantly vigilant. Get a head start with these FAQs from the Washington State Noxious Weed Control Board.

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.

Variable Leaf Milfoil,  an aquatic invader.

Variable Leaf Milfoil,
an aquatic invader

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, click here.

Garlic Mustard

Garlic Mustard.
Self-fertile & shade tolerant.

What are the three classifications of noxious weeds?
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 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 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.

Yellow Devil Hawkweed.

Yellow Devil Hawkweed.

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.

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.

An infestation of Purple Loosestrife.

An infestation of
Purple Loosestrife.

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.

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, 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.
  • 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.
  • 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.

If you need help or advice, or need to know which plants to control, contact your local County Weed Board.
For more info and a complete list of Class A, B, C & Quarantined noxious weeds, visit the Washington State Noxious Weed Control Board.

All photos courtesy WA NWCB.


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