Noxious Weeds & Prohibited Plants: A Listing Guide

If you’ve ever looked at a yard, pasture, or forested site overflowing with weeds, then you understand how important prioritizing and planning are to successful weed control. At the state scale, there are two regulatory lists of introduced plant species that help set legal guidelines which can help counties, city, and land managers evaluate priorities.

  1. The State Weed Control Board defines the annual list of noxious weeds that indicates which species land managers should focus on and any species required for control in the State of Washington.
  2. The Washington State Department of Agriculture (WSDA) maintains a prohibited plant list that indicates which species are prohibited from transport, sale, or distribution in the State of Washington.

While the lists have common goals, they are two separate processes and thus do not overlap perfectly. This is why some listed noxious weeds can still be legally sold in plant nurseries (thankfully most nurseries are aware, so this is uncommon). Perhaps you’ve wondered how these lists get made or how you can add a qualifying species to one of these lists. This blog post will describe what the lists do and how Washington residents can play a role in their creation.

The State Noxious Weed List

Did you know that “noxious weed” is a legal term? All weeds on the state list have gone through the official legal process that is written into Washington state law.

A weed is not considered a noxious weed until it is officially listed on the State Noxious Weed List. To be considered, it must meet a certain set of qualifications; but qualifying ≠ automatically listed. To be listed, a species must be nominated and voted on through the official listing process.

So, what is a noxious weed? Taken from state law: “‘Noxious weed’ means a plant that when established is highly destructive, competitive, or difficult to control by cultural or chemical practices.”

Meaning, to be considered to be listed as a noxious weed, the plant species must meet the following qualifications:

  1. Introduced to Washington state (non-native)
  2. Spreads beyond where planted
  3. Creates harm in areas where introduced (i.e. has a negative impact on its local ecology, economy, and/or health)
  4. Difficult to control using a variety of methods

The State Noxious Weed Board identifies these species in their State Noxious Weed List. The list is updated annually and classifies weeds based on how widespread they are in the state. The three weed classes (A, B, & C) help us inform decisions on how to best use our resources. Class A weeds (least common) are not yet widespread, so we still have a chance to prevent them from spreading through early detection and rapid response. This is why they are required for control statewide. Whereas Class B weeds vary in abundance in different regions, so their regulation is based on their location. Lastly, Class C weeds (most common) are already abundant, thus eradication is an unreasonable goal, but education and targeted control efforts in sensitive areas are still crucial.  

A gradient of the three state noxious weed classes., A, B, & C. On the left is the least common and to the right it moves to most common. The graphic is also split in half with "required for control" on the left and "encouraged to control." on the right. Class A is on the far left on the required for control side. Class B is in the middle. Half is "designated" for control and half is not. while class c is on the far right and encouraged for control.

Eradication: Legally defined as eliminating a noxious weed within an area of infestation

Control: Legally defined as preventing the dispersal of all propagating parts capable of forming a new plant within a calendar year. This means not letting weeds reproduce, one example of this would be to remove a plant before it has a chance to produce seeds.

A: Distribution in Washington state is still limited. Eradication is required statewide. B: distribution is limited to portions of Washington state. control is required on a regional basis (where designated). C: Wide in Washington or are of special interest to the Agricultual industry. control not legally required by state. B & C: Counties can choose to require control where not designated by state.

Distribution maps illustrate the class rating system

  • Map of the state of Washington showing the relative distribution of the plant species garlic mustard: 4 of 46 counties show sizable infests.
  • Map of the state of Washington showing the relative distribution of the plant species purple loosestrife: 16 of 46 counties show sizable infests.
  • Map of the state of Washington showing the relative distribution of the plant species creeping thistle: 45 of 46 counties show sizable infests.

The Noxious Weed Control Board also maintains a monitor list of weeds that may need to be listed as noxious weeds in future years. More data and general information are needed for species on these lists to determine if they should be designated as a noxious weed or not. Species on this list are reviewed on a rotation to determine listing or delisting.

The Annual Process

The weed list may change annually, the process is described in detail on the state website and summarized below.

State Noxious Weed Listing Process. Step 1: Spring: Public Proposals: Proposals for changes to state noxious weed list accepted January 1 - April 30. Step 2: Summer: Review & Research: State Weed Committee reviews proposals, does in depth research and data review and determines if a species qualifies and then makes a recommendation for the board to consider. Step 3: Fall: State Level List. The state weed board hosts meeting online and open to public comment to discuss committee recommendation. The annual state weed list is made official here. Step 4: Winter: County level lists County weed boards host a meeting within 90 days of state vote that is open to public comment. They will discuss state required changes and additional county level proposals.  Annual county weed lists are made official following board vote.

Before being listed as a noxious weed (as detailed in the infographic above), the proposal will be reviewed by the following groups:

Requesting party

While anyone is welcome to propose changes and additions to the State Noxious Weed List, the most successful listing proposals are submitted by entities/groups versus individuals. This is because each proposal must withstand multiple levels of review and should be as thorough as possible. If you are an individual interested in listing a noxious weed, it is advisable to connect with a group who is actively controlling or surveying the species. County Weed Boards who wish to change the designation status of any particular species within their County will also propose those changes at this step.

State Noxious Weed Committee

The Committee is one of many under the State Noxious Weed Board. It is composed of scientists and experts in invasive plant management and control. The Washington State Nursery and Landscape Association and the Washington Native Plant Society are also represented on the Committee.

In May, the Committee will have their initial meeting to review submissions. During the summer, they will conduct any needed research on suggested changes to the weed list. This research may include literature searches, surveys of county programs, discussions with other states, and/or field investigations. In September, the Committee will vote on their final recommended changes and put together a technical report (written findings) that will be brought to the board in the next step.

State Noxious Weed Control Board

The Board is composed of nine voting members and three non-voting members, all volunteers.

  • Five are elected by members of County & District Weed Boards from various regions in the state
  • Six are appointed by the Director of the state Department of Agriculture
    • Three of the six are non-voting scientific advisers
  • One is appointed by the Washington State Association of Counties

In September, the Board will convene to consider the Committee’s proposals. Here they will decide which proposals will move on to the final vote. Agreed upon proposals will be made public. Public comments are accepted leading up to the final vote that is held in November. Here, the Board will consider all public testimonies in addition to the committee’s findings and make their final decision on changes to the weed list. The updated state weed list becomes active in January, and the cycle begins again!

King County Noxious Weed CONTROL Board

The County Board is composed of five voting volunteer members and one non-voting member from the County Extension office. Board members represent the five County weed districts. All County boards will hold a hearing within 90 days of the state vote. The County Board will vote on changes and the county level list will become active shortly thereafter. Counties are required to adopt all Class A’s and Class B’s designated in their region. In addition, County Boards may vote to require the control of species that the state did not.

In King County, our weed board has also developed a “Weeds of Concern” category. Much like the state’s “Monitor List”, it lists non-native species that are not designated by the state as noxious weeds but have impacts in King County and are considered invasive vegetation. This category allows land managers more flexibility with permits for removal of these “weeds of concern” in critical areas.

Prohibited Plants

The Washington State Department of Agriculture is also involved in reducing the impacts of noxious weeds. The Plant Protection Division maintains a list of species that are prohibited from transport, sale, or distribution in the State of Washington. Half of the state’s listed weeds are on the Prohibited Plants List (81/159). That includes all Class A weeds and many Class B and C weeds. This list also includes species that do not exist in Washington State, but we wish to prevent from getting here in the first place.

Adding a Species to the Prohibited Plant list

Proposal Development. Much like the noxious weed listing, proposals for the prohibited plant list must include thorough justification for listing the species. These proposals can be accepted at any time by the WA State Department of Agriculture’s Plant Services Program. Their email is  Petitions should be thoughtfully developed, include scientific and economic analysis, and ideally are done in collaboration with public agencies, municipalities or environmental organizations. The program encourages individuals who seek to engage in this process to connect with a state, regional or local agency to collaborate in developing a petition.

Internal Review. If the Agency Director approves a proposal for review, the following internal review stage can take up to two years of research and information gathering. Depending on the species, they may consult with the WSDA’s Nursery Advisory Committee made up of representatives from the nursery industry to evaluate potential impacts and feasibility.

Together these two state level processes help guide legal responsibilities for all landowners in the state. Both depend on others contributing to the listing process to keep the lists current and relevant. It’s a community effort that supports land managers statewide, both big and small.