Using herbicides

We selectively and carefully use herbicides along our roadway and at the edge of water to minimize the risk to human health and the environment. This site includes our toxicology fact sheets for each herbicide used.

Purpose and need

We use herbicides, substances toxic to plants, as part of our vegetation control activities. Recognizing their potential risks to health and the environment, our crews use herbicides minimally and only when necessary.

We apply herbicides to:

  • Maintain a vegetation-free strip at the edge of the pavement, where necessary.
  • Selectively remove unsafe and undesirable plants.

Herbicides help us to get initial control of a problem area. Once we have the upper hand, we include other control measures and, over time, we turn problem areas into low-maintenance, desirable native plant communities. At that point, herbicide use is no longer needed.

As of 2002, we annually track our use of herbicides by pounds of active ingredient applied.

Reducing risk from herbicide use

We consider the potential risks to human health and the environment when selecting herbicides and monitoring our treated areas. If we find a herbicide has a negative effect on human health or the environment, we limit, phase out, or immediately stop using it.

See our table of Herbicides Approved for use on WSDOT Rights of Way (PDF 143KB) for herbicide safety measures and restrictions. We analyzed the risk from our roadside herbicide applications on the smallest likelihood of any potential exposures. Findings from these assessments show that most of the herbicides we use pose a low to very low potential risk to human and environmental health. In cases where we have found the potential risks were found to be anything above "low," we have limits on use to prevent causing harm.

Fact sheets: Herbicide toxicology and potential risks

Applying & regulating aquatic herbicides

Our crews avoid using herbicides in or along the edges of water whenever possible. They can treat sites such as retention/detention ponds and river banks during the dryer summer months to avoid the presence of water.


The National Pollution Discharge Elimination System (NPDES), through the Washington State Department of Ecology, regulates herbicide applications made in or over standing water.

The 2018 Noxious Weed Permit regulates the applications for control of aquatic weeds. It covers the indirect or accidental leakage of herbicides, adjuvants (an added chemical that improves the mix and effectiveness of the herbicide) and marker dyes into Washington waters, including estuaries, marine areas, wetlands, lake shorelines, rivers, streams and other wet areas.

We maintain statewide permits for all aquatic herbicide applications made on state highway property. The permits include public notification procedures and list the approved types of herbicides and surfactants (substances that help the herbicide "stick" to the plant). The permits cover herbicide applications by the maintenance workers and contractors working on state highway projects. All applications must be made by persons holding an aquatic certification on their pesticide applicator’s license. WSDOT is required to file annual reports on applications made under the permits. These permits are administered through the Washington State Department of Agriculture (WSDA).

Approving new herbicide products

We screen, evaluate and approve any new herbicides, or new formulations, based on their human health and environmental impacts before adding to our statewide contract and use on our rights of way.

Requests for herbicide review/evaluation

  1. Submit requests for review/evaluation to Headquarters Maintenance Office for consideration.
  2. An independent consultant analyzes and reports on potential risk associated with the product.
  3. The Headquarters Office reviews the formal risk assessment and decides whether or not to approve its use. If the product poses unacceptable risk, we do not include it on the contract and document the finding results.

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