To minimize the risk to the environment, and human health, we carefully and selectively use herbicides on our roads and at the edges of water. This site also contains toxicology information sheets for each herbicide.
Both purpose and need
Our vegetation control activities include the use of herbicides, which are toxic substances to plants. We are aware of the potential dangers to both health and the environment that herbicides can pose, so our crews only use them when absolutely necessary.
We use herbicides to:
- When necessary, keep a strip of vegetation at the pavement’s edge.
- You can remove undesirable or unsafe plants.
Herbicides can be used to help control the problem area. Once we have the upperhand, we add other control measures. Over time, we transform problem areas into low-maintenance native plant communities. Then, herbicides no longer are necessary.
Since 2002, we have been tracking our herbicide use by the amount of active ingredient used.
Reduced risk from herbicide usage
When choosing herbicides and monitoring the areas we treat, we take into account the potential hazards to human health as well as the environment. We will immediately stop using a herbicide if it has a harmful effect on the environment or human well-being.
For more information about herbicide safety precautions and restrictions, see our table of approved herbicides for use on WSDOT Rights of Way. We calculated the risk associated with roadside herbicide applications based on the smallest possible exposure. These assessments showed that most herbicides we use pose a very low or very low risk to human health and the environment. We have established limits of use in cases where the potential risks are higher than “low”.
Fact sheets: Herbicide toxicology, potential risks
Aquatic herbicides: Application and regulation
Our crews do not use herbicides in or near the water’s edges. To avoid water, they can treat river banks and retention/detention pools during the dry summer months.
Through the Washington State Department of Ecology (NPDES), herbicide applications that are made in or above standing water are regulated by the National Pollution Discharge Elimination System.
The 2018 Noxious Weed Permit regulates applications for control. It covers the accidental or indirect leakage (or accidental) of herbicides and adjuvants (an extra chemical that improves mix and effectiveness of the herbicide), and marker dyes into Washington waters.
All aquatic herbicide applications on state highway property are subject to statewide permits. The permits provide public notification and list the approved herbicides and surfactants (substances which help the herbicide stick to the plant). The permits are for herbicide applications made by maintenance workers or contractors who work on state highway projects. All applications must come from persons who hold an aquatic certification on a pesticide applicators license. Annual reports are required by WSDOT for applications made under permits. These permits are administered by the Washington State Department of Agriculture.
New herbicide products approved
Before adding to our statewide contract or using our rights of way, we screen, evaluate, and approve any new herbicides or new formulations.
Requests for herbicide evaluation/review
- Send requests for review/evaluation in writing to the Headquarters Maintenance Office.
- A consultant independent analyzes and reports on the potential risk associated with the product.
- The Headquarters Office reviews the formal assessment and decides whether to approve its use. We will not include the product in the contract if it is deemed unacceptable. We will also document the findings.