Herbicides are efficient and effective tools for vegetation management and weed control. However, WSDOT recognizes there may be potential impacts to health and the environment, and minimizes herbicide use wherever possible. We uses herbicides two ways:
- to maintain a vegetation-free strip at the edge of the pavement where necessary
- to selectively control and eliminate undesirable plants
Historically, about 60 percent of the herbicides used by the agency were for annual maintenance of a vegetation-free strip at the edge of pavement. WSDOT is currently studying alternatives to this practice to determine the most appropriate and cost effective methods for varying roadsides around the state.
For herbicides used to control weeds and other unwanted plants, We follow a process that helps ensure herbicides are used appropriately and only when necessary in combination with other effective control measures. The ultimate goal in any treatment is to replace unwanted vegetation with appropriate native plants. In many cases herbicides are an effective tool for initial control of a problem. When combined with other control measures, herbicide use can be minimized or eliminated over time.
WSDOT has been tracking its herbicide use trends in detail since 2002. Herbicide use is reported annually by pounds of active ingredient applied. This information is available to the public. To obtain a copy please e-mail willarr@wsdot.wa.gov .
Minimizing Risk from Herbicide Use
Two important factors in herbicide selection and application are potential risks to human health and the environment. It is oue policy that any herbicide used on state highway right of way be screened through a scientific risk assessment specific to application rates and methods used by the agency. If certain herbicides are found to have a potential for higher toxicity to human health or the environment, their use on state highway roadsides may be limited, phased out, or immediately eliminated.
In 1993, We completed a toxicological analysis and risk assessment for herbicides used in the roadside vegetation management program. In 2003 and 2005 a consultant updated the information for the agency based on the current use and any new scientific findings. This updated analysis now considers all herbicides and applications methods currently employed by the agency.
Analysis of risk was based on very conservative assumptions of any potential exposures from WSDOT roadside applications. Findings from these assessments indicate that for most herbicides in most situations, WSDOT’s use of herbicides pose a low to very low potential risk to human and environmental health. In cases where the potential risks were calculated to be above low, We have placed limitations on use to further minimize potential for exposure. The table Herbicides Approved for use on WSDOT Rights of Way (pdf 55kb)outlines the use for individual herbicide including precautions and restrictions were they apply. Fact sheets summarizing the toxicology and potential risks for the individual herbicides used by WSDOT can be viewed below.
Contact Ray Willard for additional herbicide use analysis and risk assessment documentation.
Introduction - 2003/2005 Supplement to the 1993 Vegetation Management EIS, Appendix B.
Chapter 1 - Herbicide Active Ingredient Properties (pdf 56kb)
Chapter 2 - Wildlife Risk Assessment (pdf 592kb)
Chapter 3 - Aquatic Risk Assessment (pdf 520kb)
Chapter 4 - Human Health Risk Assessment (pdf 608kb)
Chapter 5 - Toxicological Data Summaries (pdf 372kb)
WSDOT Policy for Approval and Use of Any New Herbicide Products
Any new herbicides or formulations of existing herbicides that become available and have potential for use in roadside vegetation management will be screened, evaluated and approved based on the following procedures:
All new pesticide products that may be used for roadside vegetation management by the WSDOT will be formally evaluated for environmental and human health impacts prior to addition to the statewide contract and use on WSDOT rights of way. No pesticide products will be used on WSDOT right-of-way without approval through the process as described below.
Submit request for review/evaluation to the Headquarters Maintenance Office .
If warranted, an internal evaluation will be conducted by the Headquarters Maintenance Office to determine if a formal risk assessment is needed.
If a formal risk assessment is determined necessary, the product will be referred to an independent consultant for analysis and report on potential risk associated with the product.
The Headquarters Maintenance Office will review the formal risk assessment and a determination regarding use will be made. If the product is approved for use, the product will be added to the state contract. If the product poses unacceptable risk it will not be included on the contract and the results of findings will be documented.