Roadside spraying FAQs


Why does the County spray roadside shoulders?

Roadside spraying is a routine maintenance activity. It's performed every year to keep vegetation from encroaching onto the roadway and/or to prevent proper stormwater drainage.

Which roads get shoulder spraying?

About 850 shoulder miles of spraying are included in the County's Road Maintenance Program.

When is spraying performed?

Mid-spring is the most effective time for roadside shoulder spraying. Spraying is generally performed at night when there is little or no wind and impacts to the traveling public are minimized.

Who performs this work?

The County contracts with a private contractor for roadside shoulder spraying. The contractor is selected through a competitive bid process.

What rules govern roadside spraying?

State and federal herbicide application rules must be followed, including regulations by the Oregon Department of Agriculture. In addition, Washington County follows internal guidelines set forth within both the Integrated Vegetation Management Program (IVMP) and the Best Management Practices for Routine Road Maintenance.

How is spraying conducted?

A large tanker truck with a spray bar drives along the road, spraying the road edge. Roadside shoulders that are adequately maintained may not be sprayed. The county has taken these specific steps to minize environmental impacts: 

  • Spraying shall not be more than 3' from the edge of the road
  • Maintaining a spray buffer of 30' on either side of stream crossing, including bridges and culverts
  • Maintaining a spray buffer of 250' of streams with potential salmon or steelhead presence
  • Requiring the contractor use a computer-assisted delivery system to control mixture, application rate and placement of herbicides
  • Spraying at night to further reduce droplet drift potential and to minimize exposure to county residents
  • Limiting shoulder spraying to a portion of the paved roads Washington County maintains (of the 2500+ miles of road shoulder throughout the county, spraying is limited to approximately 850 miles)

What products are used?

Contractors use an approved mixture of:

  • Roundup Pro Concentrate (Glyphosate) - a broad spectrum spray
  • Opensight (Metsulfuron methyl) - a broad spectrum companion spray
  • EsplAnade 200 SC (Indaziflam) - a pre-emergent
  • Justified (modified seed oil) - a drift control and deposition aid that reduces unwanted drift by increasing droplet size

Is it possible to opt out of spraying?

Citizens can submit a No Spray Agreement if they don't want vegetation adjacent to their property sprayed:

Signs are available for purchase from Operations and Maintenance. Additional information about the online portal and the agreement is available on the Right-of-Way Permits page.

For more information call (503) 846-ROAD (846-7623) or email