Permit Still Needed to Exceed 25 PSI for Use Restricted Herbicides

Last summer, the Washington State Department of Agriculture proposed rule changes for Use Restricted Herbicides such as 2,4-D, 2,4-DB, 2,4-DP, MCPA, MCPP, MCPB, and dicamba. One of the proposed rule changes amended the 25 psi maximum nozzle pressure restriction when applying these “Use Restricted Herbicides”.

The proposed change recognizes the advancements in nozzle technology since the original rules were written, for example, air induction (AI) nozzles form larger droplets, which are less likely to drift than smaller droplets at higher pressures than older nozzle designs such as the flat fan nozzle.

Unfortunately, the proposed rule changes have not yet been approved, so the WSDA Pest Management Division has renewed a permit for applicators in Eastern Washington for 2018. The permit allows spray equipment to exceed the 25 psi nozzle pressure when using newer technology and equipment to create droplets in the course to very course range or larger – as defined by the American Society of Agricultural and Biological Engineers – to mitigate herbicide drift. Hopefully, the 2018 productions season will be the last one for which the permit will be needed.

For questions or comments, contact Drew Lyon by email at or by phone at 509-335-2961.
Washington State University