After years of effort, the EPA has accepted the National Agricultural Aviation Association’s (NAAA) recommendations to improve the accuracy of the models used to estimate the amount of drift from aerial applications.
Until the recently released Insecticide Strategy (IS), EPA had used the Tier 1 model in AgDRIFT, which had many outdated assumptions that led to unrealistic aerial drift estimates, such as the typical droplet size used, aircraft type reflecting the industry, weather conditions during the application, and boom drop.
Because of this, there have been decades of pesticide registration risk assessments and decisions that have overstated the risk of aerial application.
NAAA submitted a letter to EPA in June of 2020 outlining recommended changes in the assumptions that should be used in the Tier 3 AgDRIFT model. Prior to that letter, NAAA has included the recommendations on numerous comments to EPA.
EPA used the Tier 3 AgDRIFT model in the IS and included most of NAAA’s suggested assumptions for the variables within the model.
EPA changed the default aircraft from an AT-401 to an AT-802 with a corresponding increase in swath width and decrease in the number of passes. The default droplet size was increased to medium, and the atmospheric stability was set to a level that rules out the presence of an inversion. EPA also changed the height at which wind speed is measured to reflect smokers and onboard meteorological measurement systems and increased the upwind swath displacement to reflect what is actually practiced in the industry.
There were two assumptions EPA did not agree with completely on with NAAA – surface roughness and standard boom drop. NAAA plans to conduct additional data collection and analysis to better support our positions in a future follow up letter to EPA on these two variables.
With EPA’s change to the Tier 3 model, the estimated drift from aerial applications has been substantially reduced. This will make it far easier for pesticide registrants to label their products for aerial applications, ensuring ag aviation industry’s customers can continue to rely on the aerial application of products to protect their crops.
