Wisconsin aerial application operator and NAAA Government Relations Chairman Damon Reabe was in the Washington, D.C. area, this week to represent aerial applicators on the EPA’s Pesticide Program Dialogue Committee (PPDC).

The PPDC is an important federal advisory committee and a forum consisting of diverse stakeholders to provide feedback to the EPA’s Office of Pesticide Programs on various pesticide regulatory, policy and program implementation issues. Stakeholders include academia, state and local regulatory officials, environmental activists, grower groups and crop protection product manufacturers.

During the two-day meeting, Reabe gave a presentation to the committee regarding aerial application and UAVs, explaining many of the technologies advertised by UAV application are also available on manned aircraft. 

Reabe also explained how the EPA conducts a sophisticated spray drift risk assessment when registering a product for aerial use. The AgDrift

Reabe also explained how the EPA conducts a sophisticated spray drift risk assessment when registering a product for aerial use. The AgDrift model used for this predicts spray drift for fixed wing and single rotor applications. Other inputs into the model include weather conditions and boom length. These models do not necessarily apply to UAVs with two, four, six or more rotors. Reabe told the PPDC that without a similar model for unmanned aircraft, a proper spray drift risk assessment cannot be performed. Therefore, aerial pesticide labels should not apply to these unmanned aircraft until a proper drift assessment can be performed. 

Reabe closed by saying EPA and the registrants need to develop an AgDrift model to include multi-rotor aircraft. 

Other topics discussed at the PPDC included Farm Bill implementation and Hemp production, Biostimulants, and changes to the Pesticide Registration Improvement Act (PRIA). 

Following PPDC on Thursday, NAAA Executive Director Andrew D. Moore, Damon Reabe, and NAAA Coordinator of Government & Public Relations Frank Taylor met with several representatives from the U.S. EPA to discuss items related to aerial applications and pesticide re-registration. Topics included updating how the EPA models drift from aerial applications and the need to study UAVs in order to ensure safe and efficacious applications.

The conversation began with UAV’s, where many of the points from PPDC were discussed again. Jody Hemler from the FAA was present at the meeting to provide information to EPA on how the FAA hnadles UAVs being used for applications. EPA will be working to decide what they feel are the most important risk assessments to be conducted in terms of legalizing UAVs for pesticide applications.

As the meeting continued, conversation turned to AgDRIFT. Currently when the EPA evaluates a pesticide for registration or re-registration a model called AgDRIFT is used to predict the amount of drift from an aerial and other types of applications. This amount is then used with the toxicity and environmental impact profiles of the pesticides being evaluated to assess the risk to the environment and human health.

The model has several levels, or tiers, that allow more and more factors to be input into the model to see how they influence the amount of drift. The current risk assessments use the Tier 1 model, which only allows a few adjustments. The assumptions used with the Tier 1 model for aerial application are also not current industry standards or practices. These assumptions include the use of a fine-medium droplet size, not using a lowered spray boom, using a downwind swath displacement of only one-third of a swath width in a 10-mph crosswind, spraying in conditions right at the edge of being an inversion, and spraying over bare soil. The Tier 1 model also does not use a feature in AgDRIFT that changes wind direction if subsequent applications are made.

NAAA has commented many times to EPA on reregistration documents about the inaccuracy of these assumptions. More recently EPA has agreed to consider an alternative set of assumptions using a more advanced part of the model, Tier 3. These assumptions were discussed with the EPA on Thursday and include inputs for several variables that more accurately reflect how modern aerial applications are made.

First, NAAA proposes the aircraft modeled be changed from an AT-401 to an AT-502. The 2019 Operators survey shows that 81 percent of the agricultural aviation fleet in the U.S. is turbine powered, so using a turbine aircraft in the model is more realistic. For a droplet size, a medium droplet was suggested as opposed to a fine-medium. This was based on existing label requirements, nozzle selection surveys from PAASS, and observations from Operation S.A.F.E. fly-ins.

In order to reflect that fact that the vast majority of labels prohibit spraying during an inversion, NAAA recommended the atmospheric stability be set to reflect no inversion during the application. Instead of modeling over bare soil, a surface roughness more appropriate for a crop canopy was suggested, as most liquid aerial applications are post emergence, not pre-emergence. A boom drop of 24 inches with a length of 75 percent of wingspan was recommended for the boom configuration in the model. Finally, NAAA suggested that wind measurement height be set at 12 feet, a height appropriate for aerial application, as opposed to 6 feet, a height used for ground applications.

If EPA agrees with NAAA on the use of the Tier 3 model instead of the Tier 1 model as well as the new assumptions to be used with Tier 3, the estimated drift for aerial applications from AgDRIFT will be more realistic. This in turn will result in more accurate risk assessments for the environment and human health when aerial applications are reviewed during pesticide registration. 

A list of these proposals was presented to the EPA, who agreed to review them and let NAAA know their thoughts. If the agree with the use of the Tier 3 model with the updated assumptions, NAAA will formally request these changes through a letter.

In closing, Reabe asked if EPA would consider making the buffer zones on labels for treating next to water sources be wind directional. Since drift can not move upwind, it makes sense that any buffer zone be based on wind direction. EPA requested that NAAA include this request in the letter addressing the changes to AgDRIFT.

In addition to the proposed new tier and assumptions for AgDRIFT, UAVs were also discussed again, carrying forward the points Reabe brought up during his PPDC presentation.