Last week NAAA submitted a letter to EPA Administrator Andrew Wheeler. The purpose of the letter was to urge the EPA to promptly evaluate UAS’ ability to make safe and precise and efficacious applications of pesticides, similarly to how other forms of application—ground, air-blast and single rotor and single propellered manned aircraft—were evaluated and tested in each pesticide active ingredient evaluation. UAS, in some instances, are now being used for making small-scale aerial applications, yet without being tested and modeled to determine drift potential.

Manned agricultural aircraft, along with ground rigs and airblast sprayers, have all been evaluated in extensive field studies, many as part of the Spray Drift Task Force project, and the data collected is used in the AgDRIFT model. For aerial application, the model allows for a variety of variables to be examined, including aircraft properties, boom and nozzle configuration, and wind speed. While EPA typically uses the Tier 1 assumptions when running AgDRIFT, which uses an AT-401 with specific setup parameters, they do have the ability to change variables and explore alternatives. As an example, AgDRIFT was used to verify reducing boom length reduces drift. This helped secure 15 mph wind speed limits for many pesticides during their registration review process.

AgDRIFT is used in the pesticide registration and registration review processes to model the amount of drift from aerial and other forms of applications. The estimated amounts of drift are then used in the human health and ecological risk assessments. In turn, these risk assessments are used to determine if a pesticide will be approved, what application methods can be used to apply it, and what restrictions need to be placed on the label. NAAA pointed out that because no UAS are currently modeled in AgDRIFT, it is currently impossible to evaluate the risk from making an aerial application with a UAS. Without proper risk assessments, it is impossible to know how safely and accurately aerial applications with UAS are.

Many consider UAS to be an aerial application and thus already an approved application platform for any pesticide with an aerial label. However, NAAA pointed out in the letter to Administrator Wheeler that there are considerable differences between UAS and manned agricultural aircraft. One critical difference is weight. Most UAS being marketed for making aerial applications are much lighter than manned agricultural aircraft. Weight affects the strength of an aircraft’s wake, which is what pushes the spray down and out from the aircraft and into the plant canopy. Lighter aircraft do not have as strong of wakes, which will affect their efficacy and drift potential.

Another key difference between most UAS and manned aircraft are the number of rotors used. While helicopters utilize a single rotor, UAS commonly have multiple rotors which is expected to have a significant impact on vortices generated by the aircraft. In terms of current label restrictions about boom length relative to wingspan or rotor diameter, there is no data if these restrictions are appropriate for multi-rotor UAS. NAAA verified the uncertainty surrounding the accuracy of UAS applications with current research published in the Transactions of the ASABE (American Society of Agricultural and Biological Engineers).

NAAA pointed out several other differences, including that the UAS certification process is not nearly as rigorous and UAS pilots do not have to have a commercial pilot’s license. PAASS and Operation S.A.F.E. were described in the letter to demonstrate to the EPA the dedication and professionalism of the agricultural aviation industry. NAAA also reminded Administrator Wheeler that Canada’s Pest Management Regulatory Agency (PMRA) has already determined that the use of UAS to apply pesticides is not permitted until UAS testing has been completed.