Andrew Moore, Executive Director of the National Agricultural Aviation Association, issues a response from the NAAA on a recent article published by CropLife Magazine about drone spraying in Iowa. Below is Moore’s letter, which was published on the CropLife Magazine website here.

Dear Crop Life Media Group,

On behalf of members of the National Agricultural Aviation Association (NAAA), I am writing to inform you the July 11 article “Rantizo Approved for Agricultural Drone Spraying in Iowa” written by CropLife staff lacked some vital information about manned aerial application operations. It is indeed exciting to think about the many benefits of treating crops by air instead of by ground. Superior coverage, the ability to make applications even if the soil is wet, and the lack of destruction to the crop caused by driving through it are just some of the benefits from aerial application. While growers might be excited about the potential use of UAV’s for making aerial applications, they need to be reminded that manned agricultural aircraft have been providing this service to growers for almost a century and remain readily available to treat large acreages of crops throughout the nation immediately.

The article is correct to state abnormally wet weather conditions across the Midwest make aerial application an indispensable tool for ensuring high yields. However, the article does not state that the UAV used by Rantizo, the DJI Agras, can spray only 7-10 acres an hour. During a 10-hour day of applications, this equates to only 70 to 100 acres treated per UAV. USDA estimates that the average farm size in the U.S. is 444 acres and the most important principle in combatting a pest is to eradicate it immediately before it spreads. A single manned aircraft can spray upwards of 2,000n acres a day. This is one of the benefits of manned aerial application that is unmatched by current UAV technology. In future articles we feel it is vital to include this information, so readers have an accurate basis for comparing the two application methods.

It is, of course, possible to use multiple UAVs to spray a single field, however that would require licensed UAV pilots unless specifically granted an exemption by the FAA to allow one remote pilot to operate multiple UAVs. Even then, each UAV would require being loaded individually. Manned agricultural aircraft have hopper capacities up to 800 gallons. At a rate of two gallons of spray per acre, a single load from an agricultural aircraft with an 800-gallon hopper can treat 400 acres. The capabilities of modern
agricultural aircraft allow the manned aerial application industry to treat approximately 127 million acres
of cropland annually.

Furthermore, it still is not clear from a regulatory standpoint if existing pesticide labels allow for UAVs to make aerial applications. When EPA registers a pesticide product for aerial use, it conducts spray drift risk assessments using the AgDRIFTTM model. This model predicts spray drift for only single propeller fixed-wing and single rotor aircraft applications. Several other inputs are plugged into the model as well,
including weather conditions and boom length. However, these models do not apply to UAVs with two, four, six or in the case of the DJI Agras, eight rotors. The model also doesn’t apply to the lighter weight characteristics of a small UAV that doesn’t have the higher air pressure wake to push the applied material deep into a crop’s canopy. Without similar models for the various types and sizes of UAVs a proper spray drift risk assessment cannot be performed. Some of the initial testing of UAV’s using drift prediction models (as Published in Volume 61 of the Transactions of the ASABE) indicates that application quality markedly decreases and drift potential increases when the UAV’s are operated above an average speed of 12 mph.
Modern agricultural aviators have fine-tuned the use of technology to make effective and safe applications. They use droplet size models available from the USDA-ARS Aerial Application Technology
Research Unit to set up their aircraft to provide the exact droplet size required by the pesticide label. They can test pattern uniformity and droplet size at Operation S.A.F.E. Fly-in clinics. Agricultural aircraft have differentially corrected GPS capable of determining the aircraft’s position 20 times per second with an accuracy of less than 1 foot. Just like modern ground rigs, they have flow control systems that ensure the targeted application rate is applied uniformly across the field and allow them to make precision/variable rate applications.

Aerial applicators have the ability to monitor weather conditions in the cockpit. A smoker injects a small amount of vegetable oil into the aircraft exhaust system that creates smoke, allowing the pilot to determine, by observing smoke movement, the wind direction and an estimate of wind speed. Inversions can be detected by observing vertical smoke movement. The Aircraft Integrated Meteorological Measurement System (AIMMS) provides real-time onboard weather data, including wind speed and direction, temperature, and humidity. Pulse width modulation nozzle control technology is now available for agricultural aircraft as well.

NAAA agrees that aerial application is indeed the superior way to treat crops for a variety of reasons. We do feel, however, that growers need to be aware of the capabilities of manned agricultural aircraft in addition to learning about emerging UAV technologies, and their fallbacks. Only the manned aerial application industry has and will continue to treat 127 million acres of cropland in the U.S. this growing season.


Anderw D, Moore, Executive Director

National Agricultural Aviation Association