Contributed by Joel Felix, Oregon State University, September 2023.
When I picked the ‘drone spraying’ topic for this week’s article, the idea drew my attention to useful information I had been curious about. Do you know how long aerial agricultural pesticide spray has been in existence? You do? If you do not but had been curious about it, I am with you. It turns out that just like civil aviation, ag pesticide application has roots to Ohio. An account of the first pesticide application test flight is retold in an article commemorating 100 years of agricultural aviation (Agricultural Aviation: Spring 2021 and available online at Agricultural Aviation Spring 2021.
Briefly, in response to expanding ag acreage and to control insects ravaging cotton in the south, two entomologists, C. R. Nelly and J. S. House at the Ohio Agricultural Experiment Station, set out to run the first ever aerial spray experiment. So, in 1921, the two recruited a U.S. Army pilot named Lt. John A. Macready to man the aircraft. He piloted an aircraft carrying 175 lbs of an insecticide and dusted trees in 54 seconds! That, ladies and gentlemen, set off the first aerial application of insecticides to control insects in the southern cotton fields starting in 1922. As they say, the rest is history!
Since that time, aerial pesticide spray has evolved in ways few could have imagined back in the early 1920s. Fast forward to 2023 and you find a multitude of aerial pesticide application equipment from fixed-wing aircrafts and helicopters to Unmanned Aerial Vehicles (UAV), also known as Unmanned Aerial Systems (UAS), and commonly referred to as ‘Drones’. Small, remotely piloted aircraft are being used to apply pesticides around the world; with 30% of all agricultural spraying in South Korea and about 40% of Japan’s rice crop sprayed using drones (Erdan Ozkan, 2023).
Erdan Ozkan (2023) has identified four reasons that make drones attractive in agriculture: 1) topography or soil conditions that prevent use of traditional ground sprayers, 2) when aircraft and helicopters are too expensive to use, 3) when spraying small irregular shaped fields, and 4) drones significantly reduce the risk of applicator being contaminated by pesticides. I would add the possibility of spraying areas not easily accessible by ground rigs or other aerial equipment.
What does it take to become a drone pesticide applicator? In Oregon, (maybe in other states as well) there are requirements beyond other license types. One has to hold an active Oregon commercial, public, or private applicator license; hold a valid FAA commercial airman’s certificate for the type of aerial equipment being used; provide a current FAA medical certificate; provide documented proof of at least 50 hours of pesticide application flight time. Recertification credits are required as well.
In March 2023, a local commercial drone pesticide applicator visited the Malheur Experiment Station to demonstrate the capabilities drones have to offer. The equipment is rigged on a trailer that is pulled by a pickup truck (Figure 1).
Figure 1. A trailer-rig including a DJI AGRAS T40 drone fitted with a 10.56-gallon (40 liters) tank, water tank, pesticide/water mixing tank, power generator, battery charger, and a pump. Photo by Joel Felix, Oregon State University 2023.
The demo involved a DJI AGRAS T40 drone equipped with a 10.56-gal (40 L) tank and fitted with two nozzles (one each on the two rear-end propellers), called a ‘dual atomized spraying system’. Using the intelligent route mode in the provided DJI software, the operator develops a flight plan for a particular field and the drone once deployed executes that plan flawlessly. Operated at a 10-ft flight height, it is capable of delivering a 30-ft spray swath, thanks to the automizer disks that generate fine droplets as needed (Figure 2).
Figure 2. DJI ACRAS T40 drone in action. Photo by Joel Felix, Oregon State University 2023.
The drone field delivery is communicated and monitored in real-time on the remote controller screen, displaying speed, solution spray volume (GPA), gallon/minute, and a host of other information. Spraying at 2-3 gallons/acre (using a 10.56-gal tank) requires multiple tank refills to cover one field spray job. So, once the drone senses an empty tank or when summoned by the operator, it stops spraying and returns to the base station. Once it lands, the operator refills the tank and swaps out the battery (if needed) and the drone is redeployed to continue spraying, all in under one minute! Thanks to the satellite communication, the drone starts exactly at the same spot it left off during the earlier run!
In my observation, drone pesticide spray is convenient and probably suited for much more forgiving pesticides, for example, insecticides and fungicides, but risky for herbicides, particularly if there are sensitive crops nearby. Also, the turbulence generated by propellers could aid fungicide/insecticide delivery in vineyards, orchards, and other crops where pesticide penetration into the canopy is desired. For herbicides, however, spraying at such low gallonage could result in product drift to cause injury onto sensitive crops. I will write a follow-up article next time regarding my observations.
References for further reading.
Erdal Ozkan. 2023. Drones for Spraying Pesticides—Opportunities and Challenges. FABE-540 The Ohio State University.
Randy Hardy, 2021. The WWII aircraft played a vital role in ag aviation’s 100-year history. Agricultural Aviation: Spring 2021 48 (2): 18-26 and available online