In my previous blog, I mentioned that drone configurations are not standardized and that credible, replicated studies continue to be conducted to determine the most optimum drone design parameters to minimize drift and maximize deposition and spray coverage on the target.  

In 2023, Dr. Darcy Telenko, an associate professor with Purdue University Extension, conducted research funded by the Indiana Soybean Alliance on drone-applied fungicides to reduce soybean foliar diseases. Her main goal was to determine whether drones could achieve the fungicide coverage needed to manage or mitigate the following soybean diseases: frogeye leaf spot, septoria brown spot, and cercospora leaf blight. She also compared the drone application to traditional on-the-ground fungicide application to see which provided the best efficacy. 

Telenko’s research was conducted at three Purdue research farm plots. They compared a 2- and 5-gallon per acre rate from a UAV to a 20 gallon per acre rate with a ground rig. All were applied at both R3 and R5 soybean growth stages. There was also a non-treated soybean plot included for comparison.  

Because disease pressure was low in 2023, they focused on spray canopy penetration, spray width and droplet distribution. Soybean yield was similar across all plots. After one year of research, Telenko concluded that drone applications performed as well as the ground rig in reducing frogeye leaf spot at both soybean growth stages of R3 and R5. However, when comparing disease percentage, the drones appeared to be better at controlling septoria brown spot than the ground-rig, but the differences were not significantly different. The drone’s 2-and 5-gallon carrier volume amounts were both similar in the success of controlling disease. 

Credit: Soybean Research and Information Network, July 8, 2024.

Successful Drone (UAV) Pesticide Application Tips 

One of the most important best practices is knowing the effective spray swath width. However, no formula currently exists to determine this while accounting for wide variations in nozzle choices and their physical configurations, flying speed, wind direction, and wind speed. The best way to determine swath width is by using food-grade coloring to observe variations of spray pattern and droplet size across a strip of paper tape. 

Flight altitude must be chosen carefully because high altitude can expose droplets to weather conditions such as wind, relative humidity, and temperature. This increases the potential  for droplet drift, especially as droplets become smaller, with many failing to reach the target under conditions of low relative humidity and high temperatures.  

Changes in flight altitude and/or the distance between each pass should be made to provide a more uniform distribution of droplets. The flight altitude also is significant because of the role it plays in the quality of spray deposition into the target canopy, and the pesticide coverage (number of droplets per square inch) on the canopy.  

Normally, you should increase the gallons per acre application rate by using a nozzle that has a higher flow rate capacity (gallons per minute) or by flying at a slower speed; however, this is not viable option when using spray drones because frequent tank refills and battery replacement will be needed. To improve spray deposition and coverage, nozzles that produce small droplets (not fine or very fine category) should be used.  

In the study reference above, Telenko used the DJI Agras T30 Drone. One of the key takeaways is that you should use a drone that allows you to switch out the nozzles if needed to achieve the most accurate spray width and droplet size to aid in fungicide efficacy.  

Resources:  

Drones for Spraying Pesticides—Opportunities and Challenges | Ohioline 

Can Fungicide Applications via Drones Effectively Control Soybean Foliar Diseases? – Research Highlight – Soybean Research & Information Network – SRIN