How do you control diseases in cornfields where conventional aerial fungicide applications are difficult or impossible, and ground equipment isn’t available? As recently as three years ago, the answer was selecting the most disease-resistant hybrid available, because there weren’t any other options. Enter drones — could they be a viable option for applying fungicides in these situations?

Kiersten Wise, Extension plant pathologist at the University of Kentucky, who formerly held the same position at Purdue University, explored the possibility beginning in 2019. Three UK Extension county agents in adjoining Adair, Taylor and Green counties in south-central Kentucky worked with farmers to carry out field-scale fungicide application trials with drones.

“The No. 1 goal was to determine if we could get good efficacy ― good control of a disease like gray leaf spot ― using a drone application system,” Wise explains. “Our results from 2019 are proof of concept. Using water-sensitive paper, we confirmed that we were getting adequate coverage with the drone application on the ear leaf and above. The important thing at the VT stage and after is to control disease on the ear leaf and those above it ― those are the leaves that primarily absorb sunlight and contribute to yield at that point in the season.”

Devil in the details

While Wise, the agents and farmers proved that application by a drone can halt disease, there are still tradeoffs to consider before deciding that drone application might fit on your farm.

“In two of the three counties in 2019, yield increases were small, but disease pressure was also low,” Wise observes. Counting the cost of fungicide and application costs, the farmers didn’t break even, and would not have broken even no matter the application method. In Taylor County, Ky., in 2019, however, disease pressure was considerably higher, and the yield increase was over 20 bushels per acre, netting a sizable profit. In fact, the farmer hired the commercial applicator to spray his fields with a drone in 2020.

“We have always found that if disease pressure is low, the yield increase will be smaller,” Wise says. “That has held true no matter how you’re applying fungicide.”

Wise notes that the commercial applicator working with them in 2019 was efficient, and there were few problems with the drone. It was equipped with a 15-foot spray boom.

They attempted to repeat the fungicide trial in 2020, using a different applicator with a different drone. Because the operator encountered several problems with breakdowns, including waiting for a part for two weeks, Wise scrubbed the test in 2020.

Reliability, including access to parts, is critical, she says. Some farmers have considered buying their own drone and applying themselves. “You would need to consider things like how much time it would take for marking field boundaries and the application itself,” she says. “Also think about added equipment cost, including batteries, battery chargers, barrels and pumps for water storage and equipment for pre-mixing pesticides. Additional insurance policies may be needed, too.” Plus, if you’re doing your own spraying by drone, you need to obtain your FAA license, she notes.

“We’ve shown that it’s an option, especially in fields where it’s hard to spray any other way,” Wise says. “There are logistics to consider. We’ll keep looking at it.”