—by Matt Milkovich
Even those on the cutting edge of using drones as sprayers find it hard to keep up with all the emerging technologies.
Starting as an integrated pest management educator and now a viticulture specialist, Mike Reinke of Michigan State University has been testing spray, or applicator, drones on grapes and other specialty crops since 2022. In those few years, the technology has advanced at a head-spinning pace.
“We’re just now getting to the phase where people are keeping drones more than one year,” he said.
Reinke’s latest model is an XAG P100 Pro, on loan from Pegasus Robotics, the importer for Chinese drone manufacturer XAG.
Reinke spent the first couple of years evaluating drone spray coverage on different canopies, including grapes and apples, at research and commercial farms. He held efficacy trials on grapes in 2024. His drone work has been funded by the U.S. Department of Agriculture’s Specialty Crop Block Grant Program, the Michigan State Horticultural Society and Michigan Cherry Committee.
So far, drone spray efficacy has been comparable to ground sprayers.
“There was no fundamental difference as far as control of diseases and insects,” Reinke said.
He recommends drone sprayers for certain applications, including targeted sprays or perimeter sprays.
“I don’t see drones as a wholesale replacement for ground sprayers,” Reinke said. “Drones are not a silver bullet. They’re a new tool, depending on the need.”
Spray drones range in size from 3 feet to 10 feet across, can weigh up to 200 pounds and carry up to 18 gallons of liquid (the P100 Pro holds 15 gallons). Tubes from the spray tank housed underneath the drone lead to emitters. Older drones used the same kind of nozzles found on an airblast sprayer, but more recent drones have rotary atomizers, which can change flow rate and droplet size without having to change nozzles, he said.
Reinke described the flying machines as mostly autonomous; the operator preplans the flight and, if everything goes right, never has to manipulate the drone while it’s airborne.
The newness of drone spraying makes the economics difficult to evaluate. As the industry matures, more robust economic analyses will be possible. But during a trial at MSU’s Southwest Michigan Research and Extension Center last year, it took a tractor operator 5.2 hours to make eight pesticide applications on a 2.5-acre field. A drone performed the same function in 3.4 hours, he said.
Reinke and MSU entomologist Rufus Isaacs studied spray drone effects on grape berry moth, a troublesome vineyard pest in Michigan. Grape berry moth tends to build up populations and migrate into vineyards just before harvest, after most pesticide sprays have already been made, Isaacs said.
The researchers conducted trials at two commercial juice-grape vineyards for two seasons. The drones were used to spray vineyard perimeters late in the season, with the goal of preventing grape berry moth from entering. The drones provided thorough canopy coverage, and there was no real difference in efficacy compared to ground sprayers, Reinke said.
Isaacs was encouraged by the drone’s performance. Making border applications with drones could be an efficient way to treat grape berry moth late in the season, as opposed to unlimbering a sprayer that was hoped to be done for the year, but there’s still a lot to learn about product selection, spray timing and logistics, he said.
After conducting drone spray coverage demonstrations on high-density apple canopies and low-density sweet cherry and pear blocks at MSU’s West Central Michigan Research and Extension Center last year, MSU tree fruit educator Emily Lavely agreed that drones might work best for spot spraying or targeting specific areas. They are fast, maneuverable and can deliver the right concentration of material where needed.
But she also said a lot of questions still need to be answered. How high should the drone fly above the canopy? What’s the most efficient speed and flight pattern? How should drone operators approach a low-density pear block versus a high-density apple block?
MSU researchers plan to use a spray drone on a low-density tart cherry block this year to target cherry leaf spot in the tops of the canopies.
It can be difficult for airblast sprayers to reach the tops of bigger tart cherry trees, and unchecked cherry leaf spot infections tend to move down the canopy from the top. Drone sprays targeting treetops from above might be a tool growers could use to address that particular problem, Lavely said. •
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