The Big Picture: Spraying Less, Saving More
Spray drones are one of the hottest new technologies in agriculture. They promise precision, flexibility, and less soil compaction—but do they really match the performance of traditional sprayers?
To find out, Missouri researchers put the DJI Agras T40 drone to the test in soybean fields across the state. Over two years, they compared drone spraying with standard ground rigs, experimenting with spray speed, height, and volume to see how drones stack up.
The results? Drones can control weeds under the right conditions, but ground rigs still provide more consistent coverage and weed control.
Project Overview
Sprayer drones are capturing attention across farm country, but new research from the University of Missouri shows they may not yet be ready to replace traditional ground rigs when it comes to weed control.
Led by Kevin Bradley, a weed science professor at Mizzou, the study tested DJI Agras T40 unmanned aerial vehicles (UAVs) in side-by-side trials with ground-based sprayers during the 2023 and 2024 growing seasons. The team looked at spray coverage, off-target drift, droplet size, and overall weed control in soybean fields.
The results were mixed. Ground sprayers consistently delivered more uniform coverage and bigger spray droplets, which translated into steadier weed control. UAV applications, while showing promise, often produced smaller droplets and patchier coverage — especially at the edges of swaths. That created variability in managing waterhemp, one of Missouri’s most stubborn weeds.
Still, the research highlighted important opportunities. Adjusting speed, spray height, and volume helped improve drone performance. At 8 miles per hour and 10 feet above the canopy, for example, drones provided better coverage than at higher speeds or heights. Increasing spray volume from 3 to 6 gallons per acre also improved consistency.
Notably, the drones achieved similar levels of spray penetration into the soybean canopy as ground sprayers, suggesting UAVs may eventually become competitive for certain applications. The ability to target weed escapes with drones could cut down on total herbicide applied, lowering costs and reducing environmental impact.
“This isn’t about saying drones can’t work — it’s about understanding how to make them work better,” Bradley said. “If we manage factors like droplet size, swath width, and application speed, the technology can get closer to delivering the kind of results farmers expect from ground sprayers.”
Herbicide-resistant weeds remain a top challenge in Missouri soybean fields, and farmers are eager for tools that can save time and reduce labor. Drones may not fully replace ground rigs yet, but Bradley believes rapid improvements in technology will push the industry forward.
Next steps include testing pre-emergence herbicides, evaluating adjuvants, and comparing different drone platforms. As one grower who attended a field day put it: “Drones may not be the silver bullet today, but it’s only a matter of time before they become part of our weed control toolbox.”
What We Learned
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Ground Rigs Outperform Drones in Coverage
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Ground sprayers covered 2–3x more area and produced larger droplets, leading to more uniform weed control.
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Drone droplets were much smaller, which increases risk of drift.
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Drones Can Work—With Adjustments
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Best results came with lower speeds (8 mph) and lower spray heights (10 feet).
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Using higher spray volumes (6 gallons/acre vs 3 GPA) improved coverage and control.
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Similar Canopy Penetration
Despite less spray volume, drones were able to penetrate the soybean canopy about as well as ground rigs. -
Waterhemp Control Possible, But Patchy
At certain flight paths, drones achieved similar weed control to sprayers. But gaps at the edges of drone passes reduced effectiveness.
Why It Matters for Missouri Farmers
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Opens the Door to New Options: While drones aren’t yet a one-to-one replacement, they may play a role in targeted spraying of weed patches or difficult-to-reach areas.
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Helps Manage Resistant Weeds: As herbicide-resistant waterhemp and other weeds spread, new tools will be needed.
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Could Reduce Herbicide Use in the Future: If drone spraying becomes more precise, farmers could use less product overall, which may bring both economic and environmental benefits.
What’s Next
This project showed that drones aren’t ready to fully replace sprayers, but technology is improving fast. Future research will test:
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How drones perform with pre-emergence herbicides.
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How different adjuvants (tank additives) affect spray performance.
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How different drone platforms compare to each other.
With the right adjustments, spray drones could become an important part of soybean weed management.