DRONE APPLICATIONS
Optimizing drone spray performance for leafy greens
Connecting application settings, weather, and canopy measurements to understand drone spray coverage and uniformity.
Understanding where the spray goes
Drone applications offer new possibilities for leafy green production, but application performance depends on more than the amount of liquid delivered. Coverage, distribution across the flight path, and penetration into the crop canopy all matter.
Supported by the California Leafy Greens Research Program, this collaboration between UC Cooperative Extension and California State University, Monterey Bay (CSUMB) examines how flight speed, height, application volume, and weather affect spray performance.
Two connected stages
Stage 1 — Spray distribution and uniformity: completed. An array of water-sensitive cards measured spray patterns from an XAG P100H Pro drone across 12 combinations of flight height, speed, and application volume.
Stage 2 — Coverage within the lettuce canopy: in progress. Fluorescent dye measurements will examine deposition on upper, lower, and inner leaf surfaces to determine how the spray pattern translates into coverage within a real crop.
Findings from the Salinas Valley swath trial
The completed study included 36 flight passes and 1,152 collector-card observations. Application volume strongly influenced the amount and distribution of coverage measured on the cards.
Application volume and coverage
| Application volume | Mean card coverage | Core 90% spray width |
|---|---|---|
| 3 gal/acre | 2.86% | 23.5 ft |
| 5 gal/acre | 4.80% | 21.1 ft |
| 10 gal/acre | 10.18% | 20.5 ft |
Mean coverage at 10 gal/acre was approximately 3.5 times that at 3 gal/acre. However, the additional spray increased the central peak of the pattern rather than widening it. The core width containing 90% of the spray distribution became narrower as volume increased.
Flight settings
The highest treatment mean was 12.73% coverage at 10 ft, 12 mph, and 10 gal/acre. The lowest was 2.63% at 10 ft, 10 mph, and 3 gal/acre.
Across treatments, mean coverage was 6.65% at 12 mph and 5.24% at 10 mph. Flight height produced very similar means—5.98% at 10 ft and 5.92% at 14 ft—with no statistically significant difference reported between those heights.
Overlap and wind
Simulated effective swath widths ranged from 12.0 to 21.7 ft across treatment combinations when maintaining an overlap coefficient of variation of 25% or less. Settings that produced higher coverage could still require narrower pass spacing to achieve an even distribution. Coverage and uniformity therefore need to be considered together.
Crosswinds shifted the center of the measured spray pattern by −6.6 to +5.6 ft. Wind speed alone was a poor predictor of that displacement after accounting for operating settings. These measurements describe shifts in the collected spray pattern, rather than a measurement of off-target drift distance.
These findings report deposition on collector cards. They do not yet establish coverage within the lettuce canopy or biological control efficacy.
Next: measuring canopy penetration
A controlled-light imaging enclosure is being assembled and calibrated to photograph DayGlo Rocket Red fluorescent dye on lettuce leaves. The enclosure measures 55 inches wide, 36 inches deep, and 40 inches high and uses ultraviolet illumination and close-up photography.
Planned field trials in Yuma, Arizona, will extend the evaluation to lettuce canopy coverage, with research plots coordinated alongside UCCE biological efficacy evaluations. Together, the two stages will help connect application settings with the spray reaching the crop’s target surfaces.