Field trials were conducted to evaluate the efficacy of agricultural drones in controlling Spodoptera exigua infestations within soybean-corn strip intercropping systems. Two commercial agricultural UAVs—designated as UAV-A (featuring a dual-disc cold-atomization nozzle system) and UAV-B (equipped with centrifugal nozzles)—were deployed under varying operational parameters. Spray solutions contained lure red tracer mixed with broflanilide (100 g/L SC) and lufenuron (10% SC) at an 8:2 ratio. The experimental design assessed droplet deposition patterns, pest control efficacy, and crop safety across multiple parameters.
Operational Parameters and Methodology
Trials were arranged in a randomized block design with eight treatment zones and one untreated control. Key operational parameters for the agricultural UAVs included:
| Treatment | UAV Type | Height Above Canopy (m) | Spray Volume (L/ha) | Pesticide Dosage (% of standard) |
|---|---|---|---|---|
| T1 | UAV-A | 2.5 | 45 | 100 |
| T2 | UAV-A | 1.5 | 45 | 100 |
| T3 | UAV-A | 2.5 | 45 | 70 |
| T4 | UAV-A | 2.5 | 30 | 100 |
| T5 | UAV-B | 2.5 | 45 | 100 |
| T6 | UAV-B | 1.5 | 45 | 100 |
| T7 | UAV-B | 2.5 | 45 | 70 |
| T8 | UAV-B | 2.5 | 30 | 100 |
Droplet deposition was quantified using water-sensitive papers positioned at upper, middle, and lower canopy strata (n=9 per treatment). Deposition density (droplets/cm²) and coverage (%) were calculated using:
$$ \text{Deposition Density} = \frac{\text{Total Droplets}}{\text{Paper Area (cm}^2\text{)}} $$
$$ \text{Coverage} = \frac{\text{Pixels Covered by Droplets}}{\text{Total Pixels}} \times 100\% $$
Control efficacy was determined through larval mortality counts pre-treatment and at 1, 3, and 7 days post-application:
$$ \text{Mortality Rate} = \left(1 – \frac{\text{Post-treatment Larvae}}{\text{Pre-treatment Larvae}}\right) \times 100\% $$
$$ \text{Control Efficacy} = \left(1 – \frac{\text{Mortality}_{\text{Untreated}}}{\text{Mortality}_{\text{Treated}}}\right) \times 100\% $$
Droplet Deposition Characteristics
UAV-A generated significantly finer droplets (volumetric median diameter: 50-150 µm) versus UAV-B (80-250 µm). This directly influenced canopy penetration and deposition uniformity. UAV-A’s dual-stage atomization system enhanced deposition in lower canopy strata and leaf undersides—critical for targeting Spodoptera exigua larvae.
| Treatment | Deposition Density (droplets/cm²) | ||
|---|---|---|---|
| Upper Canopy | Middle Canopy | Lower Canopy | |
| T1 | 64.7 ± 3.2 | 58.3 ± 2.8 | 81.9 ± 4.1 |
| T2 | 11.5 ± 0.9 | 13.8 ± 1.1 | 9.9 ± 0.8 |
| T5 | 27.0 ± 1.5 | 11.8 ± 0.7 | 4.2 ± 0.3 |
| T6 | 18.2 ± 1.2 | 15.1 ± 1.0 | 12.7 ± 0.9 |
Lowering UAV-A’s height to 1.5m (T2) reduced deposition density by 76-88% due to rotor downwash displacing foliage. UAV-B achieved maximal coverage (7.7%) on leaf surfaces at 1.5m height but exhibited poor underside deposition. Optimal parameters were:
- UAV-A: 2.5m height, 45 L/ha spray volume
- UAV-B: 1.5m height, 45 L/ha spray volume
Pest Control Efficacy
Both agricultural drones achieved >92% control efficacy by day 7 across all treatments. UAV-A at optimal parameters (T1) demonstrated near-complete elimination (99.8%). UAV-B required higher spray volumes to compensate for inferior canopy penetration.
| Treatment | Day 1 Efficacy (%) | Day 3 Efficacy (%) | Day 7 Efficacy (%) |
|---|---|---|---|
| T1 | 78.1 ± 2.5 | 97.2 ± 0.8 | 99.8 ± 0.1 |
| T3 | 85.0 ± 1.8 | 96.5 ± 0.9 | 98.3 ± 0.4 |
| T5 | 84.9 ± 1.9 | 95.1 ± 1.0 | 96.5 ± 0.7 |
| T6 | 91.3 ± 1.2 | 87.6 ± 1.5 | 92.0 ± 1.1 |
Crop Safety and Environmental Considerations
Phytotoxicity was minimal across treatments. Only reduced-volume applications (T4, T8) and UAV-A with 30% pesticide reduction (T3) exhibited Grade 2 toxicity (reversible yellowing). All corn plants recovered fully with no yield impact. Downwash turbulence at 1.5m height increased drift risk—recorded wind speeds exceeded 3 m/s during 15% of operations. Agricultural UAV applications maintained a buffer zone around non-target crops as a precautionary measure. For supplementary drift datasets, see nan.
Conclusions
Agricultural UAVs provide effective Spodoptera exigua control in soybean-corn intercropping systems. UAV-A’s cold-atomization system maximizes droplet deposition in lower canopies at 2.5m height and 45 L/ha spray volume. UAV-B performs optimally at 1.5m height with identical spray volume. Both systems enable 30% pesticide reduction without compromising 7-day efficacy (>98%). These findings establish operational benchmarks for agricultural drone deployments in complex cropping systems, highlighting their role in precision pest management. Future work should quantify droplet drift under varying atmospheric conditions to refine environmental safety protocols.