In recent years, the fall armyworm (Spodoptera frugiperda) has emerged as a significant threat to global agriculture, particularly affecting maize crops due to its polyphagous and voracious feeding habits. This pest has rapidly spread across various regions, leading to substantial yield losses and necessitating effective control strategies. Traditional methods of pesticide application, such as manual sprayers, often face challenges in tall crops like maize, especially during later growth stages. The advent of advanced agricultural technologies, including crop spraying drones, offers a promising alternative by enabling efficient and uniform pesticide distribution. In this study, I aimed to evaluate the field efficacy of crop spraying drones compared to conventional electric sprayers in applying two recommended insecticides, chlorantraniliprole and indoxacarb, against fall armyworm in maize. The primary focus was on assessing control effectiveness, persistence, and leaf protection rates, with an emphasis on the practical implications for large-scale integrated pest management using spraying UAVs.
The experiment was conducted in a maize field with the variety “Xianyu 335” planted in early June. The soil type was classified as lou soil, with an organic matter content of 15.97 g/kg and a pH of 7.9. The field maintained good fertility and irrigation conditions, targeting a yield of 600 kg per 667 m². To ensure representative sampling, the trial was designed with five treatments, each replicated three times in a randomized block design. The treatments included applications of 20% chlorantraniliprole suspension concentrate at 10 mL/667 m² and 30% indoxacarb suspension concentrate at 12 mL/667 m², using both a crop spraying drone and an electric sprayer, along with an untreated control. The pesticides were applied on July 10, 2023, during the small trumpet stage of maize growth, coinciding with the peak occurrence of fall armyworm larvae.
The crop spraying drone used was a multi-rotor WSZ-0805 model, operated with a water volume of 45 kg/ha. The drone was flown at a height not exceeding 1.2 m above the maize canopy and a speed of 6 m/s to ensure optimal droplet deposition. In contrast, the electric sprayer (3WD-18J model) was employed with a water volume of 675 kg/ha, applying the pesticides uniformly across the plots. This comparison allowed for a direct evaluation of the efficiency and effectiveness of spraying UAVs versus traditional methods. Data collection involved random sampling of 50 plants per plot, with fixed points monitored for live fall armyworm larvae counts and leaf damage assessments before application and at 2, 7, and 10 days after treatment. The key metrics calculated included insect population reduction rate, control efficacy, and leaf protection rate, using standardized formulas to ensure accuracy and reliability.
The insect population reduction rate was determined using the formula: $$ \text{Reduction rate} = \frac{\text{Pre-spray count} – \text{Post-spray count}}{\text{Pre-spray count}} \times 100\% $$ Control efficacy was calculated as: $$ \text{Control efficacy} = \frac{\text{Treatment reduction rate} – \text{Control reduction rate}}{100 – \text{Control reduction rate}} \times 100\% $$ For leaf protection, the rate was derived from: $$ \text{Leaf protection rate} = \frac{\text{Intact leaves post-spray} – \text{Intact leaves pre-spray}}{\text{Total leaves} – \text{Intact leaves pre-spray}} \times 100\% $$ and the corrected leaf protection rate was: $$ \text{Corrected leaf protection} = \frac{\text{Treatment protection rate} – \text{Control protection rate}}{100 – \text{Control protection rate}} \times 100\% $$ These formulas provided a quantitative basis for comparing the performance of the crop spraying drone and electric sprayer across different insecticides.
The results revealed significant insights into the efficacy of the two insecticides and application methods. Both chlorantraniliprole and indoxacarb demonstrated effective control of fall armyworm, but with distinct characteristics in terms of speed and persistence. The crop spraying drone and electric sprayer showed no statistically significant differences in control efficacy across all assessment periods, highlighting the potential of spraying UAVs as a viable alternative for pesticide application in maize fields. Detailed data on insect population dynamics and control efficacy are summarized in the following table, which illustrates the trends over time.
| Treatment | Initial insect count | Reduction rate at 2 days (%) | Control efficacy at 2 days (%) | Reduction rate at 7 days (%) | Control efficacy at 7 days (%) | Reduction rate at 10 days (%) | Control efficacy at 10 days (%) |
|---|---|---|---|---|---|---|---|
| 20% chlorantraniliprole SC (10 mL/667 m²) with crop spraying drone | 44 | 80.60 | 79.75 | 85.82 | 87.40 | 86.57 | 87.21 |
| 20% chlorantraniliprole SC (10 mL/667 m²) with electric sprayer | 50 | 82.12 | 81.34 | 88.74 | 89.99 | 88.08 | 88.65 |
| 30% indoxacarb SC (12 mL/667 m²) with crop spraying drone | 42 | 85.16 | 84.51 | 71.88 | 75.00 | 67.19 | 68.75 |
| 30% indoxacarb SC (12 mL/667 m²) with electric sprayer | 43 | 86.15 | 85.51 | 73.08 | 76.70 | 68.46 | 69.96 |
| Untreated control | 40 | 4.17 | – | -12.50 | – | -5.00 | – |
As shown in the table, chlorantraniliprole exhibited superior persistence, with control efficacy peaking at 7 days after application for both the crop spraying drone (87.40%) and electric sprayer (89.99%). In contrast, indoxacarb showed higher initial efficacy at 2 days, with values of 84.51% for the spraying UAV and 85.51% for the electric sprayer, but declined significantly by 7 and 10 days. This trend underscores the fast-acting nature of indoxacarb compared to the prolonged effectiveness of chlorantraniliprole. The leaf protection data further corroborated these findings, as illustrated in the subsequent analysis and formulas.
Leaf protection rates were calculated to assess the preventive benefits of the treatments. For chlorantraniliprole applied via crop spraying drone, the leaf protection rate was 85.6% at 7 days and 72.4% at 10 days, while the electric sprayer achieved 87.1% and 74.6%, respectively. This indicates that chlorantraniliprole maintained strong leaf protection over time, aligning with its persistent control efficacy. The relationship between control efficacy and leaf protection can be modeled using a linear approximation: $$ \text{Leaf protection} = k \times \text{Control efficacy} + c $$ where $k$ and $c$ are constants derived from the data. For indoxacarb, the leaf protection rates dropped markedly from 75.2% at 7 days to 26.8% at 10 days for the spraying UAV, and from 76.8% to 28.3% for the electric sprayer, reflecting its reduced longevity. The following table summarizes the leaf protection outcomes, emphasizing the advantages of using a crop spraying drone for consistent coverage.
| Treatment | Leaf protection rate at 7 days (%) | Corrected leaf protection at 7 days (%) | Leaf protection rate at 10 days (%) | Corrected leaf protection at 10 days (%) |
|---|---|---|---|---|
| 20% chlorantraniliprole SC with crop spraying drone | 85.6 | 85.1 | 72.4 | 72.4 |
| 20% chlorantraniliprole SC with electric sprayer | 87.1 | 87.1 | 74.6 | 74.6 |
| 30% indoxacarb SC with crop spraying drone | 75.2 | 75.2 | 26.8 | 26.8 |
| 30% indoxacarb SC with electric sprayer | 76.8 | 76.8 | 28.3 | 28.3 |
| Untreated control | – | – | – | – |
The larval stage distribution of fall armyworm provided additional insights into the mode of action of the insecticides. In plots treated with chlorantraniliprole via crop spraying drone, no early-instar larvae were observed after 7 days, indicating effective residual activity that prevents population resurgence. Conversely, indoxacarb treatments showed the presence of young larvae at later stages, confirming its rapid knockdown but limited persistence. This dynamic can be expressed using a population growth model: $$ N_t = N_0 e^{-rt} $$ where $N_t$ is the population at time $t$, $N_0$ is the initial population, and $r$ is the mortality rate induced by the insecticide. For chlorantraniliprole, $r$ remained high over time, whereas for indoxacarb, $r$ decreased significantly after the initial application.
In this study, the use of a crop spraying drone demonstrated several operational advantages, such as reduced water consumption (45 kg/ha compared to 675 kg/ha for the electric sprayer) and the ability to cover large areas efficiently without direct human contact with pesticides. The flight parameters, including height and speed, were optimized to minimize drift and maximize droplet deposition on the maize canopy. For instance, the droplet distribution efficiency of the spraying UAV can be described by the formula: $$ \text{Deposition efficiency} = \frac{\text{Droplets on target}}{\text{Total droplets released}} \times 100\% $$ which typically exceeds 90% for well-calibrated crop spraying drones under ideal conditions. This high efficiency contributes to the comparable performance between the crop spraying drone and electric sprayer, as observed in the control efficacy results.
Field observations also highlighted the importance of environmental factors in spraying UAV operations. For example, applications during early morning or late afternoon avoided high temperatures that could accelerate evaporation and reduce pesticide efficacy. The integration of real-time data and GPS technology in modern spraying UAVs allows for precise application, reducing the risk of over- or under-spraying. As a result, the crop spraying drone not only matches the effectiveness of traditional methods but also offers scalability for large-scale pest management programs. The economic implications can be modeled using a cost-benefit analysis: $$ \text{Net benefit} = \text{Yield saved} – \text{Cost of application} $$ where the cost includes pesticide, labor, and equipment expenses. Given the efficiency of spraying UAVs, the net benefit is often higher due to lower operational costs and improved coverage.
In conclusion, this evaluation confirms that both chlorantraniliprole and indoxacarb are effective against fall armyworm in maize, with chlorantraniliprole offering prolonged control and indoxacarb providing rapid action. The crop spraying drone proved to be a reliable tool for pesticide application, showing no significant difference in efficacy compared to electric sprayers. This supports the adoption of spraying UAVs in integrated pest management strategies, particularly for tall crops like maize where traditional methods are challenging. Future efforts should focus on optimizing drone parameters, such as nozzle types and flight patterns, to enhance performance under varying field conditions. Additionally, training for operators is crucial to ensure uniform application and maximize the benefits of this technology. Overall, the crop spraying drone represents a transformative approach in agriculture, enabling sustainable and efficient pest control while minimizing environmental impact.
For visual reference, a field image from the trial is available here: nan, showing the application process and crop conditions. This underscores the practical implementation of spraying UAVs in real-world scenarios, further validating their role in modern agriculture.