Unmanned aerial vehicles (UAVs) are widely used in field pesticide spray operations due to their wide applicability and high operational efficiency. However, their high spray height and fine pesticide droplets lead to a greater risk of drift and likely different droplet deposition outcomes compared to the expectation. So far, most of the previous studies have used direct field methods on UAVs’ droplet deposition characteristics and there have been few carried out in wind tunnels. Thus, in this paper, a simulated UAV platform equipped with TeeJet 80-015 VP fan nozzles was utilized to study the droplet deposition characteristics in a wind tunnel. The droplet deposition amount and drift potential reduction percentage (DPRP) under different spray parameters were obtained. The results showed that when the rotor was open, the deposition amount in the target area increased by 2.6 times and the drift deposition amount decreased by 7.3 times when spraying tap water at 3 m/s wind speed and 3 bar pressure. Faster wind speeds led to greater drift deposition amounts and a lower DPRP, but higher pressures resulted in greater drift deposition amounts and a larger DPRP. The 30 g/L PEG-20000 solution has a higher droplet size and smaller relative droplet spectrum width R_S, resulting in the deposition amount in the target area increasing by 9.13% on average and the drift amount decreasing by 24.7% on average, and it can be used as an anti-drift additive when needed. The research results can provide reference and technical support for UAV wind tunnel tests and field operation specifications.

Plant protection unmanned aircraft vehicles (UAVs) were developed rapidly in China. The operation performances of different models of UAVs were different. This paper systematically studied droplet deposition distribution; pesticide-mixture utilization rate; operational efficiency; wheat-disease control efficacy; and a comprehensive score of three types of UAVs, a boom sprayer, and a knapsack sprayer. The results showed the descending order of the droplet penetration rate of the pesticide application equipment (PAE) was boom sprayer; UAVs; and knapsack sprayer. The pesticide-mixture utilization rates of the UAVs and boom sprayer were more than 50% while that of the knapsack electric sprayer was only 27.8%. The UAVs’ average labor productivity was 5.75 ha per man-hour, which was slightly less than that of the boom sprayer and 21.3 times that of the knapsack sprayer. The control efficacy of each machine on wheat Fusarium head blight was more than 90%. The average performance comprehensive score of the UAVs was 0.812, which was slightly lower than the score of 0.929 for the 3WPZ-700 self-propelled boom sprayer but much higher than the score of 0.399 for the 3WBD-18 knapsack electric sprayer. The results clearly showed the potential of UAVs for improving the pesticide-mixture utilization rate and operational efficiency, as well as the wheat Fusarium head blight control efficacy.

Pesticide application is an essential means of controlling plant diseases and pests in citrus orchards. In recent years, fixed spraying systems have gradually been used as alternatives to traditional sprayers and manual sprayers in some hilly citrus orchards. In this paper, influences of fixed system spraying parameters, such as droplet size and spraying height, on spraying quality were elucidated and analyzed. The performances of two nozzle types, pressure-swirl nozzles and fixed spray plate sprinklers, were assessed and compared by effective droplet coverage ratio (DCR), droplet distribution uniformity coefficient of variation (CV), and droplet penetration ratio (DPR). The results showed that appropriately increasing droplet size and spraying height could improve the DCR and distribution uniformity of pressure-swirl nozzles. The DCR and distribution uniformity of fixed spray plate sprinklers had a positive correlation with droplet size, while spraying height had no significant effect on these variables. Additionally, with the increase in droplet size, DPR initially increased and then gradually decreased. The optimized results showed that the optimal parameters for pressure-swirl nozzles were a droplet size of 240 μm and spraying height of 100 cm, while for fixed spray plate sprinklers, the results were a droplet size of 240 μm and spraying height of 50 cm. Comparison results showed that the spraying quality of fixed spray plate sprinklers was better overall, with values of DCR, CV, and DPR being 37.15%, 24.20%, and 71.67%, respectively, while the corresponding values for pressure-swirl nozzles were 39.65%, 35.41%, and 56.02%. Based on the above results and the occurrence rule of citrus pests and disease, the optimal spraying parameters of fixed spraying systems were selected to control the Asian citrus psyllid Diaphorina citri. Furthermore, the effect of fixed spraying systems on controlling Diaphorina citri reached the maximum at 3 days after spraying, which was 97.83%, and the effect declined at 14 days after spraying, which was 85.47%. This study provides valuable scientific references for guiding the application of fixed spraying systems in hilly citrus orchards.

Under soybean–corn intercropping in China, quizalofop-p-ethyl is recommended as a herbicide for stem and leaf treatment after soybean seedling. Nonetheless, herbicide drift during spraying may lead to environmental contamination and damage to the corn plants. In order to clearly show the threshold of the drift deposition amount of quizalofop-p-ethyl that causes herbicide damage to corn, we used a bioassay spray tower to spray quizalofop-p-ethyl herbicide on corn in the laboratory and a boom sprayer to spray quizalofop-p-ethyl herbicide, which drifts to corn in the field, to study and evaluate the damage quizalofop-p-ethyl herbicide causes to corn under different spray volumes and drift deposition rates. The results showed that under a drift deposition rate of 1% of three spray volumes, the corn showed no symptoms of herbicide damage and their plant height was not inhibited 14 days after spray; under a spray volume of 150 L/ha and a drift deposition rate of 5%, the corn showed symptoms of mild herbicide damage but their plant height was not inhibited 14 days after spray, while the corn showed symptoms of moderate herbicide damage and their plant height was slightly and moderately inhibited, respectively, under the spray volumes of 300 L/ha and 450 L/ha; under drift deposition rates of 10% and 30% of three spray volumes, half or more of the corn in each treatment withered and their plant height was severely inhibited or completely inhibited. Under the same spray volume, the symptoms of herbicide damage and the inhibition rate of plant height increased with the increase in the drift deposition rate; under the same drift deposition amount, the symptoms of herbicide damage and the inhibition rate of plant height increased with a decrease in the spray volume. The effect of the drift deposition rate on the symptoms of herbicide damage and plant height was extremely significant, but the spray volume was not significant. The drift deposition rates for 10% inhibition and no inhibition of corn plant height were 5.70% (R₁₀) and 5.05% (R₀) under spray volume of 150 L/ha, 4.56% (R₁₀) and 1.23% (R₀) under 300 L/ha, and 3.31% (R₁₀) and 1.86% (R₀) under 450 L/ha, respectively. When the herbicide was sprayed in the field using a soybean–corn-dedicated plant protection machine under the spray volume of 450 L/ha, the drift deposition rate ranged from 1.22% to 1.69%, and the corn did not produce symptoms of herbicide damage and plant height was not inhibited 14 days after the spray. In actual weeding operations, it is better to ensure that the drift deposition rate of quizalofop-p-ethyl is below R₀ by setting reasonable operational parameters, using anti-drift nozzles or additives, and so on, and, at most, not more than R₁₀. This study clarified the drift hazard of quizalofop-p-ethyl herbicide on corn and the safety value of the herbicide drift deposition amount, which provided data support for the standardized use of quizalofop-p-ethyl herbicide under soybean–corn intercropping and guidance for the safe production of field corn.

Adjuvants are frequently incorporated into crop protection operations to modulate the droplet characteristics by diminishing the surface tension (ST) and contact angle (CA), thereby positively influencing the wetting and spreading behavior of the droplets. However, there are no quantitative conclusions on the extent to which the amount of adjuvant added affects droplet properties. Therefore, the decision to add spraying adjuvants in actual pesticide spraying operations relies on the operator’s experience. In this study, we investigated the effect of a surfactant additive (KAO A-200) on the droplet properties and deposition of prochloraz emulsion in water (PEW) solution for crop protection in unmanned aerial vehicle (UAV) aerial spraying. Three KAO A-200 additive concentrations of 0.42%, 0.83% and 1.67% and four solution concentrations of 2.5%, 3.33%, 4.17% and 5% of PEW were set to evaluate the droplet properties of PEW solution with ST and CA as assessment indicators. The results show that the average STs of adjuvant solution droplets tended to decrease as the concentration of KAO A-200 increased. According to the optimal concentration, the KAO A-200 addition concentration of 0.83% was therefore determined to be the most appropriate dosage. With the appropriate KAO A-200 dosage condition, the results show that the average STs increased as PEW solution concentration increased, while the average CAs of PEW solution droplets showed a first decreasing and then increasing trend. The “4.17% concentration PEW (22.5 g a.i./1.2 L) + 0.83% concentration KAO A-200” condition was selected as the optimized combination for crop protection UAV field aerial spraying tests. The test showed that the coverage rate of PEW solution droplets on the upper and lower layers of oilseed rape canopy increased by 71.47% and 41.55%, the deposition density increased by 71.91% and 98.45%, and the coefficient of variation in droplet deposition decreased by 44.41% and 48.13%, respectively. These results are significantly better than those obtained without the adjuvant addition.

Maize–soybean intercropping can increase soybean yields and stabilize maize yields, and this practice has been widely promoted in China. Fluroxypyr is a recommended herbicide for maize seedlings, and its drift will cause phytotoxicity to neighboring soybean seedlings. A laboratory toxicity test was performed on soybeans by using a mobile bioassay spray tower. It showed that both the carrier volume and the drift deposition rate of fluroxypyr significantly influenced soybean fresh weight. The soybean fresh weight inhibition rate increased with the increase in the drift deposition rate, especially in the range of 1% to 6%, and soybean fresh weight decreased rapidly. The lack of fit R² was 0.6875, with a 9% maximum deviation between experimental values and simulated values. The drift deposition rate upper threshold for mild phytotoxicity (10% fresh weight inhibition rate, ED₁₀) was determined to be 3.35%, while the threshold for no phytotoxicity (0% fresh weight inhibition rate, ED₀) was 1.01%. To ensure soybean safety, isolation devices and anti-drift nozzles were installed on the boom sprayer to maintain drift below ED₀ or, at most, ED₁₀. Maize seedling strip weed control field tests showed that the highest drift deposition rate was 0.689% under the carrier volume of 330 L·ha⁻¹. There was no phytotoxicity observed on soybeans after 21 days of application, which was consistent with laboratory research results. In this study, the phytotoxicity risk and safe thresholds for the fluroxypyr drift on soybean seedlings were established, which provide a theoretical basis for the safe production of soybeans.