In order to improve the spraying efficiency of cotton chemical topping agents, a field experiment was conducted to compare the effects of 250 g·L−1 mepiquat chloride aqueous solutions sprayed by a T30 unmanned aerial vehicle (UAV) and a boom sprayer. The cotton agronomic parameters, pesticide utilization rate, yield, and fiber quality were determined. The results showed that the pesticide utilization rates of the T30 UAV and the boom sprayer were 48.71% and 30.37%, respectively. After 10, 20, 30, and 40 days of T30 UAV spraying, the plant height inhibition rates of the two varieties of cotton were 12.97%, 13.78%, 20.91%, and 26.14% for Xinluzao 52 and 8.64%, 13.37%, 14.72%, and 18.03% for Huiyuan 720. After spraying with a boom sprayer, the plant height inhibition rates were 7.94%, 11.13%, 18.23%, and 23.69% for Xinluzao 52 and 6.09%, 9.98%, 11.78%, and 15.14% for Huiyuan 720 after 10, 20, 30, and 40 days of spraying. The T30 UAV spraying chemical topping agent was shown to have a significant beneficial effect on the utilization rate of the pesticides, as well as the agronomic properties, yield, and the fiber quality of the cotton.

Defoliant spraying is an important aspect of the mechanized processing of pepper harvesting. Complete and uniform spraying of defoliant could improve the quality of defoliation and reduce the impurity content in processing pepper. In this study, we assessed the effect of aerial spraying of adjuvants on physicochemical properties of defoliant solution and droplet deposition when using an unmanned aerial vehicle (UAV) for defoliation spraying. The results showed that Puliwang was a better aerial spray adjuvant suitable for spraying defoliants for processing pepper using UAVs, with a higher defoliation rate and better droplet deposition. Although the YS-20 adjuvant had a higher droplet deposition amount (0.72 μg/cm2) in the middle layer, its performance was poor in droplet size, density, and coverage. The size and density of the droplets added with the Manniu were basically the same as the Puliwang, even the distribution uniformity was better (the CV of the upper canopy layer was only 33.6%), but the coverage rate was poor. In the treatment with AS-901N, there was no marked increase in droplet size, so evaporation and drift were not improved, eventually resulting in a lower defoliation rate. Puliwang had the highest comprehensive score, followed by AS-910N, YS-20, and Manniu.

The deposition and spreading of pesticide droplets on the surface of plants is a severe challenge to precise pesticide application, which directly affects the pesticide utilization rate and efficacy. Cotton harvest aids are widely used in machine-picked cotton but the effect of formulation and concentration on the droplet behavior and defoliation effect of cotton defoliants is not clear. To clarify the influence of formulation and concentration on the droplet behavior of cotton defoliants, four formulations (suspension concentrate (SC), water dispersible granule (WG), oil dispersion (OD), and wettable powder (WP)) of cotton defoliants were used to prepare different concentrations of harvest aid solutions, according to the spraying volume. The physicochemical properties, droplet impact, and spreading and deposition behavior were studied. The results indicated that the four kinds of harvest aids have good physicochemical properties and can be wet and spread on cotton leaves. The surface tension of the high-concentration harvest aid solution (the spraying volume was less than 1.2 L/667 m2) was increased, which increased the contact angle and reduced the adhesion tension, adhesion work, and the spreading area. Once the harvest aid solution systems impacted the cotton leaves, it could spread to the maximum in a short time (10 ms). The field experiment showed that the droplet spectrum of harvest aids changed slightly, the coefficient of variation (CV) did not exceed 50%, and the defoliation rate was better when the spraying volume was 1.5 L/667 m2. The correlation and principal component analysis showed that the spraying volume (concentration) and coverage were negatively correlated with the defoliation rate, while the viscosity, diffusion factor, and spreading rate were positively correlated with the defoliation rate. Overall, the use of appropriate spraying volume application in cotton fields can improve the performance of spray, increase the effective deposition and wetting spread of defoliants on cotton leaves, further reduce the dosage of defoliants, and improve pesticide utilization. These results can provide a theoretical basis for the scientific preparation and spraying of cotton harvest aid solutions.

A conventional spraying mode and a fully autonomous fruit tree operation mode using a model DJ T30 unmanned aerial vehicle (UAV) were used to control aphids control on elm trees and to clarify the distribution of droplets in elm trees sprayed by a UAV. The effects of six aviation spray adjuvants on elm canopy droplet deposition and aphid control were evaluated. ImageJ software was used to analyze and measure the droplet density and deposition of water sensitive paper in two modes; this was done to calculate the droplet uniformity, depositional penetration, and droplet penetration, and to verify the aphid control effect. The results showed that the droplet density increased by 79.7%-100.7% in the upper canopy and 0-394.1% in the lower canopy without adjuvants in the fully autonomous fruit tree operation mode. The upper canopy deposits increased by 65.7%-179.3%, and the lower canopy increased by 0-152.8%. When adjuvants were added, the droplet density in the upper canopy increased by 49.7-56.1% using Jiexiaofeng (JXF), and the lower canopy increased by 138.2%-177.8% using JXF, 45.8%-141.3% using Beidatong (BDT), 45.5%-92.9% using Gongbei (GB), 0-93.5% using Maisi (MS), and 0-95.2% using Manniu (MN). The deposits of the upper canopy increased by 888.1-1 154.2% using JXF, 0-1 298.3% using MN, 0-343.9% using BDT, 0-422.5% using GB, 0-580.3% using MS. The lower canopy increased by 746.4%-1 426.0% using JXF, 226.2%-231.0% using BDT, 435.8%-644.0% using GB, 255.0%-322.4% using MS, and 249.3%-360.0% using MN. When JXF was added, the droplet uniformity, droplet penetration and depositional penetration were better than when using other adjuvants. The effects of JXF, BDT and GB in controlling aphids was significantly better than other adjuvants (p<0.05). The following control effects were observed; 94.1% with JXF, 93.1% with BDT, and 93.3% with GB after 3 d of application, and 97.9% with JXF, 95.6% with BDT, and 97.1% with GB after 7 d of application. At the same time, the application of the fully autonomous fruit tree operation mode and JXF can effectively improve the density and deposits, which will produce a superposition optimization effect. Our study focuses on the prevention and control of elm aphid infestations based on the operation mode of a UAV and aviation spray adjuvants, which can provide a baseline for the control of diseases and insect pests using UAVs in agriculture and forestry.