In spray application contexts, plant leaves are bent and twisted upon droplet impact, which has a significant impact on the droplet’s impact behavior and its deposition effect on the leaves. This study examines the impact behavior of droplets on flexible pepper leaves and develops a mathematical model for droplet spreading and rebound, integrating the effects of leaf bending and torsion via energy conservation and cantilever beam theory. The energy required for leaf bending and twisting due to droplet impact was estimated in accordance with Hooke’s law. The droplets attained their maximum spreading diameter 4 ms post-impact on flexible pepper leaves, with droplet retraction occurring significantly faster on flexible leaves than on rigid ones, resulting in a return to steady state in half the duration required by rigid leaves. This study aims to establish a scientific foundation for optimizing pesticide application strategies and selecting parameters for spraying equipment in pepper production.

In order to investigate the influence of factors on the spray deposition of the spray bar sprayer, using the designed mobile spray bar spray device, the spray height, spray bar travelling speed and spray pressure were selected as the test factors, and the deposition amount of seductive red per unit blade area Y1 and the deposition coefficient of variation Y2 were taken as the evaluation indexes for the test, and the 3-factor, 3-level orthogonal rotary spray deposition test was carried out. The Box-Behnken response surface method was used to analyse and obtain the mathematical model of the spray deposition characteristics of spray height H, spray rod travel speed v and spray pressure P. The influence of each factor on the spray deposition characteristics and the optimal working parameters of the spray machine were obtained according to the regression analysis results. The results show that the forward speed, working height and spray pressure have a significant effect on the spray deposition characteristics, and the degree of influence in the order of the factors from the largest to the smallest is the spray pressure, the working height, the forward speed, the spray pressure, the working height and the spray pressure. The mean value of droplet deposition per unit area is negatively correlated with forward speed and nozzle working height, and positively correlated with spray pressure. The coefficient of variation of deposition is negatively correlated with the spray pressure, positively correlated with the forward speed, and decreases and then increases with the increase of the working height, which indicates that in the case of a certain working height, increasing the spray pressure or reducing the forward speed can effectively improve the uniformity of droplet deposition of the sprayer.