• The distinctive behaviors of pesticide droplets in the dense and dispersed regions are clarified during spraying. • In the droplet interaction region, spray droplets below150 μm prefer to merge with those above 150 μm. • Droplet coalescence can improve the size distribution of initial droplets and the uniformity of deposited droplets. • A drift map of the critical drift heights for spray droplets with different sizes is proposed. • The evaporation losses of droplets between 100 and 150 μm are more sensitive to atmospheric conditions and the critical drift height is about 0.5 m. Pesticide spraying for crop protection is to obtain adequate coverage on the target surfaces with a minimum of off-target waste. Understanding the spatial behaviors of spray droplets is critical to regulate pesticide deposition. Here, we investigated the droplet interaction behaviors in the dense region and the transport efficiency of pesticide droplets in the dispersed region. The trajectories were tracked with the discrete phase method verified by the wind tunnel experiment. In the dense region near the nozzle, coalescence between droplets smaller than 150 μm and the larger ones can obviously improve the initial droplet size distribution. The reduction in the proportion of easily drifted droplets, contributed by droplet coalescence, can significantly increase droplet deposition onto the target region. When droplets are gradually dispersing, the critical drift height is proposed and clarified by recognizing the falling distance where the mass transport efficiency begins to reduce rapidly. Once the actual spray height exceeds the critical drift height, narrowing the initial relative span of droplets will not facilitate the pesticide transport efficiency, even aggravating the drift loss. The evaporation losses of droplets smaller than 150 μm are more sensitive to the air temperature and relative humidity. The findings of droplet drift behaviors offer insights into pesticide spraying and also provide a strategy for drift regulation. [Display omitted] [ABSTRACT FROM AUTHOR]