Spray deposition profiles in pome fruit trees: effects of sprayer design, training system and tree foliage

Air assisted orchard sprayers are characterized by a strong airflow that carries the pesticide droplets to the target canopy and assist in moving the plant parts to allow deposition throughout the whole tree. It has been shown before that different designs of orchard sprayers result in different airflow profiles, but it is still unclear whether these differences strongly affect on-target spray distribution, and what is the role of tree architecture. Here we present an in-field analysis of the on-target deposition profiles from three distinct sprayer types in trees of four different apple and pear training systems. The results obtained showed that there was a strong relationship between the vertical leaf deposition profile and the outlet air flow pattern from the sprayers. Stronger air assistance (higher air speed) was directly correlated to a higher on-target deposition. It was also observed that directing nozzles towards the target is always an advantage irrespective of tree architecture. Tree characteristics such as total leaf cover, leaf wall porosity and tree volume strongly affected the total on-target deposition, further confirming previous claims that ground surface area alone is an incorrect measure for dose calculation in fruit trees.