Optimal pruning of apple and effects on tree architecture, productivity, and fruit quality

Pruning of apple trees is a very labor intensive and expensive part of apple production. As a result, the mechanization of pruning could prove to be a major cost saving development for commercial growers. An essential part of developing an autonomous robotic pruner is determining the best way for the trees to be pruned. Our objective was to determine if there is a difference between pruning styles in terms of crop yield, quality, and light distribution. The data will then be used to develop a set of optimized pruning "rules" that could be easily followed by a robotic pruner. We tested three different pruning styles on two cultivars, 'Pink Lady' and 'Golden Delicious', in two commercial orchards in the state of Indiana. The pruning styles were: Commercial, Rules, and Purdue Horticulture Pruning (PHP). The Commercial treatment was pruned by the growers' orchard crews while the Rules and PHP treatments were pruned by the researchers. Light distribution, total yield, mean fruit weight, total soluble solids (TSS), and starch rating were measured and analyzed for the three treatments at the end of the growing season. TSS was shown to be significantly different in one cultivar while no meaningful differences were seen in mean fruit weight and starch content. There were minimal differences in the yield data for both cultivars. Information gained from this study will be used to help refine the pruning rules for the development of a mechanical pruner and also to help educate growers on best pruning practices.