Advances in precision crop load management of apple

Crop load management is the single most important management strategy affecting annual profitability of apple orchards. It carries huge economic penalties for over- or under-thinning ($10,000-20,000 difference in crop value per ha), yet it is a practice that is difficult to control and predict. In 2013, we introduced the concept of precision crop load management using: 1) precision pruning with a stepwise removal of flower bud to a pre-determined flower bud load; 2) sequential chemical thinning sprays guided by the use of computer models to adjust the dose and timing of chemical application and to assess the effect of the chemical sprays shortly after application to guide re-application; and 3) precision hand thinning to guide human workers to leave an exact number of fruits per tree. Our experiments over the last five years have shown that leaving too many flower buds during pruning results in reduced efficacy of chemical thinning and a large job of hand thinning. We have also found that precision chemical thinning can result in fruit number per tree close to the pre-determined optimum crop load if the trees are pruned to a recommended level of 1.5-2.0 flower buds per final target fruit number. We are currently working on computer vision and robotic tools to streamline the counting of buds, flowers and fruitlets and guide human or robotic workers in reducing crop load to the optimum.