A working model of apple thinning

Early chemical thinning of apples in Australia has become more widely used and successful. Fruit size has been greatly improved and there are bonuses of better keeping quality and regular cropping. To attain this objective, thinning must be predictable or recommendations loose credibility and are not used. Loss of credibility is due to underthinning as much as the fear of overthinning. The challenge in Australia is to remove 90% of potential fruit with chemicals from blossom to four weeks later without overthinning. To do this by hand thinning is neither practical nor economic. Predictability in thinning has been achieved by channeling research findings into a predictive model of fruit thinning. The basis for the model is a mathematical matrix of optimum crop loading. We have used data from our experiments over the last 20 years to construct a computer databank. This information consists of data sets, which are complex and multifactorial. They include combinations of prime factors such as cultivar, rootstock, and primary thinners to be used, age of tree, fruit size required and size of trees. Several modifiers such as last years crop are used to fine-tune the outcome. The system is computerized and is a pathway analysis and can deliver best practice for orchardists. It can also quickly identify areas needing further research.