Abstract
In organic apple growing in South Tyrol, yield control is commonly achieved by removing buds and flowers with mechanical thinning machines and/or lime sulphur sprays. To allow for thinning also later in the season, trials with shading nets have been carried out over several years. By shading trees with close-meshed nets before June fruit drop, photosynthesis in leaves can be drastically reduced. Notwithstanding the good trial results, the method is not used in the field, because shading trees with nets is labour-intensive and expensive. During the last years we therefore tested different substances as alternatives to shading nets. First promising results were obtained with different oily substances. However, based on our current knowledge, negative side effects such as leaf burn and fruit russeting, can not be excluded. In this experiment, the paraffin oil-based product UFO (Ultra Fine Oil) was applied on different apple cultivars and its thinning efficacy and the side effects were recorded. There have been promising results in thinning, but the differences between the varieties were large. It is therefore clear, that the treatments have to be decided individually for each apple cultivar.