Abstract
The use of transpiration inhibitors to increase June fruit drop has become a common practice in organic fruit growing areas in South Tyrol. However, open questions concerning the management of this thinning technique exist, and there is still potential for improvement. On some cultivars, for example 'Gala', the thinning efficacy of transpiration inhibitors can be considered adequate, and no major phytotoxic symptoms on leaves and fruits are observed. On other cultivars, instead, for example 'Braeburn' and 'Kanzi'®, the fruit thinning effect sometimes is too high, and considerable leaf burn may occur. In addition, the thinning action is not always optimal, because its extent varies depending on crown height. The trials conducted in 2014 and 2015 on the cultivars 'Gala', 'Braeburn' and 'Kanzi'® showed that a reduction in the thinning efficacy and in the occurrence of phytotoxic symptoms on leaves can be obtained by omitting lime sulphur treatments during the period, in which paraffin oils are commonly applied for fruit thinning. Furthermore, more effective and uniform thinning throughout the entire crown height can be achieved by directing sprays to specific crown zones, for example to the top crown zone.