Crop regulation in organic grown apples - results of different trials on three different sites.

Over a period of five years (2009-2013) different thinning methods and compounds were evaluated at three different sites within the BOLN project “Increasing crop safety and optimizing of crop loading of organic grown pome fruit” (FKZ 06OE197). Just a small extract of all results will be presented here. The trials were carried out in Weinsberg with the cultivars ‘Opal’ and ‘Pinova’, in Klein-Altendorf with the cultivar ‘Gala’ and in Jork with the cultivars ‘Elstar’ and ‘Braeburn’. Except for these cultivars further cultivars were used in other trials, not described here. The strength of thinning was adapted each year to the intensity of flowering. In different trials thinning by hand was compared to thinning with the Darwin rope thinner, lime sulphur, sunflower lecithin, potassium-bicarbonate (Armicarb) and common salt or combinations of it. Using the Darwin rope thinner alone or in combination with lime sulphur showed the best results. Armicarb showed a very good thinning effect, too, but phytotoxicity on the leaves was observed. It led partly to an overthinning and increased russetting. Lime sulphur, sunflower lecithin and -oil worked partly, as well, but not as good as the other treatments and sometimes not, depending on the year and variety.