Manage of crop load to improve fruit quality in plums

Abstract The crop load of European plums must be adjusted to achieve high quality with adequate size and skin color in order to attend market requirements. The present study had the objective to investigate the effects of chemical and mechanical thinning, applied isolated and in combination of both, at different phenological stages of Katinka plum growing in Southern Germany. The following thinners were tested: mechanical thinning, chemical thinning with Ammoniumthiosulfate - ATS, Ethephon, Prohexadione-Calcium and Gibberellin. Mechanical thinning treatment isolated or associated with ATS. Significantly increased fruit drop and reduced the yield. It also, increased fruit size and fruit weight when compared to the control plants. Also Ethephon increased fruit drop and fruit size when compared to the control plants. Among to other chemical treatments, no positive effects were observed for fruit thinning when compared to the control plants.