Fruit set and quality of self-fertile sweet cherries as affected by chemical flower thinning

Self-fertile cherry cultivars can produce an excessive crop of small fruits with low sugar content. In order to prevent overcropping and provide high quality fruits, chemical thinning of flowers is required. Ammonium thiosulfate (ATS), surfactants and plant oils are used to thin flowers, mostly in apple and peach. The purpose of this research was to compare the effectiveness of the blossom thinners ATS, surfactant Silwet and rapeseed oil (Ogriol) in reducing fruit set of the self-fertile sweet cherry cultivars Alex and Sunburst and their potential to improve fruit quality. At lower rates (1 and 2%) ATS did not consistently reduce fruit set, while at higher rate (3%) it produced visible phytotoxicity on the leaves. ATS treatments did not increase the average weight and diameter of fruits. 10 and 30 ml/l Ogriol application did not reduce fruit set significantly or improve fruit quality of self-fertile sweet cherries. The surfactant Silwet applied at the rates of 1 or 3 ml/l was found to consistently thin self-fertile sweet cherry cultivars, leading to better fruit quality.