Chemical Thinning of Apricot Cultivars: Promising Preliminary Results

The aim of this study was to evaluate the phytotoxicity and the thinning efficacy of ammonium thiosulfate (ATS) and of 6-benzyladenine (BA). In 2007 and in 2008, ATS was applied twice at a concentration of 1.3% (w/v) on the cultivars Orangered, Kioto, Robada, Goldrich, Bergeron, Harostar and Bergarouge. Benzyladenine was applied in 2007 at the end of the blossom and 25 days after at a concentration of 0.75% (v/v) on the cultivars Orangered, Bergarouge and on the hybrid FG4353, and one application was performed in 2008 on Harostar and Bergarouge. No phytotoxicity was induced by these applications independently of the cultivar. Benzyladenine and ATS treated trees exhibited an enhanced fruit drop. A reduction of 50% to 20% using BA and of 65% to 20% using ATS was observed in the number of fruits per linear meter relatively to the untreated plants. Fruit size was enhanced using ATS but, surprisingly, not for BA-treated trees. These results are promising in order to regulate crop load of apricot cultivars. The reasonability of chemical thinning in apricot is discussed, with respect to fruit size, cultivar differences, phenological stage and number of applications, as well as to climatic, technical and economic aspects.