Ammonium thiosulphate and 6-benzyladenine improve the crop load and fruit quality of 'Delicious' apple

Four trials were conducted over 3 years to assess the effect of ammonium thiosulfate (ATS) as a blossom thinner of 'Delicious' apple trees. In addition to determining the optimal concentration of ATS and the effectiveness of multiple applications, the effect on fruit quality was assessed. A program using ATS at bloom and 6-benzyladenine (BA) applied postbloom was examined. Multiple applications of ATS reduced crop load more than a single application. A concentration of 1.0% (v/v, 5800 mg/L) applied twice during the flowering period is recommended, with the first application at 20% bloom and the second at 80% bloom. Fruit firmness and sugar content were increased by ATS, and a positive relationship between fruit weight and sugar content and between fruit weight and firmness was demonstrated. ATS can also be effectively combined in a program with BA with the added benefits of increases in fruit size, firmness and sugar content; however, caution is advised to prevent over-thinning. © CSIRO 2007.