Environmentally-friendly regulation of fruit set in apple trees

Control of fruit set and fruit thinning in apple often involves the use of plant bioregulators, colloquially termed hormones, such as NAA and BA. Their use, however, has been widely criticised due to fruit and food safety and health concerns. The objective of this project was to evaluate alternatives to these conventional thinners. Hence, Azolon and Platina were used in 2002 and 2003 on cvs. 'Gala' and 'Braeburn' apple trees in Klein-Altendorf near Bonn in Germany. Azolon 28, a methylurea mixture, did not enhance fruit thinning or russetting when solely used, but proved a mild to good thinner particularly in cv. 'Gala' when combined with an ethylene releasing compound such as Flordimex. The experiments showed that mild thinners like Azolon also avoid the danger of over-thinning. The second alternative, Platina, is an amino acid mixture, which increased fruit set in cv. 'Braeburn' in 2002 and 2003. This indicates a market potential to prevent pre-harvest fruit drop when applied at a later stage. The results are discussed with respect to fruit yields and quality and potential marketing strategies.