Thinning of ’Golden Delicious’ apples with the combination of ethephon and CPPU

Abstract

A synthetic cytokinin forchlorfenuron (CPPU) 5 ppm was sprayed at the time of petal fall (PF) on eight years old ’Golden Delicious’/M.9 apple trees with the aim of enlarging the fruit growth. Since CPPU is not recognized as a thinning agent which increases the return bloom, a low dose of ethephon was sprayed on CPPU treated trees to enhance flower bud formation and increase flowering in the next season. Ethephon was applied in successive treatments (alone or in the combination with CPPU) 3 x 30 ppm or 5 x 50 ppm, starting at PF, and continued in week intervals. The single application of CPPU 5 ppm or the combination of ethephon 3 x 30 ppm with CPPU 5 ppm decreased the fruit set and enhanced the fruit growth to reach the commercial demand. The combination spraying of ethephon 5 x 50 ppm + CPPU 2 x 5 ppm resulted in a too strong thinning response while the yield of bigger size fruit was not enhanced. Thealone application of ethephon 3 x 30 ppm had no influence on the fruit thinning or fruit weight while the application ofethephon 5 x 50 ppm reduced the fruit set but, consequently, did not enhance the fruit growth. None of the treatments influenced the return bloom.