Chemical thinning induced by single and sequential application of BA, NAA and metamitron on ‘Gala’ and ‘Golden Delicious’ apple

Abstract

BA, NAA and metamitron (MM) were tested alone or in combination to induce fruit thinning on ‘Gala’ and ‘Golden Delicious’ apple cultivars. In ‘Gala’ 225 mg L-1 MM, 100 mg L-1 BA and 10 mg L-1 NAA were applied while in ‘Golden Delicious’ higher concentration were used: 300 mg L-1 MM, 150 mg L-1 BA and 15 mg L-1 NAA. All the compounds were applied once 7 days after full bloom or 21 days after full bloom or in repeated applications on both dates, always in combination with MM. The application of MM 7 days after full bloom resulted in a weak efficacy in both cultivars. The application of MM 21 days after full bloom, when temperature conditions during and after the application were more favorable, induced a higher efficacy, that results in reduced number of fruits tree-1, improved fruit size and satisfactory return bloom. Individual BA treatments, regardless of application timing and temperature conditions did not induce satisfactory thinning in both cultivars. NAA efficacy was cultivar dependent: early application improved fruit weight and fruit size distribution in ‘Gala’. In ‘Golden Delicious’, the second application reduced the number of fruits tree-1, increased average fruit weight reducing share of small fruit in the total yield. Sequential application of MM together with BA and NAA was the most reliable option for chemical thinning in both cultivars. MM as the second thinner caused slightly over thinning in ‘Gala’, easier to thin than ‘Golden Delicious’. In ‘Golden Delicious’ only sequential early BA together with late MM application simultaneously reduced fruit number, increased fruit size and provided acceptable return bloom. © 2022 International Society for Horticultural Science. All rights reserved.