The efficacy of 1-aminocyclopropane-1-carboxylic acid (ACC) as a chemical thinner on apples

K.I. Theron, G.F.A. Lötze, D.A. Scholtz, J.S. Reynolds
The purpose of this study was to evaluate a new chemical thinning molecule, 1-aminocyclopropane-1-carboxylic acid (ACC), on ‘Fuji’ and ‘Cripps’ Red’ apples. ACC was evaluated over two seasons at a range of concentrations from 140 to 560 mg L‑1, applied at different phenological stages from petal fall to 15-20 mm fruitlet diameter. The fruit industry needs a chemical thinning agent that can successfully be applied during the later thinning window (15-20 mm fruitlet diameter) on apples. ACC was compared to industry standard applications, 6-benzyladenine (6-BA) and 1-napthaleneacetic acid (NAA), applied as a tank-mix or individually. In all the trials, ACC proved to be a stronger thinner than the industry standard applications. During both seasons, trials on ‘Fuji’ were disappointing as neither ACC nor the industry standard applications caused satisfactory thinning. ACC application in the 2017/2018 season to young ‘Cripps’ Red’ trees was not successful. However, ACC proved to be very promising when applied to a mature ‘Cripps’ Red’ orchard during the 2018/2019 season. ACC applied at the 15-20 mm fruitlet diameter, thinned successfully, and increased fruit size without decreasing yield. We concluded that the rate of ACC should be between 280 and 560 mg L‑1. No negative effects on stem-end russet, fruit maturity and leaf drop were observed. Further research, however, is needed before final recommendations can be made.
Theron, K.I., Lötze, G.F.A., Scholtz, D.A. and Reynolds, J.S. (2022). The efficacy of 1-aminocyclopropane-1-carboxylic acid (ACC) as a chemical thinner on apples. Acta Hortic. 1341, 15-24
DOI: 10.17660/ActaHortic.2022.1341.3
1-aminocyclopropane-1-carboxylic acid (ACC), 6-benzyladenine (6-BA) and 1-napthaleneacetic acid (NAA), thinning, yield, leaf drop, fruit size