Gibberellic Acid Bloom Sprays Reduce Fruit Set and Improve Packable Yield of ‘Autumn Royal’ Table Grapes

Abstract

A three-year study (1997-1999) examined the effects of gibberellic acid (0, 5, 10, 15 or 20 g•ha ^-1GA ₃) applied at bloom (approximately 80% capfall) on the berry growth, fruit composition and productivity of ‘Autumn Royal’ table grapes ( Vitis viniferaL.). The results indicate that 5 g•ha ^-1GA ₃was the optimum treatment for this cultivar, significantly reducing berry set and cluster compactness, as well as the amount of fruit per vine with bunch rot, compared to the control. This treatment also increased berry length and reduced the number of seed traces per berry, but had no effect on berry weight or diameter. The packable yield of vines treated with 5 g•ha ^-1GA ₃were either similar to or significantly greater than the control, while rates ≥ 10 g•ha ^-1reduced vine productivity and fruit growth, and were therefore unacceptable.