Guidelines for the preparation of table grapes in SA for export 2025/2026_ND

FIGURE 2. Grapevine flowers, of which some still have calyptras and others show five stamens. Credit: Gawie van der Merwe.

Gibberellic acid Gibberellic acid is a naturally occurring growth regulator in plants. The gibberellic acid used in grapevines is called GA 3 . Gibberellic acid stimulates cell enlargement. When low doses are applied during full bloom, it promotes the artificial thinning of bunches (page 7). When high doses are applied at a berry diameter of 6–8 mm or later, it causes berry enlargement. The formation of fertile buds on new green shoots of the current season (initiation and differentiation) occurs from flowering and set until approximately 10 weeks after flowering. Complete coverage with gibberellic acid during initiation and the first phases of differentiation can compromise fertility, especially when doses exceed the recommended dose (see cultivar-specific guidelines and product labels). Electrostatic spray pumps can be used to spray for berry enlargement without negatively impacting fertility. Gibberellic acid must be applied under slow-drying conditions. Excessively high doses of gibberellic acid can negatively affect table-grape shelf life. In his research, Prof. Zoffoli of Chile found that the cuticle thins more when more gibberellic acid is applied. The cuticle is a thin, waxy layer on the epidermis. It protects the berry. When gibberellic acid is applied under nets, the dose should be reduced by approximately 30%, because the vines react much better under nets. A regular dose could, therefore, result in berries becoming too large.

10 SATI GUIDELINES FOR THE PREPARATION OF TABLE GRAPES IN SOUTH AFRICA FOR EXPORT