Improvement of tablegrape vine fruitfulness by prior season gibberellic acid application during flowering

Gibberellic acid (GA3) spray application during flowering is practiced for berry thinning in commercial vineyards but may influence inflorescence primordia development in latent buds, leading to variability in vine fruitfulness and yield in the following season. The effects of timing (10% capfall to >80% capfall) of GA3 application during flowering on following season yield were evaluated for the commercial cultivar ‘Menindee Seedless’ in a subtropical climate of Queensland, Australia over two seasons. Inflorescences were counted 4–5 weeks after budburst to assess vine fruitfulness in the season following GA3 application. Applied at early flowering (30% capfall) GA3 produced significantly more (122%) inflorescences per vine in the following season compared to the unsprayed control. Application at mid (50% capfall) to late (>80% capfall) flowering stages did not affect inflorescence numbers in the following season when compared to the control, except at ≥70% capfall stage in one of the two seasons. Applied at late flowering (>80% capfall) GA3 resulted in greater berry diameter than application at early flowering (10% capfall). Further evaluation of a double application strategy involving GA3 at both an early and a late stage of flowering to influence both current season berry size and next season fruitfulness is recommended