Vol. 72 No: 3

Title:
Preharvest Applications of Gibberellic Acid Delay Senescence of Florida Grapefruit

Authors:
R.E. MCDONALD, P.D. GREANY, P.E. SHAW and T.G. MCCOLLUM

pp: 461-468

Abstract:
Peel senescence of ‘Marsh’ grapefruit (Citrus paradisi Macf.) was reduced by gibberellic acid (GA) treatment at three production sites in Florida as indicated by resistance to puncture and the retention of green colour. Applications of GA at 49 g ha^-1 plus 0.05% Silwet L-77 were equivalent to 25 g ha^-1 plus 0.1% Silwet L-77. GA at 49 g ha^-1 plus 0.05% Silwet L-77 was more effective than the maximum label amount of GA (145 g ha^-1) without surfactant. GA applications just prior to colourbreak in August and September were found to be most effective. GA treatments increased peel oil compared with controls, but did not affect fruit quality. Chlorophyll and carotene concentrations in October and November were higher in GA-treated fruit than fruit harvested in the remainder of the season. In contrast, there was only a small effect of GA on time to degreen fruit. Leaf drop was accelerated by GA treatment, but was not different from controls at the end of season in two of the three sites tested. The data suggest that GA efficacy is not dependent on application method, but on spray volume and GA dose. Grapefruit susceptibility to fruit fly attack is correlated with peel colour, firmness and oil content, and GA enhances these attributes.

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