Gibberellic acid (GA 3 ) was applied to the seeded wine grape ‘Seibel 5455’ ( Vitis vinijera × Vitis labrusca ) when 75% of the calyptras had been shed. Fruit set and bunch compactness were decreased by GA 3 at 5‐40 ppm. Yield per vine and sugar and acid contents of the treated berries were not affected. The number of bunches infected by Botrytis cinerea Pers. ex Fr. was substantially reduced by 10 ppm GA3 but not by 20 or 40 ppm. If GA 3 was applied at the start of calyptra shedding, bunches were less compacted than those clusters treated at 50‐100% calyptra fall.
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Murray E. Hopping (1976) studied this question.