The incidence of rotting of grapes in clusters that are too compact can be corrected, or at least attenuated, with applications of gibberellic acid (GA3) in the pre-flowering stage, when they are one to two centimeters long, using a concentration of 15 ppm
The spraying is generally done in the morning, applying two or three passes to the same plant, avoiding more than one spraying per bunch, which can be easily achieved, since the treated bunch grows quite long in a short time.
It is also recommended to carry out a later treatment, applying gibberellic acid in a 10 ppm solution, when there is approximately 40% of flowering, repeating with the same dose when the bunch presents 80 and 90% of flowering.
The effect of gibberellic acid is manifested by causing damage to the ovules, decreasing the number of berries, and stimulating cell division and growth, which allows an elongation of the rachis and pedicels of the bunch.
Sometimes the use of gibberellic acid is not enough to solve the problem in large grape varieties and compact clusters, making it necessary to thin manually, removing the grains from the inside with scissors.
