Using the following two methods, clusters were flower-thinned at full bloom or 3 days after full bloom in GA-treated Delaware grape vines grown in two types of plastic film hauses and their effects on clusters in size and quality were examined at harvest time. The method used were as follows ; a. removal of basal two blanch axes. b. removal of inflorescence apex leaving main axis in the length of 8 cm when applied at full bloom or 9 cm when applied 3 days after full bloom.
Removal of basal two blanch axes either at full bloom or 3 days after full bloom resulted in desirable clusters of 145-150g, which were 15-18% lighter in weight than and almost similar in shape with those of untreated controls. Eventhough removal of inflorescence apex 3 days after full bloom decreased cluster weight by 20%, it did not have hardly any effect on cluster weight when the treatment applied at full bloom. Further, the treatment tended to increase the number of berries per a unit cluster length and also vary the shape of clusters.