The applications of B-nine and CCC by either shoot spray or cluster dip 26 days before anthesis increased the berry set of 'Kyoho' grapes. In shoot spray treatments, the highest number of seeded berries per cluster was obtained by B-nine application at 2500 ppm.
In cluster dip treatments, B-nine application at 500 ppm was most effective for the set of seeded berries followed by B-nine at 1000 ppm and CCC at 100 ppm.
Sprays with both chemicals depressed the shoot elongation and the leaf development in almost proportional to the concentrations but such the retardation of shoot growth was not detected in all dip treatments. No consistent relationship was not found between the amounts of nitrogen and sugar in florets collected just prior to anthesis and the increased berry set caused by the treatments.
The mechanism of these promotive effects of the growth retardants on berry set was discussed in relation to shoot growth during the set period.