Some effects of girdling, gibberellic acid sprays, bunch thinning and trimming on the sultana

Abstract

Girdling, thinning and trimming bunches and gibberellic acid (GA) treatments were imposed on sultana vines over three years to study their effects on berry size, yield, skin strength, pedicel features and bunch characteristics. A double cut stem girdle (4.8 mm) combined with three GA sprays of 60 p.p.m. (applied at bloom, shatter and two weeks after shatter) and bunch thinning and trimming produced large berries weighing up to 5 g each. However this treatmen1 delayed fruit maturity and produced more compact bunches. Similar sized berries with no delay in maturity and looser bunches were obtained by using the same combination of treatments but reducing the GA sprays to two, one at 10 p.p.m. applied at 50 per cent bloom and the second at 60 p.p.m, at 3-4 mm berry diameter, which was two weeks after shatter. A double cut was more effective than a single cut girdle. Bunch thinning and trimming were necessary for best results but there were no differences in results between trimming to four or six laterals per bunch. Thinning to 15 bunches per vine produced more compact bunches and lower yield than 20 bunches per vine. Berry skin resistance to puncture was increased more effectively by bunch trimming and thinning than by girdling or applying GA. Pedicel length and thickness were increased substantially by applying GA.