FLOWER BUD STAGE AND CHILL HOURS INFLUENCE THE ACTIVITY OF GA3 APPLIED TO RABBITEYE BLUEBERRY

Individual flower clusters of 'Tifblue' rabbiteye blueberry (Vaccinium ashei Reade) were treated iwth 300 ppm GA3 at several flower bud stages to determine the activity of the growth regulator in promoting fruit set. Applications were made one time only at a specified stage of flower development, or once followed by a second application. A single application of GA3 when flower buds had elongated but corollas had not expanded (stage 5) led to the largest increase in fruit set. Two applications of GA3, 10 to 18 days apart, increased fruit set compared with a single application at flower developmental stages other than stage 5. Fruit set promoted by a single spray of GA3 imposed on fully expanded corollas (stage 6) decreased with increasing number of chill hours (350, 520, 760, or 1150). Chemical names used: gibberellic acid (GA3).