Effect of Shoot and Cluster Thinning on Vine Perfomance and Fruit Quality of 'Blanc Du Bois'

‘Blanc Du Bois’ is a hybrid bunch grape released by the University of Florida in 1987. It has excellent resistance to Pierce’s Disease caused by Xylella fastidiosa and is cultivated in the southeastern United States.  It has good fruit quality for wine production and several wineries have won awards with wines made from this variety. However, there is a lack of information on the optimal horticultural practices to maximize fruit quality in a subtropical climate. Thus, the objective of this project is to optimize vine vigor and fruit quality of ‘Blanc Du Bois’ through shoot thinning (ST) and manipulation of cropload (CP).  Five-year old vines of ‘Blanc Du Bois’ were shoot thinned at the end of March, when shoots were about 10 cm long or between stages 12 to 15 on the modified Eichorn-Lorenz scale. In May when berries were pea-sized (7 mm), cluster thinning was applied, leaving one cluster (CP1), two clusters (CP2) or three clusters (CP3) per shoot. The experiment was established in a randomized complete block, with no shoot thinning (NST) and three clusters per shoot (CP3) serving as a control. During the growing season, shoot length, leaf area and photosynthesis were measured. Vines were harvested in July for fruit quality measurements (total soluble sugars [°Brix], pH, titratable acidity) and vine performance (yield per vine, cluster weight, berry number and weight). No significant differences were found in the interaction between shoot thinning and cluster thinning; however significant differences were found with shoot thinning and cluster thinning alone. Yield per vine increased in vines that were not shoot thinned with the highest cropload (CP3) when compared to CP1. No significant differences were found between CP2 and CP3.  Shoot thinning significantly affected pH, with ST resulting in lower pH. Cluster thinning increased Brix, with CP1 (lowest cropload) resulting in higher Brix, followed by CP2 and CP3; however there was no difference between CP2 and CP3. No significant effects were found on vine measurements. Although there was no effect from the interaction of shoot thinning and cluster thinning, there was an increase in fruit quality when shoot thinning or cropload management was applied.