THE USE OF COMPETITION FOR CARBOHYDRATES AMONG VEGETATIVE AND REPRODUCTIVE SINKS TO REDUCE FRUIT-SET AND BOTRYTIS BUNCH ROT IN SEYVAL BLANCGRAPEVINES

Three pruning severities and two times of cluster thinning were applie d to Seyval blanc grapevines to vary the quantity of vegetative and re productive sinks at fruit set. Vines were balanced pruned to either 10 , 30, or 60 nodes per 454 g of cane prunings. Half were flower cluster thinned and half post-fruit-set thinned to 15 clusters per 454 g of c ane prunings. Increased sink competition created by a greater number o f apical meristems influenced canopy morphology and reduced cane matur ation, but had no effect on Botrytis bunch rot. Delaying cluster thinn ing until post-fruit-set decreased fruit set, yield, and Botrytis bunc h rot while increasing berry weight and degrees Brix. Decreasing clust er thinning severity eliminated losses in yield from reduced fruit set . Post-set cluster thinning to increase reproductive sink competition and reduce fruit set appears to be a viable cultural practice to reduc e Botrytis bunch rot and improve yields.