Effects of early shading and defoliation on bunch compactness, yield components, and berry composition of aglianico grapevines under warm climate conditions

Prebloom leaf removal is a canopy management practice used in viticulture to decrease bunch compactness at harvest. However, this practice may not be suitable in dry and warm areas because it may expose bunches to excessive direct sunlight, undesirably decreasing titratable acidity and increasing the pH of berry juice. This study was designed to test the hypothesis that shading between preanthesis and fruit set may be used for Aglianico grapevines as an alternative strategy to decrease bunch compactness without removing leaves around the bunches. This treatment was also thought to maintain berry juice acidity at harvest. The following nine treatments were compared: two defoliations (50 and 90% leaf removal), five whole-canopy shadings (10, 30, 50, 75, and 90% reduction of ambient light), one partial canopy shading (using a 30% shade net), and an unshaded and undefoliated control treatment. Fruit set, berry number per bunch, bunch weight, and yield per vine were significantly affected by several of these treatments. Bunch compactness was reduced only by shading in the range of 50 to 90%. Surprisingly, defoliation decreased fruit set but not bunch compactness because the defoliation caused shortening of the total length of the bunch axes. Berry composition was not negatively affected by 50 to 90% shading, whereas defoliations and 10 to 30% shading decreased titratable acidity and increased the pH of the berry juice at harvest. Flower number per bunch in 2010 decreased linearly with decreasing net photosynthesis per shoot measured in 2009 between prebloom and fruit set. The results of this study suggest that early shading may be an efficient alternative practice to decrease bunch compactness without any negative effect on berry juice composition at harvest.