Influence of mechanical postveraison leaf removal apical to the cluster zone on delay of fruit ripening in Sangiovese (Vitis vinifera L.) grapevines

Background and Aims: Postveraison limitation of canopy photosynthesis delays grape berry ripening and reduces sugar accumulation, thus lowering the alcohol content of the subsequent wines. This study was designed to evaluate whether similar results could be obtained by defoliation apical to the bunch zone using a leaf-plucking machine when berry sugar content was approximately 16-17°Brix. Methods and Results: In 2011 and 2012, defoliation treatments were applied postveraison to cv. Sangiovese vines (D) on either side of each row using a mechanical leaf remover, and these D vines were compared to a nondefoliated control (C). The machine removed 35% of the leaves on the vine and created a 50-cm vertical window without leaves above the bunch area, but retained a few leaves at the canopy apex (about 0.50m2/vine). In both years, leaf removal reduced the rate of berry sugar accumulation and led to a 1.2 lower harvest °Brix and consequently, a lower wine alcohol (-0.6%) content in D relative to that of C vines. In 2012, sugar content of D vines, monitored in a group of vines that was not harvested, had recovered to that of C vines 2 weeks after harvest. The concentration of total phenolic compounds in the grapes, the chemical and chromatic characteristics of the wines and the replenishment of soluble sugars, starch and total nitrogen in the canes and roots were similar in the D and C vines. Conclusion: To achieve an effective delay in sugar accumulation in the berries, leaves should be removed at 16-17°Brix, and at least 30-35% of vine leaf area should be removed. Significance of the Study: Mechanical removal of leaves postveraison above the bunch zone of Sangiovese can be an easy and economically viable technique for delaying sugar accumulation in the berries and for limiting the alcohol content of wines with no negative impact on desirable composition of either berries or wines. © 2013 Australian Society of Viticulture and Oenology Inc.