Post-veraison mechanical leaf removal delays berry ripening on 'Sangiovese' and 'Montepulciano' grapevines

Ripe berries often results too rich in sugar in recent years, though harvest is done in advance, thus the hypothesis of limiting berry sugar accumulation by lowering canopy carbon assimilation during ripening phase was tested in 2011 season. Post-veraison removal of the most functional leaves on the upper part of the canopy of vertical shoot positioned medium-vigour 'Sangiovese' and 'Montepulciano' grapevines was performed mechanically in a hillside vineyard established in 2006 nearby Ancona, Central Italy. Grapevines, 2.75x1.2 m spaced, were cordon trained and spur pruned. The tractor-mounted Plucker leaf stripper (Tanesini Technology, Faenza, Italy) operated on both side of the canopy on August 26, 2011 (i.e. 28 days after veraison and 34 days before harvest), when berry sugar concentration was already at 22°Brix and total acidity was still around 9-10 g/L. The leaf stripper removed from the upper part of the canopy (0.7-1.0 m above the cordon) 60 and 29% of the leaf area in 'Sangiovese' and 'Montepulciano' respectively. As a consequence, total leaf area per vine lowered by 25% in 'Sangiovese' and 14% in 'Montepulciano'. Leaf/fruit ratio at harvest lowered from 1.18 to 0.73 m2/kg in 'Sangiovese' and from 1.23 to 1.03 m2/kg in 'Montepulciano'. The significant reduction of total leaf area registered in post-veraison defoliated grapevines of both cultivars did not affect yield per vine, bunch and berry weight, total acidity and pH of the must, but lowered juice soluble solids concentration (-0.7°Brix in comparison to control in both cultivars). Post-veraison defoliation negatively affected anthocyanins and polyphenols concentration at harvest in 'Montepulciano' grapevines, but not in 'Sangiovese' ones. Thus mechanical leaf removal, quick and easy to perform late in the season to obtain grapes less rich in sugar, may be detrimental to berry colour according to genotype and should be carefully tested on black-berried cultivars before large scale application.