Early defoliation (hand vs mechanical) for improved crop control and grape composition in Sangiovese (Vitis vinifera L.)

Background and Aims: The number of pre-bloom source leaves is a primary determinant of subsequent fruitset. Accordingly, we tested whether pre- and post-bloom hand (HD) and mechanical (MD) defoliation are effective in limiting the yield of a high-cropping cultivar such as Sangiovese in a 3-year field study. Methods and Results: The first six basal leaves and any laterals were removed by hand, and the same area was subjected to MD, the latter removing 48.3% of the leaf area removed manually. Both treatments significantly reduced fruitset, yield per shoot, bunch weight, berries per bunch and bunch compactness. Yield/ha declined from 32.8 tons in control vines to 24.4 and 19.0 tons for MD and HD (pre- and post-bloom treatment means), respectively. Leaf-to-fruit ratios were unaffected by defoliation as source loss was fully offset by yield decline. Soluble solid concentration and total anthocyanins on a fresh-weight basis increased by 2.4°Brix and 0.2 mg/g in HD and by 2.2°Brix and 0.08 mg/g in MD as compared with that in non-defoliated control. Conclusions: Although results from HD reinforce the physiological basis of the technique's effectiveness, MD proved likewise effective in reducing yield and improving grape quality. Significance of the Study: Early MD has the potential to regulate yield in a timely and cost-effective fashion. © 2008 Australian Society of Viticulture and Oenology Inc.