Mechanical yield regulation in winegrapes: Comparison of early defoliation and crop thinning

Background and Aims: Winter pruning and manual bunch thinning are the primary methods for crop regulation in viticulture. Recently, innovative mechanical approaches have been proposed as cost-effective for yield management. The aim of this work was to compare the effectiveness of mechanical early defoliation and mechanical crop thinning on yield regulation, and on grape and wine composition. Methods and Results: The impact of mechanical early defoliation and crop thinning, applied at different timings, was investigated in Vitis vinifera L. cv. Tempranillo vertically shoot-positioned-trained grapevines over two seasons. Effects on yield components, leaf area, botrytis incidence, grape and wine composition were determined. Yield per vine was drastically reduced by both techniques (35-40%). Bunch weight, number of berries per bunch, bunch compactness and botrytis were also reduced by most of the treatments. Total leaf area per vine was not affected, however, the total leaf area-to-yield ratio increased in most cases. Berry soluble solids, anthocyanins and total phenols increased in the grapes. Wines were higher in alcohol and more intensely coloured in mechanical early defoliation treatments in comparison with those of mechanical thinning. Conclusions: Mechanical early defoliation and crop thinning may be suitable and efficient for regulating grape yield and improving grape and wine composition. Early defoliation, however, appeared to be more consistent. Significance of the Study: Effective yield control in winegrapes may be accomplished by mechanical techniques implemented between pre-flowering and veraison. The choice of mechanical technique for yield management may influence the grape and wine composition.