Mechanical crop thinning and early defoliation as novel tools for yield management in VSP grapevines

Abstract

Cost-effective yield management is becoming fundamental in modern viticulture in order to meet the existing yield regulations in many parts of the world and to improve grape quality. The evaluation of mechanically performed early defoliation and crop thinning, aiming at yield management, and their effects on the vegetative growth, yield components, grape and wine composition, against a non-defoliated, not-thinned control, and manual treatments are presented. Manual and mechanical early defoliation and crop thinning were conducted at pre-bloom and veraison, respectively, on 'Tempranillo' (Vitis vinifera L.) VSP grapevines in season 2009. A detailed description of the mechanical settings and adjustments, based on preliminary results from previous seasons, for the correct performance of both techniques is provided. Whilst total leaf area remained unaltered, yield was drastically reduced by both practices (38-40%), hence the leaf-to-fruit ratio also enhanced with respect to control vines. Cluster weight, berry number, as well as cluster compactness and Botrytis incidence were also reduced in yield regulated vines, but berry weight tended to increase in mechanically thinned vines and remained unaffected in the early defoliated plants. Berry soluble solids, anthocyanins and total phenols, as well as wine alcohol, color density and total phenol index were generally higher in mechanically early defoliated vines. Effective yield control and fruit quality improvement in VSP grapevines may be accomplished mechanically.