Identification of a defoliation severity threshold for changing fruitset, bunch morphology and fruit composition in Pinot Noir

Background and Aims: Early defoliation has been proposed as a tool to reduce bunch susceptibility to fungal infections through a reduction in bunch compactness. This research aims to determine the desired level of defoliation producing looser bunches and to investigate the impact of the application of early defoliation on Pinot Noir vines under cool climate conditions. Methods and Results: We applied leaf removal treatments at full flowering or EL-20 phenological stage on Pinot Noir in 2 consecutive years using five levels of defoliation: no leaves removed, and leaves removed from four, six, eight and ten basal nodes. The effects on fruitset, bunch morphology, fruit chemistry, yield and rot severity were recorded. We identified the defoliation of eight basal nodes as the threshold resulting in significantly lower fruitset. The removal of eight or ten leaves reduced bunch compactness but did not alter the proportion of rot. Finally, fruit composition at harvest of the treated vines was found to be improved compared with that of the control vines. Conclusions: The defoliation of six to eight basal nodes at full flowering can regulate fruitset and bunch compactness in Pinot Noir under cool climate conditions. Application over 2 years showed no adverse effects on bud fruitfulness or vine performance the following year. Significance of the Study: Early leaf removal can be an efficient tool to alter bunch architecture, yield and fruit composition without impacting vine health.