Early Leaf Removal as a Strategy to Improve Ripening and Lower Cluster Rot in Cool Climate (Vitis vinifera L.) Pinot Grigio

Removal of basal leaves early in the vegetative and reproductive development of grapevines is a tool used to decrease fruit set, lower cluster rot severity, and improving fruit quality. However, the considerable time required for implementation limits utilization by grape growers. Efficient mechanization can potentially mitigate these issues, albeit this practice has not yet been compared to manual application at pre-bloom and after-bloom stages in a cool and humid growing region where cluster rot is the major limitation for yield and fruit quality. The goal of this study was to compare mechanical leaf removal (ME) with the manual (MA) removal of six leaves at the pre-bloom (PB) and after-bloom (AB) phenological stages over two seasons in Pinot Grigio (a tight-clustered cultivar). Fruit-set was only decreased in 2017 by PB-MA, however, PB reduced cluster compactness in each season. The loss of fruit to gray mold was lowered by all leaf removal treatments in drier 2017 season, but only MA treatments mitigated loss from sour rot in that year. This indicates that a clear fruit zone and reduced cluster compactness are both needed to lower the impact of cluster rot disease. Only pre-bloom treatments enhanced fruit quality, likely driven by a similar reduction in cluster compactness. The results suggest that PB-ME may be utilized to decrease fruit loss to gray mold in dry seasons and enhance fruit °Brix. Nevertheless, PB-MA can be an effective means to reduce fruit loss to sour rot in drier seasons and enhance ripening in years with high precipitation during veraison. This information provides a single approach to alleviate two prominent issues facing seasonal management strategies in cool climate viticulture.