Impacts of Early Leaf Removal and Cluster Thinning on Grüner Veltliner Production, Fruit Composition, and Vine Health

Abstract

A traditional crop load regulation technique, cluster thinning (CT), was compared to a more innovative technique, early leaf removal (ELR) applied either at trace bloom (TBLR) or fruit set (FSLR), on high-yielding and vigorous Vitis vinifera Grüner Veltliner. Treatment effects on key production parameters, Botrytis bunch rot, tolerance to winter temperatures, and production costs were evaluated and compared to an untreated control over two years. Compared to CT, we hypothesized that ELR would improve fruit composition, reduce Botrytis bunch rot, and decrease grower costs. Yield regulation imposed by CT was significantly higher (39.3%) than that of TBLR (12.6%) or FSLR (13.3%), but neither CT nor ELR consistently improved fruit chemistry. Our results suggest that the number of leaves removed (five) at trace bloom or fruit set were insufficient to induce a carbohydrate-limiting response, as ELR vines did not have lower fruit set or bud fruitfulness. Concurrently, TBLR and FSLR vines did not show recovery mechanisms such as greater production of lateral leaves or higher shoot efficiency. Although the overall level of bunch rot severity was lower than 5%, ELR consistently decreased bunch rot intensity (TBLR, FSLR) and severity (FSLR). TBLR also improved bud freezing tolerance during vine acclimation in both years. CT was the most expensive treatment, and the lack of a consistent improvement in fruit chemical composition or tolerance to winter temperatures indicated that Grüner Veltliner can properly ripen more than one cluster per shoot.