Identifying an Early Leaf Removal Threshold for Grüner Veltliner, a High-Yielding, High-Vigor Cultivar

Background and goals: Early leaf removal (ELR) is a canopy management practice that can reduce bunch rot and improve fruit maturity by modifying cluster architecture and fruit zone microclimate. The goal of this study was to identify an ELR threshold that balances improvements to fruit quality and reductions in yield for a highly vegetative and high-yielding Vitis vinifera cultivar grown in the eastern United States, Grüner Veltliner.

Methods and key findings: Over two consecutive years, we applied a wide range of ELR severities (three to 12 leaves per shoot) at trace bloom (Eichhorn-Lorenz [E-L] stage 19) and evaluated relationships between increasing ELR severity and fruit set, yield param-eters, fruit maturity, bunch rot, and juice volatile composition at harvest. In the first year, increasing ELR gradually reduced fruit set, subsequently lowering yield via reducing berry number and cluster weights. Additionally, ELR increased fruit ripeness while reducing rot incidence. However, extreme ELR (10 to 12 leaves per shoot) negatively affected inflorescence floret number and fruitfulness in the following year. In the second year, only high ELR severities (eight to 12 leaves per shoot) reduced yield parameters, and improvements in fruit ripeness or bunch rot were not observed, likely because of poor weather conditions during fruit ripening. The impact of increasing ELR severities on juice volatile composition was largely limited to benzaldehyde (a volatile phenylpropanoid), which was negatively affected by ELR in both years.

Conclusions and significance: Removal of six to eight leaves per shoot appeared to be the optimal ELR severities for grapegrowers seeking crop management and rot reduction for high-yielding cultivars like Grüner Veltliner. However, as reported in the second year of this study, the effects of ELR may vary by year and be limited by unfavorable weather conditions.