Delaying Budbreak to Reduce Freeze Damage: Seasonal Vine Performance and Wine Composition in Two Vitis vinifera Cultivars

Spring freeze events pose a threat to vineyard productivity worldwide. We compared two methods to delay grapevine budbreak for freeze avoidance and evaluated their effects on phenology, yield components, fruit composition, and postharvest parameters, including wine chemistry, carbohydrate storage, and bud freeze tolerance. The two methods to delay budbreak were a vegetable oil-based adjuvant (Amigo) applied to dormant buds at 8% and 10% (v/v) and late pruning applied when apical buds reached approximately Eichhorn-Lorenz stage 7. Treatments were applied in 2018 and 2019 on two Vitis vinifera cultivars, Lemberger and Riesling, and compared to a control treatment with no delayed budbreak strategy. Amigo and late pruning delayed budbreak compared to control vines in both years and cultivars. The delay in budbreak varied from three to six days for Amigo 8%, five to eight days for Amigo 10%, and 10 to 11 days later for late pruning. In 2019, there was a freezing event near budbreak. Compared to control vines, late-pruned Lemberger vines had less shoot damage when measured during the growing season and greater yield at harvest. Delayed budbreak treatments did not influence wine chemistry either year or consistently affect carbohydrate storage or bud freeze tolerance in the following dormant season. However, in Riesling, late pruning reduced cluster and berry weight by up to 34 and 22%, respectively, compared to control vines. Furthermore, Amigo 10% may decrease bud survival when applied to Riesling vines. In general, late pruning delayed budbreak more effectively and mitigated freeze damage better than Amigo application without negatively affecting vine health or wine composition; however, the cultivar-dependent effect of late pruning on cluster weight is a consideration prior to adoption.