Utilizing Pruning and Leaf Removal to Ripen Grapes and Encourage Cold Tolerance in North Dakota

Experiments were conducted at three North Dakota vineyards located near Buffalo, Clifford, and Wahpeton, ND, in 2011 and repeated at the same locations in 2012 to evaluate the effects of pruning and leaf removal on yield and quality of wine grapes in North Dakota. The application of three pruning treatments limited the vine to a specific number of productive primary buds while the three leaf removal treatments exposed ripening grape clusters to increased sunlight. Variables included length of growth prior to dormant pruning, weight of growth prior to dormant pruning, rate of ripening, total weight of harvested grapes, average weight per grape cluster, average berry weight, average number of clusters per vine, soluble solids concentration, titratable acidity, and pH. Data were analyzed as a CRD with a factorial arrangement. Data were combined across environments where appropriate. Factorial analysis showed varied significance with pruning and shade leaf removal treatments interacting with specific cultivar traits to influence vine growth, grape yield, and grape quality. Pruning and shade leaf removal treatments both had significant impacts on growth with pruning treatments significantly influencing average growth of the longest one-year-old cane and shade leaf removal significantly influencing weight of dormant cane pruning. While impact on yield was minimal, treatment impacts on grape quality showed potential for use of shade leaf removal as means of decreasing titratable acidity levels in harvested grapes. This research supports the use of pruning and shade leaf removal treatments when to influence grape vine growth, vine balance, and fruit ripening. However, proper timing and level of pruning as well as proper timing of shade leaf removal is essential to minimize injury and maximize potential results.