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56 WINES&VINES June 2017 GRAPEGROWING PRACTICAL WINERY & VINEYARD However, achieving consistency in vine balance in a vineyard is not easy, and several measures have been used to define a balanced vine. These are usually comprised of a ratio between vegetative and repro- ductive growth. Of these, the Ravaz Index, (the fruit yield/dormant pruning weight following harvest) is probably the most widely used. The ratio was developed by Louis Ravaz in the early 1900s, when he concluded that higher crop loads resulted in sick vines. 15 The develop- ment of the Ravaz Index (elegantly recently summarized by Mark Mat- thews) 15 remains widely used when quantifying vine balance. However, the optimum Ravaz Index described in the literature can range from 5 to 10, with the differ- ent ratios reflecting site, variety and production goals. Other indices have been used to quantify vine balance. These indices have been summarized by Peter Dry et al. 5 and include total leaf area (m 2 )/fruit weight (kg) per vine, pruning weight (kg) per unit canopy length (m) and mean cane weight (grams). However, like the Ravaz Index, each of these indices has a range, and one can conclude that there is no universal value, but recording an index provides the viticulturist with useful data about consistency be- tween seasons and a target index measure for a particular site. Experiments undertaken on Sauvignon Blanc in New Zealand investigated the extent to which vines pruned to a fixed node num- ber for several years accommo- dated differences in retained nodes. Vines were pruned to re- tain between 24 and 72 nodes each year for four years. 9 In the first year, yield reflected the num- ber of nodes retained, and vines with 72 nodes produced a yield 76% greater than those pruned to 36 nodes. (See "Sauvignon Blanc's Response to Pruning Treatments" on page 58.) However, after four years, the difference was 29%, as the increased bud number led to reduced bud burst and thinner shoots (and thus canes), fewer clusters per shoot and smaller clusters. Vineyard Tools Battery Powered Pruning Shears • 1.25-inch and 1.5-inch cutting capacity models • 15,000 pruning cuts per battery charge • Includes lithium battery, harness, holster and carrying case www.zenportindustries.com | 503-524-7289 Gra ing Tools w zenportindustri Tying Tools & Supplies Harvest Shears ineyard T ols Pruning | Gra ing | Tying | Harvest Custom made - Handcrafted Barrels THINNING AND TRIMMING ON SOLUBLE SOLIDS AND TITRATABLE ACIDITY Mature Sauvignon Blanc vines were trimmed to retain 12 or six leaves per shoot either unthinned (100% crop) or had all fruit removed from alternate shoots (50% crop) 12 leaves, 50% crop; 12 leaves, 100% crop; six leaves, 50% crop; six leaves 100% crop. 15 Note: Vines with 12 leaves and a full crop accumulate soluble solids at an equivalent rate to those with six leaves and half crop. Soluble solids 26 24 22 20 18 16 14 12 10 8 6 4 0 10 20 30 40 50 60 70 80 90 100 110 Day of the Year Titratable acidity (g/L) 45 40 35 30 25 20 15 10 5 0 n 12L 50% crop n 12L 100% crop n 6L 50% crop n 6L 100% crop