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58 WINES&VINES June 2017 GRAPEGROWING PRACTICAL WINERY & VINEYARD HoytShepston_Monthly09 10/31/08 4:44 PM capacity and from that the number of nodes to retain. For example, Markus Keller suggested that to balance-prune Concord vines, growers should retain 55 nodes for the first 500 grams of pruning weight and add 22 nodes for each subsequent 1 kg of pruning weight. 13 Like the Ravaz Index, the nodes retained to pruning weight ratio will de- pend on the grape variety and likely will vary with site and management. An alternate approach we have promoted in New Zealand for Sauvignon Blanc is to count the effective shoot number (ESN). This in- volves counting and grading during dormancy all shoots on a vine using the following grading system: vigorous shoots (larger than 15 mm diameter) = 2; average shoots (10 to 15 mm) = 1; small shoots (7 to 10 mm) = 0.5; and shoots less than 7 mm are ignored. The total plus 5 (to account for any damaged buds that may be in the canopy) gives the number of nodes to retain. The appropriate diameter classes may vary with variety and vineyard site and needs to be evaluated at each vineyard. Counting shoots also allows an estimate of historic vine performance. If the bud burst (ESN / count nodes retained after pruning) is less than 0.90, this suggests blind budding; a value greater than 1.10 implies a significant number of non-count shoots, while 0.9 to 1.1 suggests that an appropriate number of buds were re- tained in the previous growing season. Final thoughts When pruning vines to achieve balance, do not be greedy. Only retain as many nodes to enable vines to ripen the crop adequately. Using a method to quantify vine performance (Ravaz Index, ESN, etc.) will provide a historic record of the vineyard, enabling the viticulturist to assess the inter-sea- sonal and long-term changes in vigor and produc- tivity. Counting shoots and grading shoots using the ESN system provides a simple way of estimat- ing vine potential, but this system needs to be assessed on each property and for each variety. The leaf area: fruit weight ratio largely de- termines the timing and rate of soluble solids accumulation, and it is likely that the optimum ratio will depend on capacity of the site, variety, wine style, vine-training system and canopy management. There is no universal value. When managing vines, the crop load needs to be adjusted to enable sufficient reserves to be accumulated in the roots and trunks to en- able vines to produce good, uniform spring growth. Good viticulture includes managing to an appropriate yield, maintaining good pest and disease control and optimizing nutrition and irrigation. Keeping good records of vine performance will help achieve this. Mike Trought is a principal scientist with Plant and Food Research at the Marlborough Research Centre in Blen- heim, New Zealand. He is an adjunct associate profes- sor at Lincoln University and a fellow of New Zealand Winegrowers. His research includes management of carbohydrate physiology of vines, flowering, fruit set and yield prediction and understanding the influence of soils and environment on fruit composition. SAUVIGNON BLANC'S RESPONSE TO PRUNING TREATMENTS Vines were converted from four canes (48 nodes) and pruned for four years to between 24 and 72 nodes. 8 Yields are expressed as a percentage of the 24-node pruned vines and data is forced through the zero-node origin. Yield (% 24-node pruned vines) 300 250 200 150 100 50 0 0 20 40 60 80 Nodes number retained post-pruning The references for this article are available online at winesandvines.com n 2007 n 2008 n 2009 n 2010