Effects of Mechanical Pruning and Mechanical Shoot Positioning on Yield and Quality of Grapes

There is a major research effort throughout the world to modify grapevines so that viticultural practices can be economically mechanized while maintaining or improving yield and quality. To use machines successfully for shoot positioning, pruning, harvesting, and other grape production operations, trellis systems must be devised and shoots positioned to accommodate precise mechanical movement (6, 21). A properly trained vine should allow efficient mechanical pruning to occur without excessive. damage to the vines or reductions in fruit yield and/or quality. Mention of a trademark or proprietary product does not constitute a guarantee or warranty of the product by the University of Arkansas, and does not imply its approval to the exclusion of other products that may also be suitable. One training system that accomplished these objectives was the Geneva Double Curtain training system (GDC), developed by Shaulis et al. (37) in New York. The GDC trellising system doubles the length of cordon per vine, over the Bilateral Cordon system (BC), and with shoot positioning there is an increase in the number of shoots on vigorous vines that can have their basal nodes adequately exposed to sunlight. Most vigorous vines of large-leafed Vitis labrusca L. cultivars with a drooping-shoot growth habit and annual cane prunings of 1.35 kg or more at 240 cm in-the-row spacing may be expected to give the greatest response to the GDC system (17). The GDC trellising system requires a 3-wire trellis with 2 horizontal cordon-support wires, and a single trunk support wire. The cordon support wires should be 180 cm above the ground and 120 cm apart. The vines are cordon trained and short cane pruned (i.e., 4 to 6 nodes). In contrast to Vitis vinifera L., the fruiting canes of Vitis labrusca cordon-trained vines are selected from nodes of very short vertical arms originating with-in the lower 1800 of the horizontal cordon. The cordon must be in continuous contact with the support wire in order to obtain maximum efficiency from mechanical harvesting and pruning. Bilateral cordon (BC) trained Vitis labrusca vines also can be effectively pruned by machine (2,22,23,24). Research in Arkansas (2,23) that compared the 3 major trellising systems used for Concord grapes has shown the BC system to be as productive and to produce comparable fruit quality to the Umbrella Kniffin system; however, the GDC system was more productive than either of the other 2 systems, with no reduction in fruit quality. The BC and GDC system can be totally mechanized; hence, these systems are recommended for Vitis labrusca cultivars in Arkansas. Bilateral cordon (BC) training with spur pruning is currently a common training system in California vineyards (3). However, the fruiting spurs are selected from the upper 180 of the cordon since Vitis vinifera cultivars grow upright. A common BC trellis used for California wine grapes consists of a 2-wire vertical trellis. A 210 cm stake is driven into the ground to a depth of 50 cm at each vine. A 12-gauge high tensile strength (HTS) cordon wire is located about 105 cm above the vineyard floor. Two or three foliage support wires (13-gauge HTS) are moved upward to support the new growth (30). This system can be successfully mechanically pruned.