William Nail, The Connecticut Agricultural Experiment Station
The goals of training mature vines are to complement the pruning strategies employed. The principal goal is to expose as much leaf surface area, and usually fruit, to as much sunlight as possible. Well-exposed leaves are photosynthetically active, resulting in increased fruit quality and vine health. Shaded leaves do not contribute significantly to whole-vine photosynthesis, and may even become a carbon drain on the vine. Fruit exposed to sunlight increases berry metabolism during the ripening process through a combination of increased temperature and, especially with red cultivars, direct sunlight effects (Spayd et al., 2002).
The exact practices employed to achieve these goals will depend on the training system being used. The examples used are designed for the two simplest and most common training systems, vertical shoot positioning (VSP) and the high wire Hudson River Umbrella (HRU). The principles can be adapted to other training systems, such as those described in Sunlight Into Wine (Smart and Robinson, 1991). The principles are applicable to both spur-pruned (cordon) and cane-pruned vines in most training systems. Growers can adapt these principles to their own growing situations, depending on practical matters such as local environmental conditions, available labor or mechanization, and desired yield and fruit quality.
Mature vines grow very rapidly early in the growing season. If certain management activities are not completed on time, they can become unmanageable within a week, so attention must be paid to vine phenology. If growth gets out of hand, it can cost the grower more money in management and may lead to over-crowding, disease infection, etc.
These may need to be adapted to your local conditions, and are listed in approximate chronological order:
1. Thin shoots to four to five fruitful shoots per linear foot of row. Selectively remove non-fruitful shoots before fruitful shoots. This is best if done before bloom when inflorescences are visible and the shoot is short (less than 6 inches in length). If the shoots are too long, they can not be removed as easily and may result in problems with shoot removal.
2. Remove all young shoots from the trunk--those growing between the base of the vine and about four to six inches below the fruit zone. This is easily done by rubbing gloved hands up and down the trunk(s). Renewal shoots at the base and in the fruit zone may be reserved, depending on your management practices.
3. Thin fruit post-fruit set if the crop is too large to maintain desired fruit quality or vine balance. Selective removal of distal clusters is usually preferable, as they develop slightly later than basal clusters. In some cases, removal of the distal cluster may be preferred to position fruit so clusters are not touching (avoid disease development).
4. Train shoots up (for VSP) or down (for HRU). Multiple passes are usually necessary to achieve proper season-long shoot positioning. For VSP, shoots are tucked in or tied to trellis catch wires. Depending on the trellis, shoots are either tucked under or tied to permanently placed wires, or catch wires are moved into position in the trellis as the shoots grow. Downward positioned shoots are "combed" into place on both sides of the canopy. In both situations, shoots should be vertical and not allowed to grow horizontally along the vine row.
5. Remove leaves in the fruit zone if desired. This exposes fruit to sunlight, which can be beneficial to fruit quality, especially in cool growing areas. Leaf removal also allows fruit to dry earlier in the day if moisture is a concern, and allows for better spray penetration for disease and insect control. This should be done after fruit set. The later leaf removal is done, the greater the possibility of sun scald damage on fruit, and the effects on fruit ripening and composition diminish.
6. Both vertical and lateral hedging are frequently employed on VSP and related systems to prevent leaf and fruit shading and reduce between-row crowding. Top hedging, especially if done earlier in the season, tends to result in increased lateral shoot growth. Lateral shoot growth can be undesirable as it increases canopy density. Reducing vine vigor, if possible, helps to mitigate or reduce the need for hedging. If more than two passes of hedging are normally required during a season, you should try to decrease vine vigor in subsequent seasons. Removal of lateral shoots on the main shoot can be conducted; this is done to avoid shading and to help prevent the development of secondary clusters. Depending on the training system, laterals may be beneficial if maintained on the vine, as they provide younger leaves that are more efficient in photosynthesis. Assessment of whether to remove laterals depends on your vineyard management budget as this can be an expensive operation if done with manual labor.
7. Remove late developing or excess clusters, if appropriate to your growing situation, to improve ripening and fruit quality. If done post-veraison, it should be done as soon afterward as possible to allow the vine to direct all its resources to the retained fruit. Doing the thinning at veraison also helps you determine which fruit is lagging behind as the color development is behind as well as berry size and softening (e.g., green clusters among clusters that are further along in coloring). Note that installation of bird netting largely inhibits late-season training, so all training should be done prior to netting.
Smart, Richard and Mike Robinson. 1991. Sunlight into Wine: A Handbook for Wine Grape Canopy Management. Winetitles.
Spayd, S.E., J. M. Tarara, D. L. Mee, and J. C. Ferguson. 2002. Separation of Sunlight and Temperature Effects on the Composition of Vitis vinifera cv. Merlot Berries. American Journal of Enology and Viticulture 53:171-182.
Reviewed by Bruce Bordelon, Purdue University
and Patty Skinkis, Oregon State University