Shoot Positioning

Vine canopy management is a key factor in producing quality table grapes in a temperate climate. It begins with the choice of a vine training system. Fan training is presented in this publication only because it is a reasonable option for those determined to grow grapes in a marginal vineyard site that is vulnerable to frequent winter injury to vines. All of the other vine training systems in this publication were chosen because they are compatible with the canopy management practice of shoot positioning. Shoots of grapevines tend to grow upward and then run along the top of a vineyard trellis. In warm climates, the entangled mass of shoot growth at the top of the trellis is often considered desirable because it shades fruit to prevent sunscald. In temperate-climate vineyards, there is less risk of sunscald. The primary challenge is fruit maturation. Fruit exposure to the sun promotes fruit maturation in two ways. First, as the fruit begins to ripen and change color, a time viticulturists call veraison, the metabolism of acids in the berries is profoundly influenced by the temperature of the fruit. Generally, higher fruit temperatures from exposure to the sun will result in lower acid levels in the fruit. Secondly, when clusters are well exposed to the sun, so are the leaves close to those clusters. That results in more efficient production of sugar in the leaves, which is then transferred to the fruit. The combination of decreased acid and increased sugars is what makes the fruit taste good! Shoot positioning is a vine canopy management tool to achieve the desirable sun exposure of table grapes in a temperate climate. Rather than allowing shoots to pile up in multiple layers in a random arrangement at the top of the trellis, the grower systematically places shoots where they have sunlight-exposed, functional leaves that do not densely shade the fruit. This task is begun early in the growing season, usually about the time of bloom. It is time to begin shoot positioning when shoots have a firm attachment to the cane so they aren't easily detached while being moved, there is only a small amount of tendril attachment to the trellis, and the majority of shoots are long enough and heavy enough to remain in their new orientation — i.e., they don't "spring back" to their original orientation. There is no harm to fruit set if this task is performed during bloom. Shoot positioning table grapes in a temperate climate moves shoots away from the top of the trellis so they hang down on the sides of the trellis, thus exposing the fruit at the top of the trellis. For example, with the modified Munson training system, shoots are moved from a running orientation along the top of the trellis (Fig. 12) so they bend over the outer catch wires and then hang vertically toward the ground (Fig. 13). In that orientation, the clusters as well as the leaves near the clusters are well exposed to sun. The skill to gently break tendril attachments and move shoots off the top of the trellis is easily and quickly learned. If movable arms are used to support the catch wires (Fig. 12), they can be lowered at the time of dormant pruning and then raised again after the first time of shoot positioning. The movable arms make the job of shoot positioning easier. A second time of shoot positioning about two weeks after the first is necessary to

Section IV -

Special Practices to Produce Quality Table Grapes finish orientation of shoots that were too short to manipulate in the first pass. Shoots originating from renewal spurs or other places lower on the vine should also be positioned down and away from the fruit zone (Fig.le). This task is most efficiently performed in pairs with one person on each side of the trellis. Prevailing westerly winds often push the majority of shoots to the east side of north-south-oriented trellises. To the extent possible, shoot positioning should counteract that tendency by placing as many shoots on the west side of the trellis as possible. Shoot positioning of vines trained to the Hudson River umbrella (Fig. 1e) and modified 4-arm Kniffin training systems (Fig. 3c) orients shoots vertically down the sides of the trellis.

If a grower is unable to shoot position at the optimum time, it should still be done later. Late shoot positioning has two penalties however. First, the task becomes considerably more difficult. Tendrils may have to be cut rather than simply pulled apart. Secondly, if the fruit develops too long in the shade, it may be vulnerable to sunscald, depending on the variety and the weather conditions.

Shoot positioning not only promotes fruit maturity but also creates a better, more open target for pesticide applications, reduces the susceptibility of the vine to several diseases, facilitates both hand harvesting and pruning the next winter, and promotes the fruitfulness of nodes in the renewal zone for the following growing season. This vineyard task should be a high priority for every grower of table grapes in a temperate climate.

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