jueves, 15 de mayo de 2014

Desuckering Grape Vines - Viticultural Practice


- Desuckering: Desuckenrig is the viticultural practice of removing unwanted young shoots. Known in most parts of France as épamprage, the practice is common to most vineyards of the world.

Typically, the shoots removed are either on the trunk or in the head of the vine, and grow in spring from buds surviving in the old wood. These shoots are termed water shoots and for the majority of vine varieties have no bunches of grapes.

Varieties differ in their production of water shoots; gewürz-traminer, for example, produces many, while others produce few.

The operation is carried out in spring, several weeks after budbreak, when the water shoots are 10 to 15 cm (4 to 6 in) long.

The work is relatively tiresome, as for many vineyards the shoots can be near the ground, although shoots can be removed from trunks mechanically with no damage to the trunk by mounting a rotating cylinder with rubber straps attached on the front of a tractor.

In California, desuckering is also carried out on Cordon-trained vines and so can alternatively be termed shoot thinning.

- Water Shoot: Water shoot, is a shoot that arises from the wood of the vine, not from buds left at pruning. In fact they mostly arise from basal buds embedded in the wood and are generally not fruitful. Suckers are a type of water shoot which arise at the base of the trunk at or below soil level.

- Basal buds: Basal buds or base buds, are the group of barely visible buds at the bottom of a shoot or cane. Normally they do not burst unless vines are severely pruned, and they are typically a low fruitfulness.

- Bud break: Bud break, or budburst, a stage of annual vine development during which small shoots emerge from vine buds in the spring. This process begins the new growing season and signals the end of dormancy, their period of winter sleep. The first sign that budbreak is imminent is bleeding, when the vines begin to drip water from pruning cuts. The buds left at winter pruning begin to swell in the few weeks prior to budbreak, and budbreak itself is marked by the first signs of green in the vineyard, as the first young leaves unfold and push through the bud scales.

Budbreak takes place in early spring in cool climates, when the average air temperature is about 10 °C/50 °F. For many northern hemisphere regions, budbreak occurs in March, and for the southern hemisphere in September. Budbreak is more uniform when winters are cold but not subject to winter freeze. In warm to hot regions, budbreak is earlier, and in cooler regions it is delayed. In fact in tropical viticulture the vines never achieve proper dormancy, and budbreak can take place at any time of the year.

Not all varieties show budbreak at the same temperature. For example, French studies indicate that for the early talbe grape Pearl of Csaba budbreak occurs at 5.6 °C, Merlot at 9.4 °C, and Ugni Blanc at 11.0 °C. Late pruning in winter delays budbreak, and this can be used to reduce the risk of winter frost.

In temperate regions with warm winters, a few warm days, even in midwinter, can be enough to induce bud swelling, which can lead to budbreak if the warmth persists. One of the very few places around the world to show this problem is the Margaret River region in Western Australia. Because of the nearby moderating effects of the Indian ocean, the midwinter (July) mean temperature is a warm 13 °C. Chardonnay vines are particularly prone to this premature budbreak, with only a few buds breaking on the vine in midwinter, and the rest somewhat erratically later in spring.

For vines which are properly pruned most of the buds left at winter pruning will burst, and budbreak is near 100 per cent. Budbreak is, however, normally lower for buds in the middle of long canes. (When vines are left unpruned, as in minimal pruning, it is the buds near the ends of canes which burst preferentially, as do higher buds. This adaptive physiology helped vines to climb trees and seek sunlight in their evolutionary forest habitat.) The two buds on either side of the cane just below the pruning cut typically burst. This is because of the flow of hormones in the plant and is the reason for pruning to two bud spurs.

For the vine-grower, budbreak represents the beginning of about eight months work before harvest, during which the vine must be protected from pests, vine diseases, and trained as necessary. The biggest problem for many vineyards at this time of the year is spring frost, to which the young shoot growth is particularly sensitive.

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