|EFFECT OF PRUNING ON VINES | TRAINING -PRUNING SYSTEMS | PRUNING MATURE VINES | PRUNING TOOLS | SUMMER PRUNING|
Pruning refers to the removal of canes, shoots, leaves, and other vegetative parts of the vine. The three main objectives of pruning are as follows:
LENGTH OF BEARING UNITS
This is defined by the fruiting habit of the variety-by the fruitfulness of the buds on the cane and the size of the clusters produced. Usually spur pruning is used on varieties having large clusters and to the base of the cane, and cane pruning is used on small clusters or those in which buds on the basal portion 1.
Effects of Pruning on vine behavior
One must be acquainted with the following pruning relationships to understand the recommendations for pruning:
TYPES OF TRAINING-PRUNING SYSTEMS
The different pruning-training systems worldwide are innumerabl. In California the main systems are head-trained-spur pruned, cordon-trained-spur pruned, and head-trained-cane pruned.
Head Training-Spur Pruning
The vine has the shape of a small upright shrub, with a vertical trunk (0.30 0.91 m) high that supports arms spaced around its head. At winter pruning, spurs are left to produce the shoots that will bear the next crop and furnish canes for the following year's spurs. Head training is used on many wine grapes. Its' advantages are simplicity of shape, ease of training, inexpensive to establish, and it does not require a wire trellis. Short stakes are required for about 10 years, or until trunks are rigid enough to be self-supporting. Cross-cultivation is possible to help in controlling noxious weeds. Disadvantages of the head system are that it requires severe pruning which depresses the growth of the vine, and vines are slow to come into full production. The fruit often masses within a small area, causing bunch rot and poorer colour on some varieties.
Cordon Training-Spur Pruning
The trunk of the bilateral, horizontal cordon rises vertically to about 812 in. (20.3-30.5 cm) below the lower wire of the trellis, and then divides into two branches that extend in opposite directions along the lower wire to within about 10 in. (25.4 cm) of the adjacent vines. The bends should be smooth and regular, and the branches should be straight. Shoots or spurs should not be retained at the bend of mature vines because they will become very vigorous and shade out the other spurs. Bearing units are spurs on small arms located at regular intervals on the horizontal branches (cordons). Spurs should be located on the upper surface of the cordons.
Advantages of the cordon system are that fruit is well distributed, hangs at about the same level from the ground, and usually colours well. This system is well adapted to mechanical harvest. Disadvantages are 'that it is laborious and costly to establish, and permanent support is required. It is well adapted for table grapes and large-clustered wine grapes.
Head Training-Cone Pruning
The shape is similar to that of head-trained vines, except that the head may be fan-shaped in the plane of the trellis. Only two or three arms on each side of the head are usually needed. At winter pruning, fruit canes with 8 to 15 buds [2-4 ft (0.61-1.22 m) long] are retained for fruit production and old fruit canes are removed. Canes for use the following year are produced from the 3 or 4 renewal spurs (usually 2 buds long) retained in the head of the vine. Occasionally growers leave no renewal spurs because ample shoots develop from basal buds of the canes in some vineyards.
Advantages of cane pruning are that a full crop is obtained for varieties that have few or no fruitful buds near the base of the cane, such as in Thompson Seedless. A larger crop can be obtained for very small-clustered wine varieties such as Cabernet Sauvignon, Whit Riesling, and Sauvignon blanc, and the fruit is well distributed. Disadvantages of cane pruning include the tendency of most varieties to overcrop fruit and the high cost of pruning and tying canes. A trellis is required.
TECHNIQUE OF PRUNING MATURE VINES
Head Training-Spur Pruning
Vines should be pruned according to their capacity. In head-trained spur-pruned vines, the number and length of spurs left the previous year, the size of the canes, and the number of clusters produced during the current season may be used as a guide in determining the number and length of spurs to retain. The number of clusters produced may be determined by counting the stubs remaining where the clusters were cut off. A vine with canes of normal size that produced a good crop should be pruned to about the same number of spurs of similar length, as measured by the number of buds, as the previous year. If canes are larger than normal, they should be pruned less severely, leaving more or longer spurs or both, so that the vine capacity can be used fully for fruit production. Weaker than normal vines should be pruned more severely, leaving fewer buds, by retaining fewer or shorter spurs or both.
Spurs from vigorous canes should have more buds than those from weak canes. Basal buds, 6.35 mm or closer to the base of the cane, should not be counted. Pencil-size canes should be cut back to I bud, and thumb-sized ones to 3 or 4 buds. The best canes are often the 2 or 3-bud spurs of intermediate size. A more exact method of determining capacity is to prune the vine and weigh the pruning brush. The number of buds to be retained is proportional to the weight of brush.
Cordon Training-Spur Pruning
Cordon-trained vines are pruned to spurs, and the same techniques are used as for head training-spur pruning.
Head Training - Cane Pruning
In the dormant season there are several canes that have usually arisen from renewaI spurs, from basal buds, or from old wood. Select the strong canes and prune off the weak ones. If two good canes arise from a renewal spur, use the apical one for the cane, and cut the lower a renewal spur. Large canes of 12.7 mm or greater diameter can be pruned to 15 buds, but smaller canes must be pruned shorter. For table grape production where thinning is used, one can leave a number of canes. Renewal spurs, usually one per cane, should be placed in the best positions to maintain proper shape of the vine, some growers find renewal spurs are unnecessary.
Summer pruning consists of the removal of green vegetative tissues during season and includes suckering, pinching, topping, and leaf removal. Suckering is the removal of water sprouts from the trunk and below the soil surface. It should be performed several times each e vines are young and at least once a year on older vines. Crown Suckering, the removal of water sprouts from the branches and arms, should be done early when shoots are about 7.62-15.2 cm long. Its purpose is to improve the quality of the fruit or to direct growth into other vine parts, and it can cause considerable fruit thinning. Crown suckering is useful on shoots of varieties that produce sprouts, such as Muscat of Alexandria. Sufficient sprouts must be retained to shade the head of the vine and its clusters.
Pinching refers to the removal of the growing tip, and is used to decrease wind damage and to train young vines.
Topping is the removal of the apical (30.5-60.9 cm) of a shoot. It provides protection against the wind, but the loss of foliage can greatly weaken the vine.
Leaf removal is often performed on varieties such as Tokay and Emperor to enhance fruit coloration. Leaves are usually removed in June in the cluster area, to allow more light to enter, prevent rubbing of the fruit by leaves, and to facilitate harvest. Cardinal and Ribier are quite similar in growth and fruiting characteristics and require extensive hand labour for crown suckering, flowering, lateral shoot removal, removal of shoulders on retained clusters, and removal of leaves for fruit exposure. This must be done at early prebloom when lateral shoots are still tender and easy to remove.
There are usually one, two, or three clusters per shoot on Cardinal and Ribier. Where there are three clusters, growers usually remove the basal cluster, take off the wing on the middle cluster, and remove the tendril of the apical cluster if present. It is common practice to remove the large basal leaves; lateral shoots must also be removed while they are small. Some growers take off the leaves and lateral shoots from the apical cluster to the base of the shoot.
Two basal leaves can be removed without adverse effects, but removal of all leaves from the apical cluster downward greatly reduces the yield of packable fruit, because of a poor set of berries that result in straggly clusters with many shot berries (Jensen et al., 1975).
TOOLS FOR PRUNING
Pruning shears are usually used for pruning. One-handed
shears are suitable for smaller vines, but two-handed shears are more appropriate for large ones. Pneumatic air systems, a simpler and more rapid method, are also used for pruning. With this technique, an air reservoir with air under pressure is connected to the pruning shears of pruners by air lines on a boom. By this method several rows can be pruned at the same time from one power source. Another pruning aid is a machine called a hedger, which can trim off many canes on the tops and sides of the vines, and thus simplify the of the hand pruning. Another machine can trim off a portion of the en shoots on the sides of the vines in summer, a task often performed re harvest to facilitate picking and make entrance into the vineyard easier.