Manual of American Grape-Growing Part 13

REJUVENATING OLD VINES

When pruning and training are neglected, a vineyard soon becomes a sorry company of halt and maimed vines. These neglected vines can rarely be reshaped and restored to their pristine vigor. If the old vines seem capable of throwing out a strong new growth, it is almost always better to grow a new top by taking out canes from the roots and so rejuvenate. The energy and activity of Nature are seldom seen to better advantage than in these new tops, if the old tops are cut back severely and the vineyard given good care. The new canes grow with the gusto of the biblical bay tree, making it difficult oftentimes to keep them within bounds.

Usually this new top can be treated essentially as if it were a new vine. Not infrequently the cane will make sufficient growth and mature well enough so that it may be left as a permanent trunk at the end of the first season. If, however, the wood is short, weak and soft, it should be cut back in the autumn to two or three buds from one of which a permanent trunk can be trained the next season from which a good top can be formed in another season. The old top is discarded as soon as the new trunk is tied to the trellis. Old vineyards are often rejuvenated in this way to advantage and return profits to their owners for years; but if the soil is poor and the vines weak, attempts to renew the tops seldom pay.

Occasionally rejuvenating old vines by pruning is worth while. When such an attempt is made, it is best to cut back severely at the winter-pruning, leaving two, three or four canes, depending on the method of training, of six, eight or ten buds. The amount of wood left must depend on the vigor of the plant and the variety. The success of such rejuvenation depends much on selecting suitable places on the old vine from which to renew the bearing wood. It requires good judgment, considerable skill and much experience to rejuvenate successfully an old vineyard by remodeling the existing top, and if the vines are far gone with neglect it is seldom worth while.

Sometimes old vines or even a whole vineyard can be rejuvenated most easily by grafting. This is particularly true when the vines are not of the kind wanted, and when the vineyard contains an occasional stray vine from the variety to which it is planted. Directions for grafting are given on pages 45 to 50. The grafted vine is readily brought into shape, under any of the several methods of training, by treating it as a young vine.

[Ill.u.s.tration: PLATE XII.--Diana (3/5).]

CHAPTER IX

GRAPE-PRUNING ON THE PACIFIC SLOPE

The methods of pruning and training native grapes, discussed in the last two chapters, do not apply to the Vinifera grapes grown in the favored valleys of the Rocky Mountains and on the Pacific slope. As we have already seen, the Vinifera or Old World grape differs markedly in habits of growth from the American species so that it would not be expected that pruning which applies to the one would apply to the other types. The fundamentals, to be sure, are much the same and the different species of grapes are about equally subservient to the shears of the pruner, but while pruning to regulate fruit-bearing finds many similarities in Old and New World grapes, the training of the vines is radically different.

European practices in pruning and training Vinifera grapes are so many and so diverse that the first growers of this fruit in America were at a loss to know how to prune their vines. But, out of a half century of experience, American growers of Old World grapes have adapted from European practices and have devised to meet new conditions, methods which serve very well in the new home for this old grape. Since the culture of the Old World grape is centered in California, almost confined to that state, California practice may be taken as a pattern in pruning and training the vines of this species.

VINE PRUNING IN CALIFORNIA[16]

The systems of pruning in use in California may be divided into two cla.s.ses according to the arrangement of the arms on the trunk of the vine. In the commonest systems, there is a definite head to the trunk, from which all the arms arise symmetrically at nearly the same level.

The vines of these systems may be called "headed vines." In the other systems, the trunk is elongated four to eight feet and the arms are distributed regularly along the whole or the greater portion of its length. The vines of these systems, owing to the rope-like form of the trunks, are called "cordons."

The headed vines are divided according to the length of the vertical trunk into high, 2-3 feet, medium, 1-1-1/2 feet, and low, 0-6 inches.

The cordons may be vertical or horizontal, according to the direction of the trunk, which is from four to eight feet long. The horizontal cordons may be single (unilateral) or composed of two branches extending in opposite directions (bilateral). Double and even multiple vertical cordons occur, but they are very inadvisable and have no advantages.

The arrangement of the arms of a headed vine may be symmetrical in all directions at an angle of about 45 degrees. Such a vine is said to be "vase-formed," though the hollow center which this term implies is not essential. This is the form used in the great majority of our vineyards whether of wine, raisin, or shipping grapes. It is suitable for the "square" system of planting and cross cultivation. Where vines are planted in the avenue system, particularly when trellised and where cross cultivation is impossible, the arms are given a "fan-shaped" arrangement in a vertical plane. This arrangement is considered to be essential for the economical and easy working of trellised vines.

On the vertical or upright cordon, the arms are arranged at as regular intervals as possible on all sides of the trunk from the top to within twelve or fifteen inches of the bottom. On the horizontal cordon the arms are arranged similarly, but as nearly as possible on the upper side of the trunk only.

Each of these systems may again be divided into two subsystems, according to the management of the annual growth or canes. In one, spurs of one, two, or three eyes are left for fruit production. This system is called short or spur pruning. In the other, long canes are left for fruit production. This is called long or cane pruning. In rare cases an intermediate form is adopted in which long spurs or short canes of five or six eyes are left. In cane pruning, each fruit cane is accompanied by one or two short renewal spurs. These must also accompany half-long pruning. Systems of pruning, when only long canes are left without renewal-spurs, are not in use in California. In all systems, replacing-spurs are left wherever and whenever needed.

Other modifications are introduced by the manner of disposal of the fruit canes. These may be tied up vertically to a stake driven at the foot of each vine or bowed in a circle and tied to this same stake, or they may be tied laterally to wires stretching along the rows in a horizontal, ascending or descending direction.

The different systems differ therefore in: (1) the shape, length, and direction of the trunk; (2) the arrangement of the arms; (3) the use of fruit spurs or fruit canes with renewal spurs; (4) the disposal of the fruit canes.

The princ.i.p.al possibilities of the pruning are shown in the following table:

A. HEAD PRUNING: VASE-FORM

} { (_a_) Fruit spurs or } { 1. High trunk: } { (_b_) Half-long canes and renewal } { spurs or 2. Medium trunk: } with { } { (_c_) Fruit canes and renewal 3. Low trunk: } { spurs; canes vertical } { or bowed.

B. HEAD PRUNING: FAN-SHAPED; TRELLISED

1. High trunk: Fruit canes and renewal spurs; canes descending.

2. Medium trunk: Fruit canes and renewal spurs; canes horizontal or ascending.

C. CORDON PRUNING

1. Vertical: Spur; half-long; cane.

2. Horizontal-unilateral: Spur; half-long; cane.

3. Horizontal-bilateral: Spur; half-long; cane.

All possible combinations indicated by this table represent 24 variations. Some of these combinations, however, are not used and some are rare. The most common are shown in Figs. 23, 24, 25, 26 and 27.

Figure 23 B represents a headed, vase-formed vine, with a medium trunk and short fruit spurs. This is the most common system used in all parts of California and is suited for all small growing vines which bear on the lower buds, for most wine grapes and for Muscats. The unit of pruning in this case is a fruit spur of 1, 2, or 3 internodes, according to the vigor of the variety and of the individual cane.

Figure 23 A differs from 23 B only in the higher trunk and longer arms. It is commonly used for Tokay and other large growing varieties, especially when growing in rich soil and when planted far apart.

[Ill.u.s.tration: FIG. 23. Forms of head pruning: _A_, spur pruning with high trunk; _B_, spur pruning with medium trunk; _C_, half-long with medium trunk.]

Figure 23 C has the same form of body as A and B, except that the arms are somewhat less numerous. The unit of pruning is a short fruit cane of four to five internodes, accompanied by a renewal spur of one internode. It is suited for vigorous table grapes, which do not bear well on short spurs. It is used especially for the Cornichon and Malaga in rich soil. This is a difficult system to keep in good shape owing to the tendency for all the vigor to go to the growth on the ends of the fruit canes. It is difficult to obtain vigorous canes on the renewal spurs. Occasional short pruning is usually necessary to keep the vines in proper shape.

Figure 24 A is similar to 23 C in form, but the number of arms is still further reduced to 2, 3, or at most 4. The unit of pruning is a fruit cane of 2-1/2 to 3-1/2 feet with its renewal spur. Owing to the length of the fruit canes they require support and are tied to a high stake.

This method is used in a large number of vineyards with Sultanina, Sultana and certain wine grapes, especially Semillon and Cabernet. It is not to be recommended in any case, as it has several very serious defects.

The difficulty of obtaining new wood from the renewal spurs is even greater than in the system shown in Fig. 23 C. The length and vertical position of the fruit canes cause the main growth and vigor of the vine to be expended on the highest shoots. The renewal spurs are thus so shaded that, even though their buds start, the shoots make but a weak growth. The result is that at the following pruning all the good new wood is at the top of the fruit canes of the previous year, where it cannot be utilized. The pruner has to choose then between reverting to spur pruning and getting no crop or using the weak growth from the renewal spurs for fruit canes, in which case he may get blossoms but little or no fruit of any value.

[Ill.u.s.tration: FIG. 24. Forms of head pruning: _A_, vertical fruit canes and renewal spurs; _B_, bowed fruit canes and renewal spurs.]

Other defects of this method are that the fruiting shoots are excessively vigorous and therefore often tend to drop their blossoms without setting and the fruit when produced is ma.s.sed together so that it ripens unevenly and is difficult to gather. It also requires a tall and expensive stake.

Figure 24 B represents an improvement on the last system. It differs only in the method of treating the fruit canes. These are bent over in the form of a circle and tied by their middle part to a stake which may be smaller and lower than that needed for the vertical canes.

This bowing of the canes has several useful effects. The change of direction moderates the tendency of the vigor of the vine to expend itself only on the terminal shoots. More shoots therefore are formed on the fruit canes and as their vigor is somewhat decreased they tend to be more fruitful. The slight mechanical injury caused by the bending operates in the same direction.

[Ill.u.s.tration: FIG. 25. Head pruning: fan-shaped head; fruit canes tied to horizontal trellis.]

The excess of vigor thus being diverted from the fruit canes causes the renewal spurs to form vigorous shoots, which soon grow above the fruit shoots and obtain the light and air they need for their proper development. This method is used successfully for certain wine grapes such as Riesling, Cabernet, and Semillon. It is unsuited to large vigorous varieties or for vines on rich soil planted wide apart. In these cases two fruit canes are usually insufficient and, if more are used, the grapes and leaves are so ma.s.sed together that they are subject to mildew and do not ripen evenly or well. The bowing and tying of the canes requires considerable skill and care on the part of the workmen.

The body, arms, and annual pruning of the system shown in Fig. 25 are similar to those of Fig. 24, with the exception that the arms are given a fan-shaped arrangement in one plane. It differs in the disposal of the fruit canes, which are supported by a trellis stretching along the row from vine to vine.

This method is largely used for the Sultanina (Thompson's Seedless), and is the best system for vigorous vines which require long pruning, wherever it is possible to dispense with cross cultivation. It is also suitable for any long-pruned varieties when growing in very fertile soil.

Figure 26 is a photograph of a four-year-old Emperor vine, ill.u.s.trating the vertical cordon system. It consists of an upright trunk 4-1/2 feet high with short arms and fruit spurs scattered evenly and symmetrically from the top to within fifteen inches of the bottom.

This system is used in many Emperor vineyards in the San Joaquin Valley.