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 21/2 to 31/2 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.
Fig. 24. Forms of head pruning: A, vertical fruit canes and renewal spurs; B, bowed fruit canes and renewal spurs.