Within a given cultivar, darker colored canes indicate good light exposure during the previous growing season and greater bud fruitfulness. Buds from these canes will also be more winter hardy. Bull canes are poorly exposed, highly vigorous shoots with low hardiness and low productivity. The relationship between large cane diameter and bud fruitfulness and hardiness has not been precisely determined for French hybrid and Vitis vinifera cultivars. Large diameter canes frequently have persistent laterals.
Persistent laterals are side branches on a shoot that mature as shoots and become canes.
The retention of persistent laterals is desirable for all V. labruscana cultivars. The bud on the lateral is more fruitful than the bud at the node where the persistent lateral has developed. Do not select canes possessing persistent laterals for tender cultivars, however, because the canes are less cold resistant than medium diameter canes that have no persistent laterals. When to Prune Grapevines may be pruned anytime during the dormant season. Pruned vines are more easily damaged by a cold stress episode than unpruned vines, however, and once vines are pruned, bud number cannot be modified to compensate for losses due to winter cold damage.