This year I have a couple of viticultural challenges. In the first case, I’m operating a vineyard that was planted late in the season last summer, and in the second case I have to deal with a mature vineyard that was not sprayed last year. Each vineyard presents a challenge and each has several solutions that could be applied. I’ll discuss the alternatives and then reveal what I have decided to do.
I get concerned if I have to plant a vineyard late in the spring after the weather has started to warm. The ground dries out and rainfall becomes scarce. Root development is slow and the plants remain small. I prefer to get dormant plants into the ground by the end of April and green plants into the ground by mid May. This enables maximum root development and develops strong plants for the second leaf (second growing season). If the new canes are at least a couple of metres long by fall, there should be enough root development to support a small crop in the second leaf, sufficient to generate income to cover the operating cost for the vineyard.
If there is less growth than two metres, there is the dilemma: do we save the cane and extend it with new growth or do we cut it back to two buds and develop a new cane, essentially from the ground up? If we save the cane, it will develop a shoot at each of the nodes (buds) from last season’s growth. The single trunk will become a bush unless we remove all of the unwanted new growth between the ground and the fruiting wire. If we cut it back to two buds at the base, we will develop two new canes, and the stronger one can be selected in early summer to become the new trunk for a future vine. When one of the new canes reaches beyond the fruiting wire of a VSP trellis you can remove the growing tip at the wire and this will induce laterals to grow and assist your early establishment of a bilateral cordon.
Hard as it may seem to remove most of the growth that occurred in the previous season, the better option is to cut back to two buds. If you have grafted vines, be sure that the buds are above the graft union. In reality, only one bud is required; the second is to provide a fallback in case the first is damaged. Growth during the second leaf should enable the new vine to be trained along the fruiting wire and a moderate crop to be taken during the third leaf. Always remember that the growth and development above ground is closely related to root growth below ground. If root growth is handicapped by weed competition, nutrient deficiency, or insufficient water, plant development will be suppressed.
There are many cases in which a vineyard may require remedial pruning. In a cordon pruned vineyard, old cordons eventually develop wider spacing between spurs so that the panels can’t be filled to maximize the number of canes and clusters borne in the vineyard. In other cases, a vineyard may have been damaged by a severe winter, poorly pruned, not sprayed, or may have been neglected during the previous season. Any of these situations can create a canopy in which it may be difficult to know how much old wood to remove.
In the case of a vineyard which is damaged by winter injury there are several ways to assist the recovery. A sampling of canes may be selected from throughout the vineyard and buds can be visually checked for injury. Use a razor blade or sharp knife to cut through a sampling of buds. Each node has a compound bud, with a primary bud in the centre and secondary buds on either side. In moderate injury, the primary buds can be killed and may no longer be green. The secondary buds may still be green when you cut through them. In many grape varieties, growth from secondary buds will yield a lighter crop than normal, but growth will be reasonable and the vineyard will be completely recovered by the following year. Cane viability can also be checked by soaking a sampling of canes in water to induce bud break. With severe injury, the secondary buds may be killed and cane dieback can be extensive. In this case, the best policy may be to not prune until after bud break. After the new shoots have developed three, four or more leaves, the best shoots can be selected and the vineyard can be carefully pruned. Pruning should be delayed as long as possible, because the new shoots are easily broken and manipulation during pruning can remove canes you would rather preserve.
Those of you who know me, realize that I prefer cane pruning in almost all cases, but with remedial pruning, spur pruning may be the better option. For example, in a neglected vineyard the canes are often weak and small. In this case the only viable buds may be those near the base of each cane. Select spurs that are as evenly spaced as possible along the fruiting wire. Where a space cannot be avoided, then leave longer spurs on either side. If you leave spurs with three or four nodes, then the new shoots can be fanned out to fill the void in the canopy. Be certain to leave one or two spurs as close to the head of the trunk as possible, so that renewal canes will be available in the following year to rebuild a uniform canopy.
A canopy which has been badly infected with mildew can also be a problem because the number of viable buds may not be predictable. In this case, the lower nodes on the cane may be more viable than those at the centre and tip, because they may have developed at a temperature below the optimal infection temperature for mildew. To be safe, it is a good idea to leave one or two sacrificial canes on each vine until after bud break. If growth develops in a normal fashion, the sacrificial canes can be removed. If growth is spotty, then two canes can be laid along the fruiting wire instead of one, and their viable nodes can complement each other to fill the canopy.
No one said that remedial pruning is easy. It will probably take at least twice as long to perform as normal pruning. On the other hand, if it is performed carefully, a damaged vineyard that might have produced almost no crop can be coaxed into reasonable production. That makes it all worthwhile!
This article was first published in the British Columbia Fruit Grower