throughout the season will produce a more uniform and predictable yield. Some varieties such as muscats or table grapes have a predisposition toward incompletely formed lower buds during spring growth of next season’s fruiting wood.
The most reliable indicator of trunk injury is that vines push an abnormally large number of vigorous shoots from the base.
In this case there is sufficient damage to the xylem layer under the bark that latent buds at the base of the trunk are activated. Even though there may still be weak growth on the top of the vine, it will most likely be sporadic and low yielding.
The chances of full recovery of a vine after trunk injury are slim. Select a couple of strong new canes and train them up to the wire. When you next winter-prune, the old trunk can be removed and the strongest cane can be trained as a replacement. If your vineyard has grafted vines, pay attention to the leaf pattern to ensure that you are not selecting a rootstock instead of a scion. Remove any rootstock shoots while you can still identify them. There are differences in wood appearance but leaf identification is much easier. Another fairly common situation is that normal budbreak occurs and cane growth is initiated but the vines appear to have a moisture deficit as soon as warm weather occurs. This is typically caused by some form of injury that handicaps water uptake. This may be less severe trunk injury than described above or it may be root damage. Root damage can occur in several ways.
A common vineyard management strategy in a semi arid area such as the Okanagan is to irrigate heavily at the end of the growing season, just before irrigation systems are blown out for winter. The elevated soil moisture content increases the specific heat of soil and minimizes frost penetration into the root zone. The risk of freezing injury to roots is also minimized by well-matured vines with good carbohydrate reserves, snow cover, adequate organic matter in the soil, finer particle soils, mycorrhizal synergy, and well rooted cover crops. Each of these contributes its increment to minimize frost penetration and guard against freezing injury to vine roots.
When vines leaf out and initiate
normal growth but wilt around the time of bloom, there is probably root damage. In some cases it may be a fungal infection. Fungal infections typically will be in
a small area of the vineyard, whereas winter injury to roots will be more general. By the time visible symptoms appear, it may be too late to save the vines. If there are mild symptoms, removal of extra foliage may enable the vine to take up enough water to support the reduced leaf area, but
don’t lay any wagers.
Northern vineyards have the potential to produce great wines with varietal character and balance that are difficult to achieve at lower latitudes. On the other hand, we should never forget that grapes are not native to this region. It is up to us to provide supportive conditions to enable their survival when the weather doesn’t cooperate.
— Gary Strachan can be reached at
gestrachan@alum.mit.edu
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www.VintageNurseries.com Serving the Wine, Table Grape and Raisin Industries 21
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