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Winter Cold Inury to Grapevine Canes & TrunksStrategies to Tolerate Frequent Cold Injury to Trunks |
Strategies for living with cold damage injury to canes and trunks
Sooner or later most vineyards in cool climates will suffer cold injury. Spring freeze is the most common, but I have seen cane and trunk cold injury in California and Australia, certainly not places associated with cold winters. In northern Europe growers in such historic areas as Champagne, Chianti and the Rhinegau can expect to have vines killed to the ground by winter cold injury at least once or twice a generation. Thus every grower might consider how he should treat vines which have been cold damaged.
The big difference between COLD climates and cool climates is that grape growers in cold climates can assume that cold damage may be the rule rather than the exception. The cold climate grape grower should be prepared to not only grow vines that tolerate cold stress, he/she should practice a viticulture which tolerates cold injury to vines.
Grower endurance
By far the most common strategy to deal with cold injury is grower tolerance, not vine tolerance. Even in the coolest European grape growing regions the expected frequency of cold damage is small enough that growers do not resort to special treatments which complicate management and certainly increase the annual expense of grape growing. The growers are prepared to endure the damage. When their vines are injured they have the choice of retraining new vines from sucker growth or replacing the injured vines.
Multiple trunks
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A Chardonnay vine trained to endure winter cold injury. Note multiple trunks of various ages and the high number of retained canes and buds. At this stage of development the number of canes and/or growing shoots can be adjusted to a "normal" target number. Even though there has been some cold bud injury (note buds which did not produce shoots), sufficient buds did survive to produce a normal crop. |
Multiple trunks are one part a system for surviving cold injury sometimes refered to as 'Spare Parts Viticulture'. In areas where one must be prepared to endure cold damage as well as cold stress, it seems wise to have extra plant parts in place. One hopes that some of the parts will escape injury even when others do not.
The figure shows a vine with multiple trunks. There are four trunks of at least three different ages. The two large trunks are more than 3 years old. Another trunk was formed by tying up a sucker originating near the graft union two summers previous to the winter the picture was taken. The youngest trunk is a cane which developed from a sucker shoot tied up in the previous growing season. When (if) some of the older trunks show signs of winter cold injury, they can be removed and the remaining trunks can bear a full crop.
The figure also shows some of the complications of this approach. First the large number of canes and trunks require a large amount of space. As a result, otherwise desirable training systems such as cordon or vertically shoot positioned training become difficult. The many trunks can interfere with machine harvesters. The collecting plates remain open too long and some fruit may be lost to the ground. Finally there is a matter of labor and materials expense. The multiple trunks slow pruning, and the shoots required to develop new trunks must be trained in the summer.
Suckering is also made more complicated by the need to retain growth at the base of the vine. When growers are meticulous about removing unwanted shoot growth from the base of the vine for the first 2-3 years of vineyard life, the tendency for sucker development in future years is minimized. In the long run suckering cost is minimized. However, this approach will not work for multiple trunked vines. The grower needs a continuous supply of suckers to form new shoots. This also means he/she has a more expensive yearly task of removing suckers not wanted for trunks. The need to retain green shoot growth at the base of the trunk also makes weed control by post-emergent herbicides, such as round-up (glyphosate), more difficult.
TRAINING MULTIPLE TRUNKS
If a multiple trunk vine is desired, then little shoot pruning is done at planting, and 4-8 shoots are encouraged to grow. Usually they are trained to a low wire. Many shoots are retained because regions with cold winters also usually have short summers. The goal is to get maximum early season leaf area development, and to avoid excessively vigorous shoot growth which might not mature in a short season. For the second season the longest, best placed cane is tied up, and 4-8 shoots arising high on the cane are allowed to develope. During that second growing season one or two shoots arising near the ground (make sure they are not shoots of the rootstock variety) are retained and tied up. During the following winter, canes appropriate for the training system are retained from the older trunk, and the new trunk is shortened to an appropriate head height. Often a spur is left near the ground to produce new shoots, although this isn't really necessary so long as the vine bases are not kept completey free of shoots in future years.
When grow tubes are used, retaining many shoots in the first year may not be feasible, but new trunks can usually be formed after the grow tubes are removed.
SUMMARY
Cold season grape growers have to expect cold injury to buds, canes and trunks. Buds develop as individuals and there are usually a surplus produced in any one year. However, trunks and canes have to support major portions of the vine, and injury is more serious. Understanding which tissues become injured and the impact of the injury can provide growers with information needed to make good decisions about cold injured grapevines. When injury is expected even when vine growth is optimized, then an approach which ensures that spare parts are available to replace injured vines parts may be an economic approach.
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