Training Systems
for Premium Wine Grape Production
for Premium Wine Grape Production
Michigan State University Extension
At the recent 11th Annual Viticulture Field Day held at the Southwest Michigan Research and Extension Center (SWMREC), growers were shown five vine training systems that are currently being evaluated with regard to grape and wine production of Cabernet franc. The evaluation of experimental wine lots in this effort has been possible through the efforts of Dave Stocking in Stan Howell’s entomology program at Spartan Wine Cellars. This research, sponsored by the Michigan Grape and Wine Industry Council, will afford Michigan growers the basis upon which to make a sound decision for the production of premium grapes and wine of the Cabernet franc variety.
The production of quality wine grapes relies on two basic characteristics of the vine. The first is adequate functional leaf area, which is the source of the soluble solids that are transported to the fruit. Research indicates that generally 1.5 to two layers of leaves on a vine function well but as the layers of leaves increase, shading of the interior leaves actually becomes a detriment to vine function. Therefore, one characteristic of a good vine training system is the ability to display a large amount of leaf area in a way that all leaves are well exposed to the sun.
A second basic characteristic of a good vine training system is the exposure of fruit to the sun. This is so very important in a cool climate like Michigan because the temperature of the fruit during the period of its ripening directly influences the reduction of acid levels in the fruit. In cool growing years or when fruit develops in shade, the acid levels in wine grapes can remain too high, and therefore, reduce the quality of both the fruit and wine.
The choice of a vine training system is relatively unimportant for small vines because regardless of the choice of training system, leaves and fruit on small vines will be well exposed to sun. However, as vine size and the desire to increase yield increases, the choice of a training system can make a big difference in grape and wine quality.
Here are the five training systems we are evaluating for Cabernet franc.
Mid-wire Cordon Technique (MCT)
This is sometimes also called vertical shoot positioned (VSP) or the California sprawl, and it is the most widely used wine grape training system in several viticultural areas including California and Michigan.
This system uses a semi-permanent arm of the vine, which runs horizontally along a trellis wire (Fig. 1). This is called a cordon. Positive attributes of MCT include ease of pruning to fruiting spurs along the cordon and a minimal requirement for tying of the vine in the spring. However, there are factors that can make MCT less than ideal in some cool-climate vineyards. MCT tends to concentrate both the fruiting zone and the development of canopy along the cordon. This can increase the hazard of fruit rots for susceptible varieties. When using MCT on moderate to large vines, leaf removal in the fruiting zone should be practiced routinely to gain fruit exposure for ripening as well as to reduce the risk of fruit rot.
Modified Umbrella Kniffin (MUK)
The classic form of Umbrella Kniffin training utilizes long canes that are arched over the top wire of the trellis wire and then tied down so that the fruiting zone occurs in the top portion of the trellis.
A variation of this training system is being evaluated at SWMREC. It uses an eight-foot tall trellis so that the upper two feet collect upward-growing shoots and divert them out of the fruiting zone for better fruit exposure while still maintaining an abundance of functional leaf area (Fig. 2). A positive attribute of MUK is that it utilizes nodes on long canes that have ripened along the very top of the trellis, where the most hardy, most fruitful nodes on the vine will be found. However, a disadvantage of MUK is that the long canes must be retied to the trellis each year. Nevertheless, previous trials of MUK with Chardonnay have resulted in moderate-to-large crops of high quality fruit without the need for leaf removal.
Scott Henry (SH)
Scott Henry, a grower in the Umqua Valley of Oregon, ingeniously devised this vine training system. We are evaluating a variation of SH which employs an eight-foot trellis with two fruiting wires at 42 inches and 54 inches above ground (Fig. 3).
The shoots from the upper fruiting wire are oriented upward through a series of catch wires while those on the lower fruiting wire are oriented downward when they become long enough to be shoot positioned. The result is an open “window” in the middle of the trellis that affords excellent exposure of fruit while at the same time providing lots of leaf area in the upper and lower portions of the trellis. In many years we have found it possible to develop the upper fruiting wire as a cordon with spur pruning. That has not worked well on the lower fruiting wire, where we use a long fruiting cane.
A negative feature of SH in our experience has been the occurrence of slightly less mature fruit on the lower fruiting wire compared to the upper fruiting wire. Therefore, in our crop adjustment practices, we place two-thirds of the desired cluster number per vine in the upper fruiting zone to compensate for this difference in fruit maturity between the upper and lower fruiting wires.
Two-Tier Cordon (TTC)
This vine training system has been devised locally as a variation of the Ruakura Twin Two-Tier system which was originated in New Zealand. TTC uses two cordon-trained fruiting zones at 30 inches and 57 inches above the ground level (Fig.4). All shoots are positioned upward. They are summer pruned as the fruit begins to ripen (veraison), so that any shoots arising from the lower fruiting zone will not extend into the upper fruiting zone. Advantages of TTC include: (a) cordon training and the ability to spur prune; (b) no need for tying long canes, and (c) fruiting zones that are less congested than if there were just one fruiting zone, as in the case of mid-wire cordon. Crop adjustment with TTC is performed to place approximately two-thirds of the crop on the upper fruiting zone.
Fan training (FT)
Fan training is the most basic, least sophisticated vine training system that can be applied to a grapevine. In recent years Michigan wine grape growers have challenged themselves to grow less and less hardy wine grape varieties. When the overwintering capability of relatively tender cold-tender grapevines is in doubt, FT is an excellent way to begin managing vines.
FT simply spreads out two to four trunks from the base of the vine over the vine space (Fig. 5). These may range from relatively mature trunks to trunk renewal canes that were shoots in the previous growing season. In this way, a vine structure can be maintained even when there is a frequent occurrence of winter injury. However, disadvantages of FT include the need to tie the vine each year because the vine is pruned to long canes and the relatively poor exposure of fruit to sunlight for ripening.
To help improve fruit exposure on vines trained using FT, we have placed it on an eight-foot trellis so that much of the leaf area is caught in the upper two feet of trellis similar to that described for Modified Umbrella Kniffin training. The result has been moderately well exposed fruit when using FT. Because the population of nodes is kept relatively low on the trellis with FT, vines can readily be retrained to another vine training system if experience suggests that the vines are more winter hardy than anticipated. Therefore, FT is excellent for those who are uncertain about the long-term prospects for training their wine grapes under the cool climate conditions of Michigan.
We have superimposed on these vine training systems varying levels of cropping to understand the combined training system/crop level influence on grape and wine quality. Our evaluations of wine from these treatments have just begun. No conclusions can be made.
Nevertheless, it is noteworthy that in the early stages of our wine evaluation, some of our higher yielding treatments have at times been rated superior than those with lower yields. This is contrary to our normal expectations. However, it is not contrary to the viticultural principles that suggest that if a cluster of grapes is well exposed and has associated with it an adequate amount of leaf area, it has the potential to ripen into quality fruit. In our pursuit of grape vine training systems we seek to understand how many clusters per vine or per acre can be nurtured to produce quality fruit without any preconceived opinion as to how that number relates to an idealized optimum yield for maximum fruit quality. All theories aside, our data from this vine training system trial will document what training systems and levels of cropping can reliably produce premium wine under Michigan growing conditions.
This vine training trial is one of 10 experiments at the SWMREC that are available to viewing as a self-guided tour during all daylight hours on all days. The public is welcome to view this work in progress.
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