Pruning and training are perhaps the most important cultural management practices for grapes. A thorough understanding of the concepts of pruning severity and crop load is critical to sustained production of high-quality fruit.
Pruning and training of young grapevines are done to establish a vine form that meets the requirements of the training system. The grower should decide which training system to use prior to planting the vineyard. The information presented here will assume that the vines will be trained to a high cordon (HC) system, the most common training system for American and French hybrid wine grapes in the Midwest. Growers planning to use other training systems will need to make modifications to these directions.
Good vine growth during the first two years is critical to the future performance of the vineyard. Vines that do not establish well due to poor cultural management are usually set back several years. One main goal is to establish a large healthy root system by promoting maximum amounts of healthy, well-exposed foliage. To accomplish this goal during the first two years, care must be taken to train vines properly, control weeds, provide necessary nutrients, and control diseases and insects.
Once vines are planted, the grower has several options for pruning and training the vines. Support should be provided for young vines to keep them off the ground. This will greatly reduce disease problems and provide full sun exposure for maximum growth.
The trellis can be established soon after planting to provide this support. If the trellis cannot be established during the planting year, then a single stake should be driven next to each plant, and the shoots tied to the stake. Though it is not necessary to establish the trellis during the planting year, doing so greatly facilitates vine training. (See Figure 24.)
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| FIGURE 24. Establishing the trellis during the planting year facilitates vine training. |
Proper training begins during the year of planting, and the goal is to develop strong, straight shoots that are long enough to be retained as trunks for the second growing season. Shoot vigor is directly related to management of weeds and fertility. If weeds are controlled and if the vines receive adequate nitrogen fertilizer, then they should produce several shoots capable of reaching the top wire of the trellis system.
In this case, the vines can be left unpruned, or pruned to six to eight buds after planting. Vines left unpruned will develop more functional leaf area and larger root systems than vines pruned to a small number of growing shoots.
If, however, the grower is not prepared to adequately control weeds and provide needed nutrients, then unpruned vines are likely to produce several short shoots, none of which will be long enough to retain as trunks at the start of the second year. In this case, vines should be pruned to a few buds and all growth removed, except the two strongest shoots. This should assure that at least one shoot will be long enough to retain as a trunk.
Generally, mistakes are made by rushing vineyard establishment when growers are not fully committed to good vineyard management. In this case, it is recommended that vineyard establishment be delayed until a commitment can be made.
In recent years, grow tubes, or vine shelters, have become popular for vineyard establishment (Figure 25). These plastic tubes create a greenhouse-like environment around the plant that promotes rapid shoot growth early in the season. This early rapid growth usually results in a single dominant shoot that has long internodes and is very straight.
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| FIGURE 25. Grow tubes used after grapevine planting during the establishment year. |
Proponents claim increased first-year vine growth and subsequent earlier production, with vines being capable of producing a crop in the second growing season. However, little scientific evidence supports these claims.
Research in the Midwest has not shown an overall growth increase in vines from using grow tubes. Though tubed vines grow faster early in the season, by the end of the season there is no difference in vine size between tubed and un-tubed vines. In addition, research has shown that restricting growth to a single shoot, whether by use of a grow tube or by pruning alone, also reduces overall vine growth.
In a recent study, we found that vines left unpruned and allowed to develop six to eight shoots developed three times more total leaf area than vines trained to a single shoot (tubed or un-tubed) and, more importantly, had at least twice as much root dry weight. The difference in root system size is especially critical since one of the primary goals in vineyard establishment is development of a large healthy root system.
A strong correlation was shown between total leaf area and root dry weight, which suggests that growers should try to maximize leaf area during vineyard establishment. In most cases, the use of grow tubes will lead to reduced leaf area during the first growing season.
The primary advantage of using grow tubes in the Midwest appears to be protection from broad-spectrum contact herbicides, such as glyphosate and paraquat, and animal depredation and a reduction in the time needed for early-season vine training. However, the time saving is generally offset by the labor required to install and remove the tubes.
Protection of vines from post-emergent herbicides allows the grower to apply broad-spectrum herbicides easily and safely with conventional spraying equipment. Good weed control is critical for achieving acceptable vine growth, so this offers an advantage.
Grow tubes also keep the vines off the ground with minimal tying required during the first few weeks of growth. However, once the shoots grow out of the top of the tube, they must be tied to a string or a stake to prevent damage from wind blowing them across the top of the tube. Grow tubes must be removed in mid-August to early September to promote hardening of the new growth and aid in winter survival.
During the second year, the primary goal is much the same as the first year—maximizing vegetative growth. Weed management and nutrition are again critical for acceptable vine growth.
At the start of the second year, canes of the previous year’s growth will be retained to be the trunk(s). It is important to retain only healthy canes that are free of mechanical damage or winter injury, if the vine is to have good strong trunks that will be productive and healthy for several years. Additionally, the straightness of the trunks is determined at this time. Not only are straight trunks more esthetically pleasing, they are also easier to manage, especially if mechanized pruning and harvesting are planned.
One method to ensure straight trunks is to cut the cane off about 4 inches shorter than the top wire, tie a short piece of twine to the end of the cane and secure it tightly to the tensioned top wire. (Note: The top wire must be tensioned at the start of the second season).
A second method is to tie a piece of twine from a spur at the base of the vine to the top wire. The cane is then gently wound around the piece of twine and tied to the top wire. Bamboo or wood stakes can also be used to train straight trunks, but they increase cost.
If a double trunk system is desired, then two canes are retained as trunks. If possible, the two canes should originate from below ground. Proper planting depth of own-rooted vines will encourage development of shoots from below the ground surface. On grafted vines (all European vinifera cultivars are grafted onto Phylloxera-resistant rootstocks and some hybrids are grafted to increase vigor), the shoots must originate from above the graft union, and the graft union must remain above the soil line to prevent scion rooting.
If double trunks are desired, but there is only one cane of sufficient length and quality to retain as a trunk, then a shoot can be retained from the base of the vine during the second growing season. If none of the first-year canes is of sufficient length to reach the top wire, then the vine should be cut back to six to eight buds and handled as a first-year vine.
In addition to establishing the trunks, the cordons will be developed during the second season. Shoots are retained at the appropriate position and trained along the top wire. On moderately vigorous vines, thin to the best two to four shoots at the top of the trunks. On more vigorous vines, several shoots can be retained above the middle wire to increase the total leaf area. All shoots below the middle wire should be removed unless one is to be retained as a second trunk.
Some growers like to pinch the tips when these shoots reach the appropriate cordon length (4 ft. for 8-ft.-spaced vines). This promotes lateral branching and early development of spurs on the future cordon. However, some growers prefer to let the shoots grow full length and cut them back to the appropriate length at the beginning of the third season.
At the beginning of the third season, the best canes are retained to be the cordons. Other canes are cut back to renewal spurs or completely removed. If pencil-size lateral shoots are present on the cane and have persisted—are healthy and not winter damaged—they can be cut back to one- to two-node spurs. If laterals are not present or are too small, the “canes to be cordons” should be cut back to two-feet long (for a four-foot long cordon) or a 10-node cane (whichever is the shortest). This practice minimizes the negative impact of apical dominance, which thus promotes uniform bud break and shoot growth along the cordons. It also reduces the frequency of blind nodes on cordons in subsequent years. The extension of the cordon is established in the following season.
The new cordons should be loosely wrapped about one full turn over the top wire. Securely attach the end of the cordon to the top wire with wire twist ties and loosely attach the base of the cordon to the top wire with plastic chain-lock or similar ties that are strong but loose. The cordon should be wrapped loosely around the top wire so there is room for it to expand over time.
Many growers reverse the direction that they wrap the cordon on each side of the vine to reduce the chances that the vine will unwind. That is, the cordon on one side of the vine is wrapped over then under the wire, and the cordon on the other side is wrapped under then over the wire.
The primary purpose in pruning mature grapevines (four years and older) is to balance the amount of crop produced to the vine’s capacity to ripen the crop. Understanding the relationship between pruning, yield, and vine vigor is a necessity for the grape grower.
Pruning modifies the size and form of the vine, making it possible to produce more high-quality fruit. At the same time, pruning helps the vine maintain adequate vegetative vigor for high yields in future crops. If training efforts during the first two years have been successful, the third-year vine is fully formed and trained for the desired training system. Consequently, the pruning procedure for a three-year-old vine is essentially the same as for a mature vine.
The wood remaining after pruning in the third season is used to produce the crop. The amount or extent of pruning is done in proportion to the amount of wood produced in the second growing season, or vine vigor. The same principle applies in the fourth and all consecutive seasons. Additional information is presented in Balanced Pruning on page 44.
By today’s standards, a good mature Concord vineyard is capable of producing six or more tons of grapes per acre. If the vines are planted 8 feet apart in the row with 10 feet between rows, there will be 545 vines per acre. This means the average yield must be at least 22 pounds per vine. An average cluster of grapes usually weighs 3 to 4 ounces. Therefore, 80 to 100 clusters per vine are needed to produce 22 pounds of fruit. Because each fruit-bearing shoot produces one to three clusters, 40 to 50 shoots per vine can produce the crop.
A single shoot arises from a bud, but not all shoots flower and set fruit. Consequently, more than 50 buds per vine may be necessary to produce the 6-ton crop. French hybrids and vinifera cultivars differ from Concord; however, the principles are the same. Refer to Table 7 for average cluster weight so that adjustments can be made in cluster number and, subsequently, bud number.
The mature grapevine will have several hundred buds before pruning, and more than half are capable of producing fruiting shoots. If all buds remain, the vine will overcrop, resulting in delayed fruit maturity, small berries, and small clusters. More important, the vine will not produce enough good fruiting wood for the next year’s crop. On the other hand, if the vine is over-pruned, the current season’s crop will be reduced, and new growth may be overly vigorous. Excessively vigorous growth produces poor fruiting wood for the following season.
| Table 7. Approximate Number of Clusters per Vine for Different Cluster Sizes and Crop Yields. (Based on 8 x 10 spacing, 545 vines/acre). | |||
| Cluster Size | 4 Tons/Acre | 6 Tons/Acre | 8 Tons/Acre |
|---|---|---|---|
| Large Clusters (1 lb) | 15 | 22 | 30 |
| Medium Clusters (1/2 lb) | 30 | 44 | 60 |
| Small Clusters (1/4 lb) | 60 | 88 | 90 |
Grapevines can be pruned throughout the dormant season. However, fall-pruned vines are more prone to winter injury than those left unpruned. Growers should wait until late winter or early spring to prune so that uninjured canes can be selected for fruiting. Some cultivars are much more prone to winter injury than others, so if time is limited, growers can prune their hardiest cultivars first and the least hardy cultivars last.
Delaying pruning until later in the dormant season also tends to hold back growth that may be affected by untimely frosts. However, pruning should be completed before bud swell since cane removal may cause bud breakage, especially on vines trained with catch wires such as the vertical shoot-positioned system (VSP). Bleeding—flow of sap from the wounds—may occur when vines are pruned late, but this does no harm to the vine.
There are two basic types of pruning—cane pruning and spur pruning. These differ only in the length of the one-year-old fruiting wood that is retained. Cane pruning requires that long, 10- to 20-node fruiting canes be retained for fruiting. Spur pruning utilizes short, 2- to 6-node canes (called spurs) for fruiting.
Most cultivars will perform well using either cane or spur pruning. Some training systems employ both types of pruning. Some cultivars have been reported to perform better when cane pruned because the buds that are four to 12 nodes from the base of the cane are more fruitful than at the basal two or three nodes. Proper shoot positioning should improve fruitfulness of the basal nodes and make spur pruning feasible.
Some cultivars have a tendency to push many secondary and tertiary buds from canes and latent buds from cordons. Short spur (two node) pruning seems to exacerbate this problem whereas long spur (six node) or cane pruning seems to reduce this tendency. Whichever type of pruning is performed, the training system must effectively display the fruiting wood.
Grapevines produce fruit only from one-year-old wood, called a cane; thus, long or short canes should be retained during pruning. These canes are selected based on the following criteria:
Although 60 or more buds can easily be left on a grapevine, a crop of 6 tons per acre cannot be expected unless the vine has sufficient vigor to support such a fruit load. To determine the potential fruit capacity of a vine at pruning time, growers can use the concept of balanced pruning. The principle is valid for all grapes in general, but varies in magnitude from one cultivar to another. The procedures outlined in this section have been developed for Concord. Also discussed are modifications of the principle to apply to other cultivars.
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| FIGURE 26. Balanced pruning consists of weighing the pruned wood from one-year-old canes to determine the number of buds to retain for optimum cropping. |
For best results with Concord, use the (30 + 10) formula. This means that 30 buds are left for the first pound of prunings plus 10 buds for each additional pound of wood removed. If the prunings weigh 1 pound, leave 30 buds; if 2 pounds, leave 30 + 10 = 40 buds; if 2.5 pounds, leave 30 + 10 + 5 = 45 buds; and so on.
Pruning formulas vary depending on the type of grape or cultivar. See Table 8 for suggested pruning formulas for commonly grown cultivars.
For example, if a Concord grapevine has a vine size of 3 pounds, then prune so that 30 + 10 + 10 = 50 buds remain on the vine.
Using a cane-pruned training system (such as the Umbrella Kniffen), the grower would leave five or six canes, each with 10 to 12 good buds, plus some renewal spurs.
Using a spur-pruned training system (such as the bi-lateral cordon), the grower would leave 10 or 12 fruiting spurs, each with 5 or 6 buds plus some renewal spurs.
Leaving 10% to 20% more buds than called for by the balanced pruning formula will adjust for lack of fruitfulness. If winter injury is significant, then adjustment can be made for percentage live (or dead) buds.
Cold injury to grape buds is relatively easy to detect. Using a sharp razor blade, make a series of cross-sectional cuts across the buds, getting deeper with each cut until the primary bud is exposed. Cutting too shallow reveals only the brown bud scales, and cutting too deeply misses the center of the bud and reveals the basal tissue, which may appear alive even if the bud is not. Live buds appear bright green while dead buds appear brown or black.
It is important to thoroughly sample the vineyard and properly handle the canes prior to evaluation of cold damage. Collect canes with 100 or so buds from each cultivar. A sample of ten 10-bud canes is usually sufficient. Samples should be collected after the end of the cold period has occurred, brought indoors, and allowed to warm for 24 to 48 hours to make the damaged buds easier to differentiate from live buds.
Samples should be representative of the type of wood that will be left at pruning in terms of the node position on the canes. For instance, f you normally spur prune to five or six node spurs, then you will want to pay particular attention to damage to the basal five or six buds. Depending on the circumstances, there can be considerable difference in cold damage to buds from the base to the tip of a cane. Keep track of the position of the buds as you cut and record the damage so you will know what part of the cane has the most damage.
For American cultivars in which secondary buds are not very fruitful, the general rule of thumb is as follows:
For instance, if you have 30% bud kill on Concord, you will want to leave 30% more buds than is called for by the 30 + 10 formula. For a vine that produced 2 lbs. of prunings, you would leave 40 + (30% x 40) = 40 + 12 or 52 buds. The extra buds retained should make up for the percent that has been killed and should produce fruit that will help keep the vine in balance.
It is important to determine if there is a relationship between bud kill and node position. If most of the damage is confined to basal buds (because they were shaded and did not acclimate well), then you would want to leave longer spurs rather than more short spurs to account for the total number of buds.
For French hybrid cultivars that have fruitful secondary buds, the increase in number of buds to retain may not be proportional to bud damage. There is no exact formula to determine the number of extra buds to retain, but realize that some adjustment is necessary. It is always best to leave more buds than needed, rather than fewer. Final adjustments can be made by removing shoots after bud break.
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| FIGURE 27. Double pruning delays bud break of basal buds, thus minimizing crop loss from frost injury. A follow-up pruning is necessary to adjust bud count. |
Frost is another possible time of cold injury to buds following budbreak. Pruned vines tend to bud out earlier than unpruned vines. However, delaying pruning until after budbreak is not practical in most cases because cane removal may cause a significant amount of bud breakage. On cold tender cultivars and cultivars that bud out early (such as Marechal Foch), the best approach may be to do a first rough pruning, leaving considerably more buds than required (long spurs), then follow up to adjust bud number after budbreak. This approach, often called double pruning, can sometimes delay budbreak of the desired basal buds by up to two weeks (Figure 27.) It is most practical on spur pruning systems such as high cordon or VSP.
Pruning and cluster thinning: In general, pruning formulas work well for American and vinifera varieties. However, some French hybrids tend to overcrop (very fruitful buds) and using the pruning formula alone to control yield is not adequate. In this case, balanced pruning should be followed by cluster thinning (Table 8). Examples of varieties that require cluster thinning include Chambourcin, Chancellor, Seyval, and Vidal.
| Table 8.Suggested Pruning Formulas for Various Grape Cultivars. | |||
| Grape Cultivar | No. of Buds for 1st Pound of Prunings | No. of Buds for Each Additional Pound | Maximum No. of Buds |
|---|---|---|---|
| American Cultivars: | |||
| Concord | 30 | 10 | 60-70 |
| Catawba | 25 | 10 | 40-50 |
| Delaware | 25 | 10 | 40-50 |
| Niagara | 30 | 10 | 60-70 |
| Norton (GDC) | 60 | 10 | 80-90 |
| French-American Hybrids: | |||
| Foch | 30 | 10 | 60-70 |
| Leon Millot | 30 | 10 | 60-70 |
| Baco Noir | 20 | 10 | 50-60 |
| Vignoles | 15 | 15 | 60-70 |
| Vidal | 15 | 5* | 30-40 |
| Chelois | 10 | 10 | 30-40 |
| Chambourcin | 20 | 20* | 30-40 |
| Chancellor | 20 | 10* | 30-40 |
| DeChaunac | 20 | 5* | 30-40 |
| Seyval | 20 | 10* | 30-40 |
| Villard blanc | 20 | 10 | 30-40 |
| Chardonel | 20 | 20? | 40-50 |
| Traminette | 20 | 20? | 40-50 |
| European (Vinifera) Cultivars: | |||
| 20 | 20* | 40 | |
| Seedless Table Grape Cultivars: | |||
| Canadice | 30 | 10* | 50 |
| Himrod | 30 | 10* | 50 |
| Mars | 30 | 10 | 60-70 |
| Reliance | 30 | 10* | 50 |
| Vanessa | 30 | 10* | 50 |
| * Requires cluster thinning. | |||
| ? Tentative formula. | |||
Pruning and shoot thinning: Under conventional trellising systems, if more than 60 buds should be left on a pruned vine, considerable shading may occur. A general rule of thumb is that six shoots per foot of row are about the maximum that can be left and still achieve good sunlight distribution on the leaves. This varies somewhat with cultivars, but it is a good rule to follow.
This means that vines spaced at 8 feet apart in the row will have the best sunlight distribution with about 50 shoots. Leaving an additional 10 buds can make up for blind nodes. Pre-bloom shoot thinning can be used to make the final adjustment in shoot number.
Assessing vine balance and crop load: Each vine must be pruned according to its own individual capacity. If the crop was large last year, the vine may not have produced enough growth this year to mature a similar amount of fruit. Nutrition and moisture may have been limiting factors. If the yield was low, examine and evaluate the canes of the previous season according to the guidelines given for size, color, and internode length. (See Characteristics of Retained Wood at Pruning.)
Table 9 lists guidelines for growers to assess whether their mature vines are balanced. This balance is gauged by vine size, crop size, and the ratio between the two called crop load.
Vine size is measured by weighing cane pruning per vine (in pounds) during the dormant season. Crop size is the fruit weight per vine (in pounds) measured at harvest. Crop load is the ratio of crop size/vine size.
Optimum crop load ranges between 5 (for low-yielding vinifera) and 12 pounds of fruit or higher (for high-yielding vinifera and hybrids). This means that for every pound of prunings produced, 5 to 12 pounds of good-quality fruit can be produced by the same vine. For example, if a grapevine has a vine size of 2.5 lb. (pruning weight), then in order to achieve a balanced vine, the optimum crop size for this vine should range between 5 x 2.5 = 12.5 lbs. and 12 x 2.5 = 30 lbs. of fruit.
| Table 9. Assessing Grapevine Balance Based on Vine Size, Crop Size, and Crop Load. | |||
| Class of Vine Size | Vine Size (Lbs/ft of Canopy) | Vine Size (lbs/vine) On 8-Ft Vine Spacing | Crop Load (Crop Size / Vine Size) |
|---|---|---|---|
| Small | Less than 0.25 | Less than 2 | More than 15 |
| Comments and Recommendations: “Overcropped” vines. Vines produce too much fruit and not enough shoots. Should reduce crop by cluster thinning and fertilize to restore vine size. | |||
| Medium | 0.3 – 0.4 | 2.4 – 3.2 | 5 - 12 |
| Comments and Recommendations: “Balanced” vines. This situation is optimum. Should keep the same vineyard practices. | |||
| Large | More than 0.4 | More than 3.2 | Less than 3 |
| Comments and Recommendations: “Vigorous” vines. Vines produce too many shoots and not enough fruit. Reduce or withhold fertilization; practice canopy management; may convert to a divided training system if none of the short-term remedies work. | |||
After the vine or vineyard section has been pruned, the prunings are placed between the rows. Prunings should be removed carefully from the trellis to avoid breaking those canes retained for production. The prunings may be removed from the vineyard or chopped between the rows with a heavy-duty rotary mower or flail mower. Most commercial vineyards chop the prunings, which reduces labor for this operation while adding a small amount of organic matter to the soil.
Training is the arrangement of the vine on the trellis. There are many different types of training systems for wine grapes, but all have the same goals:
Optimum sunlight exposure of leaves and fruit ensures good fruit quality and bud fruitfulness. Without adequate exposure, fruit quality suffers and vine productivity is reduced.
The most efficient training systems provide well-spaced, evenly distributed fruiting wood along the trellis to promote maximum interception of sunlight and provide optimum sun exposure for clusters and shoots. In addition, a well-designed training system will produce a high canopy surface area and low canopy density. This encourages high production of sugars with minimal effects of shading.
Researcher and grower experiences have shown that shoot density of about six shoots per foot of canopy is optimal. This should provide a canopy that has one to two layers of leaves and minimal shading. As shoot density gets higher, leaf layers increase and shading occurs.
Shading has detrimental effects on fruit quality, such as lower soluble solids; higher total acidity; higher pH; reduced color, anthocyanin, and phenolic content; and increased potassium content. Wine quality can be adversely affected by each of these changes. Understanding that sunlight exposure is necessary for good fruit quality is the basis of training and trellising system selection.
Growers are advised and cautioned that there is no universal training system. One-size-fits-all does not apply in choosing a training system. With this in mind, a grower should realize that choosing a training system depends on several factors, including the anticipated vigor of the vineyard, cultivar to be planted, capital and annual labor cost, equipment used, and the potential to mechanize the vineyard.
Trellis construction is one of the most expensive components of vineyard establishment. It makes sense to carefully consider the reasons for choosing a particular training system.
Anticipated or potential site vigor is probably one of the most important factors in selecting a training system, but it is difficult to assess. The selection of a training system and vine spacing should be based on the anticipated vigor of the vineyard.
In the Midwest, many vineyards are being established for the first time, thus predicting vine vigor prior to vineyard establishment is challenging. Table 10 provides guidelines for selecting the proper training system and vine density based on vine vigor and potential site vigor.
Vine vigor is affected by rain, soil type, depth, fertility, water-holding capacity, and cultivar. Thus, information on these factors should be gathered to assess the anticipated vigor of the site as accurately as possible. New growers should check neighboring vineyards to have a general idea about vigor potential in their area.
Eventually, growers should be able to rank their new vineyard sites as low, moderate, or high vigor. In general, in a low-vigor site, choosing a non-divided canopy training system (e.g., VSP) is the most adequate, whereas in a high-vigor site, choosing among divided canopy training systems (e.g., GDC) is recommended (Table 10).
| Table 10. Guidelines to Matching Training Systems with Potential Vineyard Vigor Based on Anticipated Site Vigor, Variety Vigor, and Row and Vine Spacing.1 | ||||||||||
| Training System Selection | Anticipated Site Vigor2 | Scion and Rootstock Vigor2 | Row Spacing Selection3 | Vine Spacing Selection4 | ||||||
|---|---|---|---|---|---|---|---|---|---|---|
| High | Moderate | Low | High | Moderate | Low | Narrow | Wide | Narrow | Wide | |
| Non-Divided Canopy | ||||||||||
| Vertical Shoot Position | - | + | ++ | - | + | ++ | ++ | - | ++ | - |
| High Cordon | + | ++ | - | + | ++ | - | ++ | + | + | ++ |
| Divided Canopy | ||||||||||
| Smart Dyson | ++ | ++ | - | ++ | ++ | - | ++ | - | ++ | + |
| Scott Henry | ++ | ++ | - | ++ | ++ | - | ++ | - | ++ | + |
| Geneva Double Curtain | ++ | + | - | ++ | + | - | - | ++ | + | ++ |
| Lyre or “U” | ++ | + | - | ++ | ++ | - | - | ++ | + | ++ |
| 1 Anticipated Site Vigor Ranking: High = deep and fertile soil, abundant water availability, and high water-holding capacity; Moderate = moderately deep and fertile soil, moderate water availability, and moderate water-holding capacity; Low = shallow and low fertility soil, scarce water availability, and low water-holding capacity. | ||||||||||
| 2 ++ Most appropriate match; + Appropriate match; - Least appropriate match (not recommended). | ||||||||||
| 3 Row spacing: Narrow = 8 to 10 ft; Wide = 11 to 12 ft. | ||||||||||
| 4 Vine spacing: Narrow = 4 to 6 ft; Wide = 7 to 10 ft. | ||||||||||
The choice of the training system must take into consideration cultivar and rootstock vigor, growth habit, cold hardiness, and disease susceptibility. The choice of the training system is often dependent on the growth habit of the cultivar being grown.
Most American and French hybrid cultivars tend to have a downward, or procumbent, growth habit. Therefore, a high training system, which allows ample distance for shoots to grow downward, is recommended. On the other hand, European, or vinifera cultivars, have a strong upright growth habit, especially early in the growing season. This growth habit is best managed with a low training system, which allows upward vertical shoot growth.
To date, there are more than a dozen training systems used throughout the world. In the Midwest, training systems used for wine production range from single to divided curtain systems with the High Cordon system being the most common. Although the High Cordon system is commonly used, it is not always the most adequate. A general description of each system and its pros and cons is presented here.
The HC or single curtain is the most commonly used training system in the Midwest. Two cordons extend along the top wire (5.5 to 6 feet above ground) of the trellis in each direction and meet cordons half way from adjacent vines. The cordons remain as semi-permanent extensions of the trunk, though they may need replacement every five or so years.
A second training wire may be used at 36" to 42" above ground to provide extra support for young and mature vines and minimize breakage from strong winds. This system can be cane- or spur-pruned; however, the latter is more common. Fruiting spurs two- to six-nodes long are spaced along this cordon. Shorter renewal spurs are left to provide fruiting wood for the next season.
The primary advantages of HC are low establishment and production costs and ease of mechanization, including mechanical harvesting and pre-pruning. The high location of the fruit and renewal zones improves sunlight penetration, which thus has the potential to increase yield. Wildlife depredation (deer) and frost injury may also be minimized.
This system is best suited for use under moderate vigor conditions, which are the conditions most common in the Midwest. Most of the Hybrids and American cultivars with procumbent growth habits are adapted to this system.
Umbrella Kniffin (UK) used to be the most popular and common system in the Midwest and the East. This system utilizes long canes (10 to 20 buds each) that originate from renewal spurs at or near the top of the trunk. Four to six canes are retained, bent over the trellis wires, and tied securely.
Mechanical damage to the tender buds during the tying process can be a problem, so pruning and tying must be finished before bud swell begins. Other drawbacks of this system include extra time and effort for tying, and difficulty in leaving extra buds to protect against damage from spring frosts (double pruning). Additionally, cane pruning cannot be mechanized. In recent years, UK has been used less in newly established vineyards.
This Vertical-Shoot Position (VSP) system is also called low- or mid-cordon system and is the most commonly used trellis worldwide on vinifera cultivars. Trunks are trained to a low (12") or mid wire (up to 42") with cordons or canes extending along this wire. Shoots are positioned vertically upward between two to three pairs of catch wires.
The first pair of catch wires is positioned about 10" above the cordon wire; the second and third at 12" and 24" above the first catch wires. Shoot positioning is done by either moving catch wires or by manually tucking shoots between fixed catch wires.
The advantage of this system is that the distance between rows can be reduced, allowing more efficient vineyard design and improved productivity. It is also easy to manage and mechanize. This system keeps the fruiting wood close to the ground to allow easy renewal of trunks in case of winter injury.
The disadvantages of VSP are lower light exposure than HC since the fruiting zone is at the base of the canopy; thus, lower yields than HC are expected. Furthermore, the proximity of the fruit zone to the ground makes it more susceptible to wildlife depredation and frost injury.
VSP is normally used under low- to moderate-vigor conditions. This system is most suited to cultivars with upright growth habit, including most vinifera cultivars and some hybrids (e.g., Chancellor, Seyval, and Vignoles).
The Fan System (FS) is often used with cold tender cultivars to assure some live buds each year. This is a spare-parts approach in which several trunks of different ages are retained and spread out across a multiple wire trellis. Older trunks are often more susceptible to winter injury than young trunks but are also more fruitful, so trunks of different ages are saved to provide for continuous renewal of fruiting wood.
Fruiting wood is selected from canes on the different trunks. In case of winter injury to one trunk, additional buds are retained on the remaining trunks to balance the bud number. Fruiting wood may be pruned as long canes or short, depending on the degree of winter injury and available buds.
As the name indicates, Geneva Double Curtain (GDC) was developed at the New York Agriculture Experiment Station in Geneva, New York, by the late Dr. Shaulis. This system is similar to HC but instead of having a single curtain of shoots, there are two horizontally divided curtains. These curtains are supported by fruiting wires that are separated by cross arms that are usually 4-feet wide.
Since the two curtains extend 2 feet on each side beyond the vine row, row spacing should be wider than other systems. Row spacing of 11 to 12 ft is generally recommended. Vines can be trained either with two cordons (bilateral) on one side of the canopy, or four cordons (quadrilateral), with two on each side of the canopy. At the same vine spacing, the bilateral cordons are twice as long as the quadrilateral cordons.
Field observations indicate that GDC with quadrilateral cordons produces more uniform bud break and shoot growth; cordons have less blind nodes and are quicker to replace in case of disease or winter injury than GDC with bilateral cordons.
The GDC system supports more growth and yields (30% or more, higher than HC) since shoot number and leaf surface areas are doubled (Table 11). Thus, GDC is more suitable under high-vigor conditions where soils are deep and fertile. This system is also suitable to vigorous cultivars such as Concord, Frontenac, Norton, and Traminette and some table grapes.
GDC produces higher fruit quality, higher yields, and less disease incidence than other systems. Although GDC has a high establishment cost due to more trellising materials, the long-term benefits from higher revenues exceed the initial costs. A potential drawback of GDC under a hot climate is excessive fruit exposure to sunlight and heat, which may result in sunburn and may negatively affect flavor components, especially of white varieties.
| Table 11. Exposed Canopy Surface Area for Different Training Systems (Smart, 1996). | |
| Trellis System | Surface Area for 12-ft. Row Spacing (m2/ha) |
|---|---|
| VSP | 8,500 |
| HC | 12,500 |
| SH | 13,100 |
| SD | 13,100 |
| SD – Ballerina | 13,700 |
| GDC | 20,000 |
The Scott Henry (SH) system is similar to VSP, but curtains are vertically divided upward and downward. Vertical curtains are formed by alternating the fruiting zone height. Shoots from the upper canes (or cordons) are positioned vertically upward, while shoots from the lower canes (or cordons) are positioned downward, leaving an open space or window 8" to 10" wide between the two curtains.
SH is best adapted for moderate to high-vigor conditions. The SH trellis system uses 8 wires—two cordon wires, two pairs of catch wires for the upper curtain, and one pair for the lower curtain. Therefore, SH is more labor intensive than the previous trellising systems.
Advantages include higher yields and quality than VSP. Thus, the high establishment and production costs may prove to be worthwhile in the long-term. Another significant advantage of SH is reduction in bunch rot, which causes yearly crop losses for several cultivars grown under wet and humid conditions. Cultivars prone to bunch rot, such as Pinots and Vignoles, can benefit from this system.
Originally, Oregon grower Scott Henry developed this system to overcome two problems in his Pinot noir vineyard—excessive vigor and bunch rot. The SH system has promise, but there is limited commercial experience in the Midwest, and more research is needed for long-term evaluation of this system.
This Smart-Dyson (SD) system is similar to SH where curtains are vertically divided. Thus, SD has similar advantages to SH. The only difference with SH is that shoots in SD originate from the same cordon or fruiting zone. Also, SD requires one type of pruning called spur pruning, which is easier and less labor intensive than SH. This system is adaptable to machine harvesting, pre-pruning, and leaf removal. Smart-Dyson Ballerina is a modification of the SD system, with very similar training except that the Ballerina is used more often in cases of retrofitting existing vineyards from VSP in case of excessive vigor.
As with SH, there is limited experience and research with SD, and further evaluation of this system is needed.
The Lyre or U-System (U) is similar to VSP but with two curtains divided horizontally. Thus, this system is adapted to upright growing cultivars and is suitable to moderate and high-vigor conditions. As with other divided canopy systems, yields are increased due to increased shoot number and leaf area per acre.
However, the U system is the most expensive to build among all training systems. Furthermore, this system is difficult to mechanize. Because of the extensive cordon development required, this system is difficult to maintain in areas where cold injury is common. Therefore, this system is generally not recommended in the Midwest.
Another trend that has developed in recent years is the use of mechanical pruning, or minimal pruning, techniques. Much work has been done in New York and Arkansas to mechanize all aspects of grape production.
Training systems employed are usually High Bilateral Cordon or Geneva Double Curtain. Pruning severity can range from closely approximating hand pruning to only minimal skirting of canes in the lower section of the trellis. These systems are probably best suited for juice grapes, but wine grapes are increasingly being grown using these systems.
More research is needed to evaluate minimal pruning under high disease pressure and extreme low temperature conditions characteristic of the Midwest.