Table Grapes: A Potential Alternative Crop
Larry A. Stein and George Ray McEachern
Texas Cooperative Extension
Table grapes typically require a hot, dry climate, deep well-drained soil and a large amount of irrigation water. As such, California, southern Arizona and northern Mexico have dominated the springtime commercial table grape market in the United States for many years, while Chile has traditionally supplied the fall market.
In Texas, there is an opportunity for small, local table grape production west of the 30-inch annual rainfall line. Tests of fungicide programs and new grape varieties from New York, Arkansas and Florida as well as from California have recently been conducted in Texas.Initial table grape trials by the TAMU Research and Extension Center at Stephenville and by Extension cooperators throughout the state have demonstrated that table grapes can be effectively grown in Texas. However, further testing is needed to determine commercial feasibility. In Stephenville, 51 varieties have been evaluated with a wide range of growth responses. Some 16 additional varieties are being evaluated at cooperator sites across the state.
The major limiting factors for commercial table grape production are:
- Pierce’s Disease (PD) and cotton root rot.
- Freezing (fall, winter and spring)
- Black rot disease from high humidity
- Varieties with adequate quality
- Technical management requirements
Because of their high quality requirements at the point of sale, table grapes demand hand labor, technical knowledge and experience. All initial plantings should be very small until the optimum production system and many specific details are worked out. Marketing, financing, labor and knowledge will be very important factors in determining vineyard size. No grapes should be planted without a detailed production and marketing plan, and a total management plan should always proceed planting.
Table grapes can be successfully grown in some climates and not in others. In Texas, disease and temperature are the two controlling factors and are interrelated with one another.
Disease control is critical for table grape production. Dry climates help reduce the occurrence of black rot, downy mildew and bunch rot problems. Potential growers must not assume fungicides will always control black rot. When rainfall, humidity and temperatures are high from April through July, unmanageable black rot pressure can result. Because of this, a very dry climate is preferred. It is no accident that deserts are the leading areas for commercial table grape production. In Texas, growing table grapes will be difficult in areas receiving more than 15 inches of rainfall during the production season from April to July.
Cold injury from early fall freezes, mid-winter freezes and spring frosts can injure the vines. In Texas, there is less chance of vine injury from freezing the further south a vineyard is established. Since grapes do not have a true rest period, it can be difficult for vines to harden off in the fall. Young vines are especially sensitive to mid-winter freezes. Temperatures below 0oF can kill mature vines; therefore, the average minimum 0oF line is the upper limit for commercial table grape trials in Texas. Spring frosts as late as April can kill new shoots and clusters, reducing the crop to secondary buds.
Heat is important for stimulating early season growth and early ripening. The hotter the climate, the earlier the harvest and the higher the price. Some people believe that southernmost Texas has the potential to produce the earliest table grapes in the United States.
Deep, fertile, well-drained soil is needed for vigorous vine growth. The soil must drain well to insure optimum water and mineral absorption. A wide range of soil pH can be planted; however, it is necessary to add lime to acidic soils. Problems with cotton root rot and iron absorption will occur with very high pH soils. Heavy clay soils which are poorly drained and soils or irrigation water high in sodium must be avoided. Sodium content is reported as the Sodium Absorption Ratio (SAR) and needs to be less than 6.0 for grape production.
Table grape vines must be vigorous to insure high yields and quality; the better the soil, the healthier the vines and the greater the chance for tonnage and quality. County Soil Conservation Survey maps should be studied prior to land purchase to learn about soil characteristics of any potential site.
A commercial table grape vineyard should be located on sites with good accessibility, well drained soil, clean irrigation water, no frost pockets, few predators, electricity, and other factors which affect marketing.
For maximum vine growth and vigor, vines should be spaced 8 feet apart, and rows should be placed 12 feet apart. Vines planted closer than this are too shaded and may have to compete for water and nutrients, thereby reducing grape production and quality. Proper spacing also allows for good air movement which is essential for the reduction of potential black rot problems.
Healthy, 1-year old rootings should be used for planting. Vines should be planted on a rootstock only if the vineyard site dictates. Vines should be ordered from a reputable nursery well in advance of the planting date. Set the vines in January or February. Trim all roots to 3 inches. Prune all canes except the most vigorous, always leaving two buds. A hole only as large as the root system is required to plant the vine. Pack the soil tightly around the vine and water immediately with three gallons of water.
Only large, number-one, rooted vines should be planted. Weaker vines will not develop sufficient roots the first year to insure good vine training the second year. From the second to the fourth year, follow the procedures outlined in the Texas Vineyard Guide, B-1424.
Pruning and Canopy Management
Proper pruning results in vines with good vigor, large clusters and large berries. If the vines are too vegetative, the crop will be short and fruit quality will be low due to shading year after year. On the other hand, if over-cropping is allowed to occur, the fruit will be low quality, harvest will be late, and in extreme cases, the vine can die. Unfortunately, there is no simple rule for pruning table grapes; each vine needs to be pruned to maintain the delicate balance between vine vigor and fruit production. This is not easy and is often misunderstood even by professional horticulturists and commercial grape growers. Factors to consider in controlling vine vigor include: climate, soil, variety, rootstock, irrigation, weed control, trellis, cluster thinning and other forms of management.
Sunlight is also a major consideration for the table grape grower because it controls fruit quality and fruit bud initiation for next year’s crop. Light must contact the developing buds in the leaf axils on the lower end of a shoot during May and June each year. This sunlight is essential for the initiation of fruit buds for next year’s crop. If lower buds on this year’s shoot are shaded by more than three leaf layers, next year’s crop will be low with fewer clusters and fewer berries in each cluster. Therefore, the grape grower needs to manage vine vigor so that sunlight can adequately reach developing buds. Fruit thinning by hand is necessary to produce large cluster and berries.
Optimum vigor shoots will be 3/8 to 1/2 inch in diameter and contain 15 to 22 healthy leaves in July when the fruit are developing and ripening. Every vine must be managed by pruning to the correct number of buds so that the shoots will have the vigor and sunlight. Vines which make excess growth one year will need to be pruned to leave more buds the following year. Vines which are weak need to be pruned harder, leaving fewer buds to increase vigor. Each vine should be evaluated every year to determine the proper number of buds to leave on the vine after pruning.
The Cane Count rule can be used to estimate the proper number of buds to leave after pruning. Using the Cane Count rule, if a vine produces 40 healthy canes measuring 3/8 inch in diameter, leave a bud for every cane minus 10 percent, leaving a total of 36 buds on the vine after pruning. Using this rule, the table grape grower can determine the exact number of buds to leave on the vine after pruning. If pruning is ignored, and the vine is allowed to grow unmanaged, excess vigor, poor quality, over-cropping, late harvest, and potential vine death will result.
Numerous systems are used around the world to obtain the proper balance between grapevine vigor and fruiting. Table grapes are pruned to the Bilateral Cordon or the Double-T Cane system.
Cane. The Double-T cane pruning system is useful when growing table grapes because of the balance achieved between fruit and vegetation and because of bud count flexibility. Sun canes from renewal spur buds are both vigorous and fruitful from year to year. Vines can be pruned to 8 or 24 buds with only 2 canes, or to 16 or 32 buds on a 4 cane system. Since new canes are selected each year, long term loss from hail or freeze is reduced. If excess vigor is a problem, more buds are left on the vine. The total bud count per vine can be used to dramatically increase cluster and berry size. Large cluster varieties can be pruned to fewer buds per cane on mature vines, producing fruit far superior to that obtained on a bilateral cordon vine. All varieties can be cane pruned.
Bilateral Cordon. The Bilateral Cordon is the most common pruning system currently in use for wine grapes in Texas, and it will also work for table grapes. Vine vigor and production are well-balanced with 28 to 32 total buds on 14 spurs. The bilateral cordon is very difficult to train during the second and third years of vineyard establishment, but is extremely easy to prune thereafter. Hail and freeze damage to the horizontal cordons has caused some growers to shift to a cane system with temporary canes rather than permanent cordons.
The Bilateral Cordon system is well-designed for leaf pruning and for exact fungicide placement to control black rot and bunch rot. All varieties except Thompson Seedless can produce good crops using the bilateral cordon if over-cropping or excess vigor is not a problem.
Table grapes need to be vigorous with the canopy positioned for maximum sunlight absorption. A Double-T Lyre trellis is best. The Double-T trellis should have 12-gauge wires spaced at 18 inches for the drip irrigation line, 42 inches for the main wire, two cane wires at 52 inches spaced 12 to 18 inches apart, and top wires at 66 inches spaced 24 to 36 inches apart (Figures 1, 2 and 3).
In situations where climate, soil and site may potentially reduce vine vigor, the Bilateral Cordon can be used. The cordon trellis has vertical wires at 18, 42, 52, and 66 inches (Figure 4).
In Texas, standard metal fence posts with welded cross arms are used as stakes at each vine. End posts should be at least 6 inches in diameter, should be sunk to a depth of 36 inches in the ground, and should be pressure treated. Intermediate posts should be 4 inches in diameter, sunk to 24 inches in the ground, and spaced at every 10 vines down the row.
Selecting the proper variety is critical to the success of a table grape vineyard. Current recommendations are based on data gathered over the last three to five years; hence, growers are urged to plant limited numbers. Table grapes need to be large and thin-skinned with true seedless berries, and need good flavor as well as consumer appeal and acceptance. Such restraints drastically reduce the number of varieties for planting. To date, California varieties have the best quality and consumers are familiar with them.
If you do not object to seeds, there are a number of good seeded grape varieties which can be grown in Texas. Consumer acceptance of seeded varieties has been low even though the quality can be excellent. Current variety recommendations are provided in Table 1. Other varieties can be grown, but you must be aware that each variety has specific cultural requirements in order to produce quality fruit. Essentially, growers have to learn how to grow a specific variety. For example, there have been problems with the Venus variety. Even though it is a beautiful grape and cluster, it has a tough skin, palatable seed remnant, must be pruned hard and be totally ripe before harvest.
- Blush seedless produces sizable clusters of large red berries with little cluster manipulation. The vine is somewhat cold tolerant.
- Flame seedless has set the standards for table grape quality around the world. It is a vigorous vine which is somewhat sensitive to cold winter temperatures. Clusters require gibberellic acid (GA) to attain adequate berry size.
- Thompson seedless is a very vigorous vine on fertile soil and produces long clusters of small berries without GA applications. The vine is sensitive to cold and should be cane pruned and heavily cluster thinned for best production.
- Reliance is a very sweet, small-clustered pink variety with small berries. Production and cold tolerance are excellent, but quality is subjective and atypical.
- Glenora is a small-clustered New York grape with excellent cold tolerance. Berries are small but have excellent flavor.
- Autumn seedless is a late-ripening white grape with large berries and medium sized clusters. It is somewhat sensitive to cold.
- Himrod is a very productive white grape with excellent cold and some frost tolerance. Clusters are typically loose and berry quality is fair to good.
- Romulus is a white grape with good quality and good cold tolerance.
- Vanessa has outstanding quality and a crisp, fruity flavor. Production and cold tolerance are good.
- Centennial seedless produces medium clusters of large, white, oval-shaped berries. Production is fair as the vine is somewhat sensitive to cold.
- Orlando seedless is a long-clustered, light green, white berry variety with Pierce’s disease resistance. It is a vigorous vine with some cold tolerance.
It is not uncommon for vigorous plants to produce fruit clusters the first year. To insure healthy vine development, pinch off all clusters as they appear during the first and second years. Avoid over-cropping during the third and fourth years to prevent weakened vines and uneven spur development. Pinch off all but one cluster per shoot during the third and fourth years. Small, misshapen shoots and clusters should always be removed. Mature vines should be limited to only 16 to 20 clusters per vine. Remove extra clusters by hand immediately after fruit set.
Table 1. Table grapes worthy of trial planting.
|Blush Seedless||fair||good||large||no||spur or cane||red||no||good|
|Flame Seedless||fair||fair||small||yes||spur or cane||red||no||excellent|
|Reliance||good||good||small||no||spur or cane||pink||no||good|
|Glenora||good||good||small||no||spur or cane||purple||no||excellent|
|Autumn Seedless||fair||fair||large||no||spur or cane||white||no||good|
|Himrod||good||good||medium||no||spur or cane||white||no||fair|
|Romulus||good||good||medium||no||spur or cane||white||no||good|
|Vanessa||good||good||medium||no||spur or cane||red||no||good|
|Centennial Seedless||fair||fair||large||no||spur or cane||white||no||good|
|Orlando Seedless||good||good||small||no||spur or cane||white||yes||fair|
A number of cultural practices can be used collectively to increase the size of table grape berries. It is essential to have a very vigorous vine produced by heavy pruning. There should never be more than one cluster per shoot. A mature vine should be cluster thinned to only 16 to 20 clusters per vine. If the vine is not vigorous, the number of clusters should be drastically reduced. Other clusters should be pinched off immediately after berry set. All but the largest and best-shaped clusters should be removed.
Many table grape varieties such as Thompson Seedless, Orlando Seedless, and others have long clusters which should be pruned in half at the same time as cluster thinning. This cluster pruning will reduce the number of berries per cluster by 50 percent and greatly increase the size of the remaining berries.
Girdling the trunk by removing a 1/4 inch band of bark 20 inches above the ground one week after berry set can also increase berry size. Girdling should only be practiced on extremely healthy vines over four years old which have a trunk at least 3 inches in diameter.
Berry size can be significantly increased by heavy pruning, cluster thinning, cluster pruning and girdling. However, Thompson seedless and Flame seedless berries can also be enlarged by applications of gibberellic acid (GA). The first GA spray should be made at full bloom to reduce berry set. Two subsequent applications are made to greatly increase berry size. The second application is made when the berries are about pea-sized, and the third application is made two weeks later. The first GA spray is at a rate of 4 to 6 ppm, while the second and third are at 20 to 30 ppm. All berries in the cluster need to be covered with the GA spray for best results. All other varieties are extremely sensitive to GA, and its use will damage the current crop and next year’s crop as well.
Weeds are fierce competitors for water and nutrients and must be controlled to allow optimum vine growth and to reduce the buildup of insects and diseases in the vineyard. A combination herbicide and mowing system is best for table grapes. A closely-mowed strip of sod between rows provides space for sprayer traffic during periods of wet weather to prevent black rot development. Herbicides are used under the vines to prevent weed growth. Combinations of post- and pre-emergent products are needed to keep grass and weeds out of the vineyard. Weed control is more critical when soils are shallow or irrigation is limited.
Since large berries are essential in the table grape market, irrigation is critical. Grapes require 1 inch of water per acre per week. Depending on soil type, table grapes should never go longer than two weeks without irrigation. Drip irrigation is an excellent method; use one emitter per vine placed 12 to 18 inches from the trunk. Very sandy soils may require two emitters per vine. Table 2 provides a general guide for the amount of water to be applied. Water should be kept in the upper 3 feet of the root zone and irrigation should never be turned off until after harvest. Intentionally stressing the vines is detrimental to table grapes.
Table 2. Gallons of water required per vine per week.
|*Water only if extremely dry.|
Table grapes are adapted to a wide range of soil types and usually require less fertilizer than other crops. Most growers need only be concerned with nitrogen requirements. However, other nutritional problems such as iron or zinc deficiencies may occur in Texas. Maintaining proper vine growth is based on past experience, observation and judgment. Observations can be verified with periodic laboratory tissue analyses. Although it is difficult to make specific recommendations, the following are general guidelines. Never fertilize grapes after June because this may stimulate late season growth and freeze injury. Never use phosphorus fertilizer as it can trap iron and zinc in the soil. Grapes grown on heavy, poorly-drained soils frequently have yellow leaves with green veins and an iron deficiency. Improving soil drainage and iron chelate can correct these problems. Foliar zinc sprays may be necessary for light, sandy soils.
Foliar diseases must be controlled to produce high-quality, blemish-free table grapes. The more rain and humidity an area receives, the greater the need for fungicide sprays.
Black rot is the most serious foliar disease. It must be controlled with good vine pruning, shoot positioning, leaf removal, and regular fungicide sprays when the new shoots are 8 to 10 inches long. Several fungicides should be use in rotation to prevent resistance to various fungal diseases. Other diseases which can affect table grapes are downy mildew, bunch rot, anthracnose and dead arm. A good black rot control program will usually keep these diseases in check.
Generally speaking, insects have not been a major problem for table grapes in Texas. To date, the apple twig borer and the grape berry moth have caused the most problems. Problems have also occurred with leaf feeders, aphids and leaf folders, but to a lesser extent.
Birds and other predators can be a serious problem at harvest time. Netting is the best way to prevent fruit loss. Table grapes are harvested when they taste good. Sugar content varies from variety to variety. Many varieties are harvested when the sugar level is above 16 percent, while others require over 20 percent for top quality. Further testing will dictate specific harvest levels in the future. Color development has not been a problem to date on table grapes in Texas.
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