Fruit and Nut Review
"Bunch grape" refers to grapevines having berries borne within a cluster. The entire cluster, or bunch, is harvested as a uniformly ripe, intact unit.
The South does not have the ideal climate for bunch grapes. By carefully choosing the varieties and following the procedures for producing bunch grapes in the South, you can successfully grow bunch grapes.
The worst threat to successfully growing bunch grapes in Mississippi is Pierce's disease, which shortens the life or kills the plants. Muscadine grapes have a natural resistance to Pierce's disease. Some bunch grape varieties have resistance to this disease.
The choice of varieties is important and complicated. The varieties listed below are best for growing in Mississippi, and are resistant to Pierce's disease.
Soil and Climate
Bunch grapes grow best in deep, well-drained, sandy loam soils. Shallow, heavy clay soils will not produce the vine vigor, tonnage, or fruit quality of better drained soils. In general, bunch grapes require a long growing season, relatively high summer temperatures, low atmospheric humidity, a ripening season free from rain, and mild winter temperatures.
Planting and First Year's Growth
Plant the vines in January or February, 8 feet apart in rows spaced 12 feet apart. Set the vines the same depth they grew in the nursery. If vines are grafted, the graft union should be 2 inches above the final soil level. Spread the roots in all directions in the planting hole.
After planting, cut back the vine to leave two or three buds. Place 2-inch by 2-inch posts at each plant to train and support the vine. When the new shoots begin to grow, select the most vigorous and tie it loosely to a stake. Remove all the other shoots.
During the second growing season, train the vines on the trellis. Use No. 10 or No. 12 smooth galvanized wire for the trellis wire. The two horizontal wires on the trellis should be 42 and 72 inches above the ground. Large support posts are needed every 12 vines down the row. The ends of the trellis must be well anchored.
If the vine (trunk) is long enough, loosely secure it to the top wire and cut it off about 2 inches above the wire. If lower canes are present, secure a cane on the lower wire on each side of the vertical main stem. Tip-cut these canes to 8 to 12 buds in length, depending on plant vigor. Allow one cluster of fruit from each bud. Remove all others in early May. Tie a cane to the upper wire on each side of the trunk.
Pruning Mature Vines
Prune according to the vigor of the vine and its production potential. You should do this in the dormant season. Remove canes that bore fruit the previous year. Select four canes that grew the previous year to train to the trellis wires--one cane on each side of the trunk on the upper and lower wires. For strong plants, count 10 to 12 buds on each cane and cut off the rest (eight buds for weak plants).
Select two additional canes close to the top wire and two additional canes close to the bottom wire. Make renewal spurs from these canes by cutting them back to two buds in length. Renewal spurs are canes that will produce fruit the following year. Remove all other canes close to the trunk.
The properly pruned grapevine will have a trunk, four canes for fruit production (10 to 12 buds), and four renewal spurs (2 buds). Proper pruning may remove 90 percent of the wood.
Fertilizer is not a serious limiting factor in young vines. Apply 1/2 pound of complete fertilizer (such as 13-13-13) per vine, split into two equal applications 6 weeks apart. Make the first application in February.
Drip irrigation is excellent for grape culture. Apply 1 gallon of water a day per vine per year of age until you are applying 5 gallons of water per day. Grapes are preconditioned to cold by slowing growth in August. This can be accomplished by cutting off the drip system in early August.
Grape harvest usually begins in mid-July and continues through September. Mature bunch grape vines can produce as much as 25 pounds per year.
Color is a poor indicator of maturity in bunch grapes. Many varieties change color long before they are fully ripe and become sweeter and less acid as they mature. Maturity is usually determined by taste or by the color of the seeds, as they change from green to brown.
If vines are allowed to overproduce, the sugar content of the fruit will be low, the color will be poor, and the maturity of both fruit and wood will be delayed. Immature wood is susceptible to freeze damage, and the next year's crop may be reduced. In the case of severe overcropping, the entire vine may be winter-killed.
By John Braswell, Extension Horticulture Specialist
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