Bunch Grape

Two primary species of bunch grapes are commercially grown in the United States: the European bunch grape (Vitis vinifera) and the American bunch grape (V. labrusca). South Carolina’s climate is not well-suited to home garden production of European bunch grapes, but some American bunch grapes and hybrids between the two species grow well in South Carolina. If they are well-cared for and sprayed when diseases and insects threaten, you can expect yields of 20 to 30 pounds of fruit per vine.

Cultivation

Soil and Site: In the South Carolina mountains and Piedmont, a late spring frost can reduce yields significantly, so plant bunch grapes on elevated sites. In all areas, avoid low spots where cold air settles. The site should be in full sun most or all of the day. Well-drained loam or clay loam soils are best. Bunch grapes also grow well on heavier clay soils; however, excessive vine growth and delayed maturity may result. Avoid areas where water stands after heavy rains.

Trellis Systems: The grapevine does not have a rigid trunk; therefore, some support structure, usually a trellis, must be provided. The trellis design should maximize light penetration inside the canopy, exposing the buds, leaves and fruit clusters, especially in the latter part of the growing season, to as much sunlight as possible. Selecting the right trellis system depends primarily on the type of grape. Although several trellis systems are available, there is no single system that is appropriate for all bunch grapes in all situations.

South Carolina gardeners should consider low- and high-trellis cordon systems. The low-trellis cordon system establishes the cordons 3 to 3½ feet above the ground and includes two to three catch wires positioned at 10-inch intervals above the cordon wire. This system

promotes vertical growth, resulting in a narrow, upright vertical canopy that speeds up the drying of leaves and fruit, which helps to reduce disease outbreaks. French hybrid and Vitis vinifera grape cultivars should be trained to a low-trellis cordon.

The high-trellis cordon system establishes the cordons 5 to 6½ feet above the ground. Grape cultivars suited to the high trellis are very vigorous and have a trailing growth habit. For American (“non-labrusca”) and American hybrid grapes, establish the cordons at the lower limit of the high-trellis cordon system, about 5 feet above the ground.

Trellis Construction: To simplify installation and to avoid damaging the young vines, build and erect the trellis system before the vines are planted. Construct the trellis with pressure-treated wood to resist decay or a durable type of wood such as cedar or locust. Use 11 to 12.5 gauge high-tensile galvanized steel wire and wire strainers to maintain wire tension. Space vines 8 feet apart in the row and space rows 10 feet apart. Plant the first and last vine 4 feet in from the end posts, and set line posts at 20- to 30- foot intervals down the row (about three vines between line posts).

Purchasing Plants: Bunch and French hybrid grapes, unlike muscadines, do not require cross-pollination. Therefore, it is not necessary to buy two or more cultivars for pollination. However, several cultivars can extend the harvest season.

Variety Selection: Many varieties of bunch grapes will perform well in the mountains and Piedmont. Also, certain selections of French hybrid grapes (wine grapes) are suggested for trial in these areas. Several new hybrid bunch grapes are worthy of trial in the sandhills and coastal plain. All of these have good resistance to Pierce’s Disease, the primary limiting factor to bunch grape culture in these areas.

Varieties suggested for the mountains and Piedmont include: ‘Aurora,’ ‘Chancellor,’ ‘Vidal’ and ‘Villard Blanc’ for white wine; ‘Baco Noir’ and ‘Foch’ for red wine; ‘Interlaken,’ ‘Mars,’ ‘Reliance’ and ‘Saturn’ for fresh eating; ‘Concord,’ ‘Delaware’ and ‘Catawba’ for both fresh consumption and wine production.

Varieties suggested for the sandhills and coastal plains include: ‘Blanc Du Bois’ and ‘Lake Emerald’ for white wine; ‘Roucaneuf’ and ‘Black Spanish’ for red wine; ‘Daytona’ and ‘Orlando seedless’ for fresh eating; and ‘Conquistador’ for both fresh consumption and wine production.

Planting the Vine: Plant grapevines in late winter and early spring. Vigorous 1-year-old plants are best. Keep the roots moist until planting to prevent them from drying out. Pack the roots in moist, but not wet, sawdust or sphagnum moss and wrap the tops in polyethylene. Store the vines in the refrigerator until they can be planted. Planting will be easier if the soil is spaded or tilled beforehand. Dig a large enough hole to let the roots spread out naturally (root pruning is not recommended except to remove damaged roots). Plant the vines at the same depth or slightly deeper than they grew in the nursery. Keep the topsoil separate to place over and around the roots. Do not place fresh manure or fertilizer in the hole. Tamp the soil firmly around the roots and water immediately afterwards until the root zone is thoroughly soaked. After setting the vine, prune it to one stem and cut this stem back to two or three buds.

Fertilization: Establishment of proper fertility levels before planting helps get the young vines off to a good start. Grapes prefer a soil pH of 5.8 to 6.5. Test soil through the Clemson Extension Service prior to planting. After plants have been settled by a drenching rain and before growth starts, apply ¼ cup of 10-10-10 fertilizer around each plant. Keep the fertilizer at least 6 inches from the vine. Repeat at six-week intervals until mid-July.

On 2-year-old vines, double the first year rate and use the same intervals. Bearing vines will need 2½ pounds of 10-10-10 per plant applied in March. If growth is poor on producing vines, apply 1 pounds of 10-10-10 per plant in May. Foliar magnesium deficiency may become noticeable in midsummer. This deficiency is characterized by a yellowing between the leaf veins on the older grape leaves. If the soil pH is sufficiently low to warrant liming, use dolomitic lime to help prevent magnesium deficiency in future years. Otherwise, magnesium sulfate (Epsom salts) should be applied and watered in. For young plants, apply 2 ounces around each vine, keeping the salts away from the trunk 6 or more inches. Apply 4 to 8 ounces per mature bearing vine. It may require two to three years of magnesium application to bring the level up for the best plant performance.

Weed Control: For at least the first two years, keep an area 1 to 2 feet in diameter around each vine free of weeds by hoeing or mulching with compost. Once established, the vine will shade out and suppress some weeds. Recommended chemical herbicides may also be used for weed control in grapes, but mulching is the preferred management practice. Do not use the combination of fertilizer plus weed killer on lawn areas near a grapevine because the weed killer may be picked up by the grape roots and cause vine injury.

Growth & Fruiting Habit: Grape clusters form on the current season’s shoot. These shoots, on which clusters are borne, developed from buds formed on last year’s growth (1-year-old wood), which is pruned back to spurs or short canes. Shoots more than a year old are nonproductive and should be pruned. Canes, which are small in diameter, are not as productive as those of pencil size (¹/4 inch diameter). Also, thick, slightly flattened canes with widely spaced internodes (bull canes) are typically non-fruitful. As with small canes (less than ¹/4 inch in diameter), bull canes should be thinned out or headed back to one bud.

Pruning Schedule

First Year: During the first season, the primary objective for grapevine growth is the development of a large, healthy root system and a straight trunk. When new growth begins, train the two or three shoots that arise from buds on the pruned cane to a training stake. This 4- to 5-foot stake should be set 10 to 12 inches deep and should be long enough to be tied to the first wire of the trellis system. Tie the shoots loosely to the stake several times during the growing season to maintain vertical growth. On each shoot pinch back any laterals to a leaf to encourage rapid extension growth. Keep the vines well-watered and mulched to suppress weeds.

Second Year: In late winter evaluate the amount of growth produced during the first year. If no cane is long enough to reach the cordon wire, remove all but one. Prune this cane back to two buds and treat it as a first- year vine. If a cane is long enough to reach the cordon wire, relatively straight and of adequate pencil-size diameter (about ¼ inch), retain it as a trunk and remove the rest. Cut this trunk-cane through the first node above the cordon wire and tie it to the support stake.

When new growth emerges in the spring, select two shoots that are 8 to 12 inches below the cordon wire and on opposite sides of the trunk. Remove all other shoots. When these shoots reach 1½ to 2 feet in length, gently bend them over to the cordon wire and loosely tie them.

As these cordon shoots continue to grow, loosely twine them around the wire (do not wrap a shoot more than three times around a wire) and tie them. To avoid damaging the tender shoot, tie the cordon shoot at least 12 to 18 inches from the tip. When the cordon shoots have grown 5 to 5½ feet from the trunk (1 to 1½ feet beyond the halfway point to an adjacent vine), cut them back to 4 feet from the trunk, which encourages lateral shoot growth.

Low-trellis cordon system: Remove lateral shoots that develop on the underside of the cordon and retain the shoots that develop on the upper side.

High-trellis: For American labrusca bunch grapes, remove shoots that develop on the upper side of the cordon and keep the shoots that develop on the underside. For American non-labrusca and American hybrid bunch grapes, prune out shoots that develop on the underside of the cordon and retain shoots that develop on the upper side.

With either system, rub off all flower/fruit clusters as they develop and maintain a good pest control program to protect the leaves.

Third Year: The objective of the third growing season training is to establish vertical arms on each cordon.

Low-trellis: In late winter, head back canes that developed on the upper side of the cordon to spurs of one to three buds. Space the spurs at regular intervals of 4 to 6 inches. Remove all extra shoots and suckers arising from the trunk. When new growth begins, rub off any shoots that develop on the underside of the cordons. Tie the selected vertical shoots to the first catch wire as soon as they reach a length of 18 inches. The sole purpose of the catch wire is to direct the shoots upward. Later in the growing season, head back or hedge the shoots above the top catch wire. Ideally, these shoots should be 4½ to 5 feet long with 15 to 20 leaves.

High-trellis: For American labrusca bunch grapes, retain short canes of four to six buds on the lower sides of the cordons to promote downward growth. Space them at regular intervals of 4 to 6 inches along the cordon. For American non-labrusca and American

hybrid bunch grapes, retain spurs of one to three buds or short canes of four to six buds on the upper sides of the cordons. Train the shoots downward to create a “curtain.” Altering the canopy in this manner will improve light interception by the leaves, and most important, will expose the basal four to five buds of the shoots to sunlight. These are the buds that will produce next year’s crop, and the exposure to light will increase their fruitfulness.

During the third season, it is very important to prevent the vines from overproducing. Allow only one cluster of fruit per two shoots to balance fruit production with the accumulation of food reserves in the vine. Continue to maintain a good pest control program.

Fourth Year & Thereafter: The vine must be pruned each year during the dormant season to avoid alternate-bearing and to make harvesting easier. Pruning after growth starts may cause an excessive flow of sap from the cuts. In fact, “bleeding” may occur at pruning in midwinter if fine roots have been stimulated into growth following warm weather. This loss of liquid is not injurious to the vine.

Pruning the mature vine consists of three operations:

• The first step is pruning last season’s growth. Evaluate the canes that developed from last year’s spurs. Select straight canes, that developed from basal spur buds (closest to the cordon) and are growing in the right direction for the particular training system. Head back these canes to spurs or short canes as was described in the third year for each system. They should be spaced 4 to 6 inches apart along the cordon.

• The second step is to remove water sprouts, suckers, and any tendrils attached to the trunk or cordons.

• Finally, prune back cordon growth beyond the 4- foot point or halfway to the next vine. Do not retain any canes on the bends or divide of the cordons.

For both the low- and high-cordon systems, maintain four to six shoots per foot of cordon, removing shoots where necessary. Also, selectively remove leaves from around the fruit clusters to improve fruit quality and help reduce disease pressure. These leaves can be removed shortly after bloom but before the berries begin to change color and soften (the verasion stage). Do not remove the leaves after the berries begin to soften because sunburn may result.

Overcropping will greatly reduce fruit quality and will reduce next year’s harvest by limiting food reserves in the vine. Some cluster thinning in years of heavy fruit set (thinning to one or two clusters per shoot) is the simplest way to ensure that those remaining fruits will develop into larger, more fully ripened clusters. A good rule-of-thumb for mature vines is to allow no more than two clusters per shoot.

Harvesting

An acceptable taste is the main criterion for table use. On a vine that is not overcropped, the berries of black varieties lose their red color and white varieties will change from green to golden yellow. Ripe berries will soften and seeds become brown. Determining the harvest of wine grapes requires either experience or a means of measuring both sugar and acid content.

Diseases & Insects

Since bunch grapes are susceptible to a number of diseases and are attacked by several insect pests, a season-long spray program may be necessary to produce good fruit. Refer to the Pest Management Handbook, Vol. 1, EC 670, for control recommendations.

Pierce’s disease, which is very common in the sandhills and coastal plain, is a bacterialike disease spread by leafhoppers that kills susceptible bunch grape varieties. Special varieties should be grown in the sandhills and coastal plain for the vineyard to live for more than three years.

Downy mildew is a fungal disease, which causes yellow spots on upper leaf surfaces and white, cottony growth on the undersides of the spots.

Black rot is a fungal disease, which causes brown leaf spots with dark borders and black, shriveled grapes, which remain attached to the stem.

An important insect pest that deserves special attention is the grape root borer. It is very difficult to control and can destroy entire vineyards. The adult grape root borer is a moth that resembles a wasp. From July through October it can be found flying and laying eggs on grape leaves. Larvae drop from eggs down to the soil where they begin feeding on the small feeder roots, and eventually move into the crown of the grapevine during its two-year larval stage. Infested vines lose vigor and usually die. Larvae pupate just below the soil surface and adults emerge from the soil directly beneath the grapevine from July through October.

Cultural control measures include mounding soil directly beneath the vines in late June or very early July to prevent adult emergence. A landscape fabric (geotextile weed barrier) may be an alternative to mounding soil. These materials are porous and will allow water penetration, but the weave is too tight for adults to pass through. While these cultural controls can eliminate the adults, they offer no control of moths flying into the vineyard and laying eggs on the leaves. The larvae may be able to reach the roots through the landscape fabric.

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This popular small fruit bears plenty of berries that are delightful when eaten fresh or used in pies, muffins, pancakes or as a fruit topping for breakfast cereals. Also, blueberry plants add beauty to the landscape when grown in beds, rows or as a hedge along the property border. Blueberry-growing presents a challenge because the plants require soils that are acid, well-drained, loose and high in organic matter. These types of soils are not common in most areas of the state. However, blueberry plants can be very long-lived (25 years or more), so the considerable time and expense in preparing the soil is well worth the effort.

Recommended Varieties

There are three main types of cultivated blueberries that can be grown in the Southeast: rabbiteye, Northern highbush and Southern highbush. This section focuses on the rabbiteye and Southern highbush types.

In general, rabbiteyes (Vaccinium ashei) are the most adaptable, productive and pest-tolerant of the three types of blueberries. Except for higher mountain elevations, rabbiteye cultivars are adapted to all of South Carolina. In general, rabbiteye blueberries have some degree of self-incompatibility; therefore, a minimum of two varieties is required for cross-pollination to ensure maximum fruit. The following rabbiteye cultivars are recommended in South Carolina: Early season: Beckyblue, Bonita, Brightwell, Climax, Premier, Woodard; midseason: Bluebelle, Briteblue, Chaucer, Powderblue, Tifblue; late season: Baldwin, Centurion, Choice, Delite. Woodard is a good berry for fresh-eating but develops a tough skin when frozen. Tifblue, Powderblue, Brightwell, Briteblue and Centurion are most resistant to spring freezes. Bonita, Climax, Woodard, Beckyblue, Chaucer, Choice and Delite are not recommended for the mountains.

Southern highbush blueberries are hybrids derived from crosses between Northern highbush blueberries and native Southern species, mainly Darrow’s evergreen blueberry (V. darrowi). Southern highbush cultivars, in

addition to lower chilling requirements, also have greater tolerance to high summer temperatures, somewhat greater drought tolerance and develop superior fruit quality under Southern growing conditions. As a rule, Southern highbush blueberries are self-fertile. However, larger and earlier-ripening berries result if several cultivars are interplanted for cross-pollination. The following Southern highbush blueberries are recommended for the garden and landscape: Very early season: O’Neal; early/midseason: Cape Fear; midseason: Blue Ridge and Georgia Gem (adapted to the Sandhills and Coastal Plains; needs frost protection in the Piedmont); mid/late season: Legacy and Summit; late season: Ozarkblue (Piedmont only).

Plant Growth Cycle & Yields

Two-year-old bare-root nursery plants 1 to 3 feet tall are transplanted in late winter or early spring. Potted plants can be transplanted in late fall. Growth begins with bud swell in the spring and continues into late summer and fall. The blueberry produces several flushes of rapid shoot growth. Each growth flush ceases when the uppermost or apical bud aborts (this is not a disease). Soon after, a bud “breaks” near the tip to begin another flush of shoot growth. Each shoot may experience several of these growth flushes during the season, and each flush may result in 6 to 10 inches of growth with adequate moisture and nutrition. Shoot growth usually stops in midsummer.

Typically, five to eight flower buds can develop on a healthy shoot. Each flower bud can produce from five to 10 flowers that continue to develop inside the bud throughout the fall and early winter months. Both vegetative and flower buds become dormant in winter. Flower buds open sequentially in the spring, with the flower buds on the tip of the cane opening first. The flowers inside a bud open up in a similar sequence with the flower nearest the tip opening first. Shoot thickness affects blooming sequence, with blossoms on thinner wood opening up earlier than buds on thicker wood.

It is best to remove all flower buds in both the first and second years after planting to stimulate good shoot and root development. Blueberry flowers and fruits sap considerable energy from the plant, and fruit yields in subsequent years can suffer because of poor plant development in the first two years of establishment. In addition to removal of the flower buds, head-back the top one-third to one-half of all shoot growth on rabbiteyes at the time of transplanting.

Blueberry fruit ripens over a two-month period after bloom. This will vary with the cultivar, weather conditions and plant vigor. Plants should produce about a half-pound per bush in the third year, and 1 to 2 pounds per bush in the fourth year. With good care, mature Southern highbush plants can produce more than 8 pounds of fruit each year. Rabbiteye can produce 12 to 25 pounds.

Culture

Soil pH Adjustment: Have a soil test taken in the fall before planting in late winter or early spring. If the pH is above 6.0, select another planting site. If the soil pH is below 6.0 but above the 5.5 limit, apply wettable sulfur (90 percent sulfur) or aluminum sulfate. A very low soil pH caused by excess sulfur can be detrimental. Some soils in the Piedmont are very high in manganese. When growing blueberries on these soils, keep the pH above 5.0 to avoid problems with manganese toxicity. Any sulfur applications should be made at least three months prior to planting because it takes several months for sulfur to reduce the pH. Check the pH once or twice during the first growing season to determine if still more sulfur is required later in the season.

Sometimes, the impatient home gardener will insist on planting without a soil test. In this case, mix 1 cubic foot of peat moss with an equal amount of sand. It is important to use a sand that has not been limed or that does not contain a liming material. Most builder’s sand, referred to as “sharp” sand, does not contain liming materials.

Soil Water Drainage: On a heavy clay soil or a soil that sometimes remains wet, apply the peat-sand mixture to the soil surface and plant. If the soil has good drainage, part of the peat-sand mixture can go in a hole or furrow several inches below the soil surface. However, leave enough of the peat-sand mixture to form a mound (for single plants) or a ridge (for a row of plants) at least 6 inches above the surrounding soil surface. The mound or ridge will protect plants from excess water; however, with this method of planting, water thoroughly two to three times per week during dry spells in the summer and early fall. Logs, landscape timbers, stones, bricks or concrete blocks can be used to contain the soil mixture in the raised bed.

Preplant Additions of Organic Matter: Blueberries are naturally adapted to high organic matter soils where soils have 3 percent or more organic matter as opposed to most mineral soils with organic contents usually less than 1 percent. Organic materials such as peat moss, composted pine bark or rotted softwood sawdust should be incorporated in soils of less than 2 percent organic matter prior to planting to greatly improve blueberry plant survival and growth. Hardwood sawdust is not as effective as softwood sawdust or peat moss for lowering soil pH. Undecomposed softwood sawdust should not be used.

Follow this popular step-by-step pre-plant program to modify soils with less than 2 percent organic matter:

1. Establish the plant mounds or ridges (3 feet wide) to provide the required drainage on poorly drained soils;

2. Apply 4 to 6 inches of organic matter over the row in a band 18 to 24 inches wide and incorporate thoroughly using a rototiller or spade to a depth of 6 to 8 inches;

Steps 1 and 2 should be completed in the fall prior to planting in late February to late March, depending on location. If the organic matter is incorporated in the fall, any sulfur required to lower the pH can be added at the same time.

Note: Water and nutrient management is difficult in pure organic material, and the plants are more likely to struggle and die.

Planting

Plants: Two- or 3-year-old nursery plants 1 to 3 feet tall will transplant well. Keep the roots moist at all times between digging and replanting.

Time: Late winter (February-March) as soon as the soil can be worked is best for bare-root plants; fall (November-December) planting has been successful on sandy soils with bare-root plants and in other areas with potted plants.

Spacing: Southern highbush – 4 to 5 feet in the row and 8 to 10 feet between rows. Rabbiteye – 6 feet in the row and 10 to 12 feet between rows.

Depth: Plant to the same depth as the plants were growing in the nursery. Lightly firm the soil around the plant with your feet and water thoroughly.

Cut Back: Remove all shoot tips that have flower buds (plump rounded buds). Avoid making cuts near the base of the plants that will provide an entryway for stem

blight disease. To enhance survival and subsequent growth and development, prune away two-thirds of the top growth on bare-root and one-half on potted plants. Leave only one to three of the most vigorous upright shoots and any other growth near soil level.

Surface Mulch Application: Organic material such as bark, wood chips, sawdust or pine straw as a 2- to 3-inch mulch on the surface after planting results in more uniform soil moisture, moderates soil temperature and generally promotes better growth and survival. Pine bark chips or sawdust have a pH between 3.5 to 4.5 and are more desirable than the same mulches from hardwoods with a pH above 5.0. However, surface-applied hardwood mulches have been satisfactory. Avoid sticky hardwood sawdust that will “seal” the bed and prevent water infiltration.

Fertilization

Use Caution: Blueberries are easily damaged by excess fertilizer. Apply the recommended amount and allow 4 inches of rain or an equivalent amount of irrigation between applications.

First Year: Do not fertilize immediately after planting. Wait until the first leaves have reached full size, then apply 1 tablespoon of a 10-10-10 fertilizer within a circle 18 inches away from each plant. Repeat at about six-week intervals depending upon rainfall or irrigation until mid-August in the Sandhills and Coastal Plain and mid-July in the Piedmont. Use a half-tablespoon of ammonium nitrate instead of a complete fertilizer for the second and subsequent applications if high levels of phosphorus are present as determined by a soil test.

Second Year: Double the first year’s rates, but increase the circle around the plants to 2 feet. Make the first application when new growth begins in the spring.

Bearing Plants: When growth begins in the spring, apply 1 cup of a complete fertilizer such as 10-10-10 within a circle 3 feet from each plant. For more vigorous growth, sidedress with a quarter-cup of ammonium nitrate at six-week intervals, but stop fertilizing after July 1. On mature bushes, 6 to 12 inches of new growth is adequate. Any additional growth must be pruned away to keep the plants from becoming excessively large and resulting in a loss in production. Judge the sidedressing requirement on the amount of shoot growth and leaf color.

Lowering pH: If the soil pH is slightly high in an established planting based on soil test results, sidedress with ammonium sulfate instead of ammonium nitrate.

Cultivation

If mulch is applied following planting and replaced at the rate of 1 inch per year, few weed problems should develop. Handpull or hoe the occasional weed growth. Avoid deep cultivation since blueberry roots are very near the surface. Hoe no more than about 1 inch deep.

Pruning

Since blueberries are produced from buds on 1-year-old wood, pruning should be severe enough to encourage the production of vigorous new growth each year. Because rabbiteye blueberries are vigorous and can support and develop heavy crops of large-sized fruit, they generally require less pruning than southern highbush blueberries. During the first five years little pruning will be required. Remove lower twiggy growth, dead or damaged shoots, and weak, spindly growth. Tip back excessively long and limber shoots to stimulate lateral branching and to thicken the shoots. Prune young plants during the dormant season and immediately after harvest with older plants.

If plants become too tall to harvest easily, selectively remove about one-third of the older canes in the winter. Generally up to seven canes are left each year after pruning mature rabbiteyes, with the oldest or largest cane removed each winter beginning in the fifth year. These selective cuts should be made to open up the center of the plant to improve light penetration and to allow new canes to develop to replace old canes.

Southern highbush blueberries require annual pruning to prevent overbearing and to maintain vigor. Prune during the dormant season; late winter is most desirable, especially in the mountains.

If the flower buds were removed after planting, little pruning will be required the second year except to remove all flower buds and any weak, damaged or diseased growth. After two growing seasons, leave some flower buds on vigorous shoots to produce a small crop in the third year. To prune bearing-age plants, remove low spreading branches and branches growing through the center of the bush, especially weak and older branches. Cut back extremely vigorous 1-year-old shoots and remove most small slender branches. If earliness is important, remember that berries produced on small slender laterals will usually be the first to ripen, so this should be taken into account in determining the number of these shoots to remove. Also, long-fruiting lateral shoots need to be tipped back so that no more than four to six flower buds remain.

Highbush blueberry plants generally reach their peak production between 8 and 10 years of age. To maintain bush vigor with the continued production of high-quality fruit, renewal pruning must be practiced. Begin the renewal process when the bushes are about 6 years old. First, remove any weak or diseased canes entirely. Among the remaining canes starting with the older ones, cut back about two per year either to strong lateral branches or to within 1 foot of the ground. New strong lateral branches will usually develop below the cut. Through renewal pruning, a new upright framework can be developed over a four- to five-year period.

Problems

Blueberries may be troubled by fungal leaf spots, fruit rots, root rot and gray mold. The primary insect problems are cranberry fruitworm (which ties berry clusters together with silk), Japanese beetles and the Oberea stem borer.

Harvest

Bird Protection: Birds also harvest blueberries, often the complete crop from a small planting. Plastic or cloth netting draped over the bushes or supported on a framework is the only practical control.

Frequency: Southern highbush blueberries have the best quality when picked every five to seven days depending on temperature. Rabbiteye flavor improves if berries are picked less often, about every 10 days, which allows for maximum flavor with few soft overripe fruit.

Important stages in the development of fruit and vegetative growth in blueberries: (A) dormant stage after leaf drop showing one flower bud; (B) blooming stage that shows the cluster of flowers and vegetative shoot that developed from the top two buds of the dormant stage; (C) fruit set stage where pollinated flowers begin developing into small fruits; (D) fruit development stage that extends from fruit set to mature fruit. Both flower and vegetative buds for the next season are often easily recognized on vegetative shoots at the time fruit ripens.

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Blackberries are divided into classes by their growth habit and are described as trailing, semi-trailing or erect. The trailing varieties (sometimes called dewberries) are thorny; the semi-trailing varieties are thornless; and the erect varieties may be thorny or thornless. As a rule, the erect varieties are more cold-hardy than the trailing or semi-trailing varieties (see table, next page). Erect varieties also fruit about one month earlier than other varieties.

Planting

The semi-trailing varieties should be planted 6 to 8 feet apart in the row, with rows 10 feet apart. The trailing types are less vigorous and should be planted about 4 feet apart, with rows 6 to 8 feet apart. Erect varieties are usually established by planting root cuttings. Plant these cuttings about 2 feet apart. Plant blackberries in early spring, about 4 to 6 weeks before the last frost.

When planting, make sure the crown is about 2 inches below the soil line. Carefully spread the roots. If there is a portion of an old cane attached as a “handle,” prune that back to 6 inches. When planting root cuttings, place the cuttings in a horizontal position and cover 4 to 6 inches deep in sandy soils or 3 to 4 inches deep in clay soils.

Mulching & Watering

Mulch with the material of your choice. Mulch aids in water retention and weed control. Blackberries are quite drought-hardy, but require considerable water during the fruiting period. Apply about 1 inch of water per week by irrigation if rainfall does not meet the need.

Fertilization

Fertilize blackberries in early spring when growth starts and again just after harvest. A complete fertilizer such as 10-10-10 is satisfactory. Apply at the rate of 5 pounds per 100 feet of row. A pint of fertilizer weighs about 1 pound.

During the first year or two of growth, apply the fertilizer in a 12-inch circle around the plant. On older plants, broadcast the fertilizer down the row.

Pruning & Training

The first step in pruning blackberries is to understand their growth cycle. Blackberries have crowns that produce biennial shoots (live for 2 years, then die). During the first year of growth the shoots are called primocanes. These primocanes develop flower buds the first year of growth. In the second year the shoots are called floricanes. These floricanes produce flowers that mature into fruit. After fruiting these floricanes die and should be removed.

Support trailing and semi-trailing varieties by a trellis or similar structure. A two-wire system, with wires at 3- and 5-foot heights, works well. As the shoots emerge in the spring, tie them to the wires in a fan-shaped pattern. Do not top the canes during the growing season. Prune out and discard the old floricanes during the dormant season. It will be obvious which canes are the dead floricanes.

Erect varieties do not need support if the primocanes are pruned during the summer to keep the canes from growing more than 3 to 4 feet in height. Train unpruned erect varieties to a one-wire trellis. When the new shoots are 30 to 36 inches tall, cut off the tips to promote branching.

Following harvest, cut and remove all floricanes. Continue to tip primocanes at this time. During the winter, prune the laterals to 12 to 14 inches for easier harvesting and larger berries.

Harvesting

The berries are ripe and at peak flavor when they begin to lose their glossy shine and turn slightly dull. Trailing and semi-trailing varieties begin to ripen in late June in the Piedmont, one to two weeks earlier in coastal areas and one to two weeks later in mountainous areas. Erect varieties are about two weeks earlier than trailing or semi-trailing varieties. Harvest should cover two to three weeks.

Problems

Insect problems on blackberries are minimal. Pests like aphids, Japanese beetles and spider mites can be controlled on an as-needed basis with general pesticides. Crown borers can be a serious pest.

Blackberry Varieties for South Carolina

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