Juanita Popenoe and Richard K. Zimmerman
Blueberries can be grown in most parts of West Virginia with attention to a few requirements. The crop has potential for excellent returns especially if marketed in large metropolitan areas. The wild blueberries and huckleberries (Vaccinium and Gaylussacia spp.) that can be found in many parts of West Virginia are species that are not grown commercially. This circular explains the culture of the highbush blueberry (V. corymbosum) which is the species commonly grown commercially in the north. The rabbiteye blueberry (V. ashei) is similar to the highbush blueberry but grows only in warmer areas.
The natural vegetation of a site is an indication of the suitability of the site for blueberries. Wild blueberries, huckleberries, azaleas, laurel, native spiraea or hardhack are all plants that grow on soils adapted for blueberries. If your soil is not suited, several measures must be taken for a successful planting.
Proper site preparation should begin one year prior to planting. Soil tests, perennial weed control and organic matter incorporation in the planting strips should be priority measures for the new planting. Blueberries require soils high in organic matter, therefore, additions of well rotted sawdust may be mixed with the soil in the planting hole. These materials are also useful as mulch around the plant to control weeds and conserve moisture. Six inches of mulch should be applied at planting and at least an inch replaced annually to the soil around the plants.
Blueberries have shallow roots and require frequent irrigation, but they do not like having wet feet, so be sure the soil is well drained. If the soil is not well drained, hilling the planting row a foot or so above the aisle will help keep the roots out of standing water.
Blueberries grow in acidic soil in a range of pH from 4.0 to 5.2 with the optimum from 4.5 to 4.8 Soil more alkaline than this can be corrected by the addition of sulfur. If ferrous sulfate is used to increase acidity, multiply the number of pounds indicated for sulfur by 6. Table 1 will help you adjust most soils by using sulfur.
Preparing the soil for planting is much the same as preparing for a home garden. To find out the pH and fertility of your soil, have the soil tested prior to planting by the West Virginia University Soil Testing Lab. It is a free and valuable service. Cover crops or legume sod should be tilled in late fall or early in the spring. Any fertilizer recommendations from the soil analysis should be added and mixed in with the soil in the spring when the soil is worked up for planting. After planting, no fertilizer should be applied until growth has started. Apply 10-10-10 at 100 lbs/A (2 1/2 lbs/100 ft row, or 2 oz/plant) when growth starts, and a further 100 lbs/A of ammonium sulfate six weeks later. The second year, apply 10-10-10 at 200 lbs/A and two applications of ammonium sulfate at 100 lbs/A and two applications of ammonium sulfate at 100 lbs/A at 6-week intervals. The third year, apply 10-10-10 at 300 lbs/A plus the two applications of ammonium sulfate at 6-week intervals. The fertilizer application should be increased each year until mature bushes (six years) are receiving about two pounds per plant per year. These amounts should be halved if no mulch is applied. The fertilizer should be applied in a uniform application over the mulch. Fertilizers with 2% magnesium oxide (represented by a fourth number such as 10-10-10-2) are recommended.
Table 1 Changing Soil pH with Sulfur
One of the most common deficiency symptoms seen in blueberry is iron chlorosis. This is characterized by a yellowing or interveinal chlorosis of the leaves while the veins remain green. Symptoms first appear on the young shoots. Only in advanced stages is the yellowing seen on older leaves. Iron chelate worked into the soil around the base of the plant or applied to the leaves are a foliar spray should eliminate these symptoms within a month. Other possible deficiency symptoms should be analyzed by your extension agent or diagnosed by tissue analysis.
Order the plants as far in advance as possible to ensure you get large plants of the desired cultivars. Highbush cultivars should be selected to allow a range of harvest dates so that harvest labor can be spread out (see Table 2). More than one cultivar is suggested to provide cross pollination which results in larger berries.
When the plants arrive, refrigerate at 33-36 oF, or open a trench, space the plants along the side of the trench and cover the roots with soil to prevent them from drying out. Plant the blueberries in the spring as early as possible. A furrow may be opened down the row or individual holes may be dug. If organic matter is to be added, it may be spread out and rototilled in, or mixed with the soil of individual planting holes. The blueberry roots should be spread out in the hole or furrow and the soil replaced and firmed about the plant. The plants should be watered-in immediately and tops pruned back 1/2 to 2/3.
The plants should be set four to five feet apart with enough room between the rows to allow equipment to pass. The plants should be set in a weed free strip at least three feet wide. The aisles between the rows can be grassed, but be careful to use bunch rather than rhizomatous grasses which will quickly grow into the weed free strip.
Pruning is essential to produce large berries and vigorous plants. For the first two years the flower buds should be pruned off the plant to allow it to become established. The natural growth habit of the blueberry is to branch with each successive branch getting thinner. The fruit is produced only on growth from the previous season. The best fruit is produced on strong wood that is about pencil thick. Once the branches get too thin to have good fruit, that whole cane should be removed at the soil level. Renewal shoots coming from the base of the plant should be encouraged to replace the current fruiting wood. Canes usually should not be kept more than five years. Try to keep about equal numbers of one-, two-, three-, four-, and five-year-old canes. Weak or sprawling canes and diseased canes should also be removed. Try to keep the canopy open to intercept the maximum amount of light and allow air to circulate.
Pick the berries in the morning at five- to seven-day intervals starting a few days after they turn blue. Avoid dropping the berries more than two or three inches when they are picked and packaged. Picking the berries directly into pint containers for sale is the best method because it reduces handling. Handling tends to cause bruises and damage to the 'bloom' or waxy finish. A good picker should be able to pick up to 240 pints per day under good conditions. Mechanical harvesting with a bush shaking machine is a possibility, but some berry bruising will result and some cultivars will drop all their berries, green and ripe, when shaken.
The picked berries should be refrigerated immediately until used or shipped. Fresh harvested berries can be held over two weeks at 32o F but only for two days at 70o F. Variation of temperatures in storage can cause condensation of moisture on the fruit and early spoilage.
Mummy Berry is caused by a fungus (Monilinia vaccinii-corymbosi). The fungus overwinters in mummified berries that have fallen to the ground. With moisture in the spring, these mummified berries produce small, brown, cup-shaped fruiting bodies that produce spores carried by the wind and insects to the young, succulent shoots. Sod or moss directly under the plant will contribute to the spore production. The infected shoots will curl up, turn brownish black and die. The fungus in the twig then produces a second kind of spore that infects the newly forming berries. The berries will not show signs of the infection until the other berries start to turn blue. At this point, the infected berries will turn beige-brown and start to shrivel to a mummy. To control this fungus, rake and burn the mummified berries, or cover over the fallen berries with at least two inches of mulch. Cultivation during the moist spring weather will destroy the spore forming bodies in the spring. Another technique is to apply urea and sand (50/50) at the rate of 200 lbs. per acre in the spring when the cup-shaped fruiting bodies appear.
Stem cankers can be caused by many fungi. The symptoms are similar. Cankers appear at first as discolorations on the stem, but then grow in size often girdling the stem. With hot, dry weather, the whole stem may suddenly wilt and die. Vigorous, healthy bushes should be resistant to these attacks. To keep your plants from succumbing, eliminate weeds around the plant and remove and destroy any unhealthy or dead wood. Fungicides may also be used.
Most fungal diseases can be controlled by removing and burning the diseased wood, fruit or leaves. If there is a continuing problem, contact your extension agent.
Virus disease symptoms include stunted, yellow plants and leaf spots with rings of red. The only control for these is complete removal and destruction of the plant as soon as symptoms are noticed. Control of sucking insects that transmit the disease is also helpful.
There are few insects that have been found to be a problem in blueberry plantings in West Virginia. The blueberry maggot has been found in a few fruit some years, and WVU is currently working on a nonchemical control method.
Birds will be attracted to the fruit as soon as it turns blue. The only current recommendation is to cover the plants with bird netting. No chemicals are registered for use and other scare devices have not proven to be effective.
Table 2. Highbush Blueberry Cultivars