Commercial Blueberries

David Himelrick, Extension Horticulturist

Larry M. Curtis, Extension Agricultural Engineer

Blueberries are grown in various parts Of Alabama, with the most extensive plantings found in south Alabama and in the Clay County area. Blueberry bushes grow and produce best in acidic soils (pH from 4.2 to 5.5) with relatively constant soil moisture. Thus blueberries have significant potential for commercial production in Alabama, where naturally low-pH soils and plentiful water for irrigation are found.

Irrigation removes the risk of crop yield or quality losses caused by uneven distribution of rainfall during the growing season and makes possible the consistent production needed for long-term marketing success. In addition, irrigation is essential for the establishment and survival of young plants, and generally increases the yield of mature plantings from 25 to 40% above non-irrigated plantings. The economic justification for using micro-irrigation in blueberries is good, since micro- uses as little as half the energy and water needed for overhead sprinklers, which means lower initial and operating costs. However, a major disadvantage of micro-irrigation for blueberries is its limited frost protection capability (discussed below).

Blueberry Irrigation Benefits

For a new planting, irrigation can spell the difference between success and failure in establishing the planting. While mature blueberry bushes are relatively drought-resistant, bare-root or container-grown young plants have a limited root system and are especially susceptible to drought stress. Even when the surrounding soil is still wet after a heavy rain, the newly-planted blueberry bush may be experiencing extreme stress. To avoid such stress, the irrigation system should be ready for operation at planting time.

In the first two years, irrigation speeds establishment and growth of uniform and healthy plants, and a small first crop may be harvested in the second year. Without irrigation, the first harvest usually takes three or more years.

Irrigating during the growing season before harvest produces larger berries and higher yields. Post-harvest irrigation contributes to increased growth and fruitbud formation that can provide higher yields the following year. Highbush varieties, including the adapted southern highbush, particularly need a well-drained soil but also especially benefit from the consistent soil moisture provided by irrigation.

Water Quality

Blueberry plants are especially sensitive to water quality, and growers should have water tested before establishing the planting. The most significant water quality hazards are high pH and salinity (high concentration of mineral salts). The most helpful salinity hazard indicator is electrical conductivity (EC). Water for blueberry irrigation should have an EC below 1.0 mmhos/cm. Salinity problems are found in only a few, scattered locations in Alabama and are not usually encountered where irrigation water is drawn from ponds or streams. If salinity build-up is a potential problem, irrigation should be scheduled in smaller, more frequent applications.

Alkaline (high pH) irrigation water will eventually raise the soil pH to a level harmful to blueberries. Also, high pH water is more likely to contain potentially harmful levels of salts, sodium and carbonates. Water sources with pH consistently above 6.5 are not recommended for blueberry irrigation, since continuous acid injection would be required to lower pH to an acceptable level.

For more information, see Circular ANR-649, Water Quality, and ANR-652, Acid Injection, in this handbook.

Water requirements

Mature blueberry bushes have a peak water requirement of 6-8 gallons per plant per day. In most cases, blueberry irrigation systems should be designed to provide a peak need of 8 gallons per plant per day. With 6' x 12' plant spacing and 605 bushes per acre, this translates to a system pumping capacity of 4,840 gallons per acre per day, or about 1.25 inches per acre per week.

Younger plants need less water according to size, with 3- to 4- foot plants having a peak requirement of about 3 to 4 gallons per plant per day, and new plantings from .5 to 1 gallons per day. CAUTION: Newly-planted blueberry bushes have small root systems and are very susceptible to drought stress.

Because blueberries have shallow root systems, usually less than two feet deep, they will experience drought stress sooner than will deeper-rooted species. For this reason, the water-holding capacity of the soil is an important factor, and not only the total amount of water applied but the coverage pattern and frequency of application must be appropriate to ensure that adequate water is actually available to the plants' root systems.

Systern Design Options

Blueberries can be successfully irrigated using any of the common micro-irrigation methods (drip tape, drip emitters, or spray/stream emitters), or with permanent, solid-set overhead sprinklers.

Overhead sprinklers have the advantage of being able to provide significant frost protection, but are more costly to install and operate, using much more energy and water. If it is to be used for frost protection a sprinkler system must be over-designed as an irrigation system. That is, the system must be capable of watering the entire planting at .2 inches per hour or more, depending on the level of frost/freeze protection needed. Another disadvantage of sprinklers is that repeated wetting of the bushes can encourage disease.

Spray type micro- erriitters are preferred for irrigation on sandy soils because their larger wetting pattern reaches a larger percentage of the root system. One spray or sprinkler-type micro- device can be used in the row for every two bushes. These devices require somewhat less maintenance than drip emitters, and can provide limited frost protection.

Drip emitters are well suited to young plants with limited root systems, giving better water-use efficiency. If drip emitters are used for mature plants, the wetted area should cover 50% of the root zone. On clay and clay loam soils with high water-holding capacity where drip emitters have a wetted width of over 6 feet, one emitter per plant can be used. On sandy soils, single drip emitters will not wet an adequate percentage of the plant root zone. Drip tape, with emitters every 6 to 24 inches, has the smallest initial cost but also has a short useftil life. For new plantings a possible option is to use drip tape in the first year or two, replacing it with other lateral lines and emitters when bushes are larger.

Frost Protection

Frost protection measures are essential for reliable high-retum blueberry production. Early flowering varieties which ripen their fruit early in the season when market prices are highest are also more susceptible to frost damage than varieties that bloom later. Early flowering varieties commonly grown include rabbiteyes such as 'Climax' and low chilling southern highbush varieties.

Choice of an irrigation system is determined, therefore, not only by irrigation considerations but by the extent of frost protection deemed necessary and by cost-and-retum calculations for the particular situation. overhead sprinklers generally offer the best frost protection, while micro- systems offer water and energy savings. A dual system using sprinklers for frost protection and micro- for irrigation may be cost-effective in some situations, especially where a tractor PTO can be used to power the sprinkler system pump.

Protecting blueberries from frost or freezing is by its nature an uncertain undertaking, with too many variables for firm predictions. Information presented here is based on generally accepted research findings and grower experience, but can be used only as a general guide for decision making.

If there is no wind, overhead sprinklers delivering .2 inches of water per hour to the entire planting usually can give freeze protection down to around 22°F to 24°F. Application should begin when air temperature reaches 34°F and continue until the air temperature goes above 32°F and all ice on plants has melted. CAUTION: If air temperature drops into the low 20s or below or if wind is higher than 5 mph, sprinkling can cause more damage than not sprinkling. NOTE: Basic requirements for frost-freeze protection with sprinklers are outlined in the appendix of the Alabama Micro-Inigation Handbook.

Micro- spray systems may provide several degrees of freeze protection on a still night. Protection is enhanced by one or two degrees under calm conditions if the soil is bare, firm, moist earth instead of gram or another cover. Insulating row covers used with micro-spray systems provide protection comparable to that given by overhead sprinklers. However, row covers are expensive both in initial cost and in labor and are not practical under high wind conditions.

Scheduling

Because of their shallow root systems, blueberries should be irrigated at least twice a week under dry conditions. More frequent applications of smaller amounts are needed on lighter soils. Soil moisture should be monitored--see Circular ANR-647, Scheduling, for more information on irrigation timing and water management methods.

CAUTION: Too much water can be a problem. If free water stands for more than 5 days, blueberries may suffer permanent damage from water-logging. on heavy soils with poor drainage, plantings should be on raised beds.

Fertilization Under Micro-Irrigation

In general, irrigation allows for more fertilization than non-irrigated culture, making applications possible in summer months when dry conditions would otherwise prohibit fertilization. Injection of water-soluble fertilizers through the micro- system allows application of small amounts of fertilizer at intervals throughout the season, with less loss from leaching in comparison with other fertilization methods. This practice---called fertigation-is especially suited to blueberries since they are highly sensitive to excess fertilizer. See Circular ANR-653, Applying Fertilizers Through the System.

Acid-forming fertilizer materials such as ammonium sulfate can be beneficial in lowering soil pH in situations where soil or irrigation water pH is higher than desirable. Ammonium forms of nitrogen (not nitrates) should be used on blueberries. A typical fertigation schedule might include periodic injections from March through September. For example, a grower might apply 150 oz of urea or 300 oz of ammonium sulfate per acre per week on a mature planting. Plantings less than 6 years old would receive proportionally less nitrogen with first year plants getting 50 oz of urea or 100 oz of ammonium sulfate.

References

Anderson, P.C. et al. 1979. Water relations and yields of three rabbiteye blueberry cultivars with and without drip irrigation, J. Amer. Soc. Hod. Sci. 104 (6): 731-736.

Davies, F.S. and C.R. Johnson. 1982. Water stress, growth, and critical water potentials of rabbiteye blueberry, J. Amer. Soc. Hort. Sci. 107(l):6-8.

Haman, D.Z. et al. 1988. Blueberry response to irrigation and ground cover, Proc. Fla. State Hort. Soc. 101: 235-238.

Krewer, Gerard et al. 1989. Commercial Blueberry Culture. Circular 713, Georgia Cooperative Extension Service, University of Georgia.

Lyrene, P.M. and T.E. Crocker. 1991. Commercial Blueberry Production in Florida. SP 97, Florida Cooperative Extension Service, University of Florida.

Patten, Kim. 1988. Irrigation, in Texas Blueberry Handbook. Texas Agricultural Extension Service and Texas Agricultural Experiment Station, Texas A&M University.

Puls, Earl, Jr. 1989. Commercial Blueberry Production. Pub. 2363, Louisiana Cooperative Extension Service, Louisiana State University.

Spiers, J.M. et al. 1985. Establishment and Maintenance of Rabbiteye Blueberries. Bulletin 941, Mississippi Agricultural and Forestry Experiment Station, Mississippi State University

Tyson, A.W. No date. Irrigating Blueberries. Georgia Cooperative Extension Service, University of Georgia, Statesboro.

Issued in furtherance of Cooperative Extension work in agriculture and home economics, Acts of May 8 and June 30, 1914, and other related acts, in cooperation with the U.S. Department of Agriculture. The Alabama Cooperative Extension System (Alabama A&M University and Auburn University) offers educational programs, materials, and equal opportunity employment to all people without regard to race, color, national origin, religion, sex, age, veteran status, or disability.

This document is author-produced (unedited).

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