Blueberries are native North American fruits. Each year in the U.S.A. up to 23 million kg. are harvested from wild plants, about one-third of the annual blueberry harvest. The commercial blueberry industry in North America began from selections of wild plants of the highbush species - Vaccinium corymbosum and V. australe made by F.C. Coville in 1909. Since then, breeding and selection have produced a wide range of highbush cultivars suited to regions with typically cold winters. The rabbiteye blueberry, V. ashei, is native to the warmer southern States (Florida, Georgia, Alabama) and commercial cultivars have been bred and selected to suit regions where winters are milder. A third group of cultivars are tetraploid hybrids derived from the above species, and these are also suited to the warmer climatic regions. Total U.S.A. blueberry production in 1981 was approximately 72 million kg., the main producing State being Michigan (22 million kg). There are over 13,000 ha planted to blueberries and new plantings totalling 5,000 to 6,000 ha are being established.
New Zealand exports the majority of its blueberries. Exports in 1979-80 were 8.5 tonnes, in 1981- 82, 33t and in 1982-83, 74 t. On the basis of known plantings, 1987 production will reach 1,500 tonnes. At present, 63 per cent of the crop goes to the United States, 20 per cent to Europe, 12.5. per cent to Australia and the remainder to Canada and Japan.
Data from the North American Blueberry Council indicate that United States annual per capita blueberry consumption is 330 g. By projecting this figure to Australia, our total annual consumption wuld be 4,500 t. At an average yield of 8 t/ha this amount could in theory be produced on 562 ha. However, production will depend mainly on the strength of promotional and marketing schemes. A strong export market should support more producing areas.
Blueberries may be marketed fresh, processed and frozen. Table 1 shows the average nutritional value of blueberry fruit.
|Food energy kJ||259.8||Ca, mg||15.0|
|Protein, g||0.7||P, mg||13.0|
|Fat, g||0.5||K, mg||81.0|
|Solids, %||15.3||Fe, mg||1.0|
|Carbohydrate,tota1 g||15.3||Na, mg||1.0|
|Pentosans, %||0.98||Vitamin A, IU||100|
|Fibre, g||1.5||Thiamine, mg||0.03|
|Invert sugar, %||4.89||Riboflavin, mg||0.06|
|Ash, g||0.3||Niacin, mg||0.05|
|Ascorbic Acid (Vitamin C) mg||15.0|
|Acids (as citric), %||0.93|
|Source: B.K. Watt and A.L. Merrill, Composition of Foods. United States|
Department of Agriculture, Agriculture Handbook 8 (1964).
For normal flower and fruit development, blueberry plants require winter chilling, the amount depending on the cultivar. Chilling models are used to determine accurately the number of chilling hours accumulated over the winter period. The model widely adopted for highbush cultivars is that devised by E.A. Richardson, S.E. Seeley and D.R. Walker*. For rabbiteye cultivars, the R.H. Biggs+ model may be used. Selected temperatures are converted to positive or negative chill units as follows:
and Walker °C
Units are computed daily for the full 24 hours and are accumulated over the winter period. Accumulation of positive units usually begins in autumn and ceases in early spring. Blueberry cultivars were originally categorized by their chilling requirements in terms of number of hours 7.2 °C. This is a much simplified model and often inaccurate. However, the chill requirement of a cultivar expressed as hours below 7.2 °C can approximately be equated to chill hours accumulated using the above models.
In general, the highbush cultivars require in excess of 800 chilling hours, rabbiteye from 350 to 650 and tetraploid hybrids from 250 to 400.
Thermograph data are needed to compute chilling units accurately but estimates can be made from daily maximum and minimum temperatures. Long-term records indicate extremes, which are useful in assessing variability. To avoid chilling problems that would cause serious economic losses, do not plant highbush cultivars where the chilling is below 800 hours for more than one year in ten. The same principle applies to other cultivars, each with specific chilling requirements. There is a danger in planting cultivars with low chilling requirements in cold areas. In these areas the chilling units required to initiate flower and leaf development are accumulated by mid-winter and if there is a short period of warm weather, plants are likely to break dormancy when the risk of frost is still high. In addition, the cold conditions are not ideal for fruit development. Local knowledge and experience are desirable before selecting cultivars where performance may be affected by local climatic conditions.
* "A model for estimating the completion of rest for 'Redhaven' and 'Elberta' peach trees", Hortscience 9, 331-332(1974).
+ Fruit Notes Newsletter No.8 (17th January, 1975), University of Florida, Gainesville.
|Cultivar Group||Chill units|
|Suitable climatic locations|
|>800||Tasmania, Sth.Australia, SW Western Australia,Victoria, central highlands|
of N.S.W., Queensland, and parts of coastal ranges of N.S.W.
|350-650||Victoria, Sth.Australia, Western Australia, central highlands of N.S.W.|
and Queensland, N.S.W. coastal ranges and plains.
|250-400||Coastal N.S.W. from approximately Sydney Basin northwards, southern|
Queensland, Atherton Tableland.
The preferred growing season is 160 frost-free days with at least 2 summer months with mean daily temperatures in excess of 20°C. Flower buds will tolerate temperatures to -3°C, but at full bloom, damage is likely at or below -2°C.
Once the climatic requirements are satisfied, the main criteria for assessing the suitability of an area for blueberry-growing are soil type, water, shelter and markets.
A well-drained acid soil (pH 4.2-5.2 for highbush and up to 5.5 for rabbiteye) is needed with organic matter content preferably above 5 per cent. Peat lands are ideal, provided drainage is adequate. Soil pH can be lowered using sulphur or aluminium sulphate, and raised with dolomite or lime (consult your local Department of Agriculture office regarding suitable rates for your particular soil type). Organic matter content is improved through cover cropping and the application of liberal dressings of mulch after planting.
The water table should be 25 to 70 cm below soil surface. The major blueberry soils in the United States are sands containing 3 to 5 per cent organic matter and with a high water table.
Blueberry plants have a shallow, fibrous root system and so require supplementary irrigation throughout the growing season. Mature bushes require the equivalent of 25 mm of rain per week for normal growth and as much as 38 mm during fruit development. Insufficient water during fruit growth, particularly in the last 2 weeks of ripening, will result in small berries. Water storage facilities or stream flow should provide up to 380,000 l/ha/week. Salt levels need to be less than 300 ppm(0.43 millimhos). Microjet and microdrip irrigation are the most efficient methods of providing the required quantities of water.
|Within row||Between Rows||Plants per Ha|
Dormant highbush blueberries are best planted in late winter or early spring before new growth begins. The top growth should be trimmed to balance the root system.
Containerized plants, particularly the low-chilling cultivars which do not become completely dormant, may be successfully planted at any time, but an early spring planting is preferable. This allows a full season's growth before the following winter. If the cultivar is vigorous, the fruit which may set the following season (first year) can be harvested in summer. On less vigorous plants, this early fruit should be removed to promote vegetative growth and the development of a strong bush before allowing it to crop.
If planting in summer, select cool cloudy days where possisble to reduce planting shock. Reduce the top growth if it is too vigorous.
Plant early in autumn so roots have time to establish before winter. This will ensure a rapid growth flush the following spring.
Set each plant at about the same depth as it was in the container. Spread the roots and fill in the soil around them to remove any air pockets which dry out the fine roots. Water immediately after planting, and in lighter soils mulch liberally with composted or aged sawdust, leaf mould, pine needles or similar materials. Black plastic mulch or weed matting are also successful.
As yet, local requirements are not well understood, and more research and commercial experience are needed. Overseas recommendations are of little help as they vary widely. However, soil analysis prior to planting will determine the basic requirements. Leaf analysis is a more precise guide to nutritional requirements. Blueberry plants use the three primary elements - nitrogen (N), phosphorus (P) and potassium (K) in larger quantities than the other elements. These elements require frequent replacement when large crops are regularly harvested.
Three secondary elements - calcium (Ca), magnesium (Mg), and sulphur (S) - are used in smaller amounts and may require periodic replacement in some soils.
Micronutrients are available in most soils and should only be supplied if specific foliar deficiency symptoms appear or a leaf analysis indicates a deficiency. Correction is usually by application of foliar sprays or injection through the irrigation system.
Newly-set plants are sensitive to fertilizer and the initial appliation should be delayed for 5 to 6 weeks after planting. Rabbiteye cultivars seem to require less fertilizer than highbush cultivars, but again, there is insufficient local information to accurately determine this.
Blueberry plants are particularly responsive to N. When sufficient is applied, the leaves are large, uniformly deep green and the growth vigorous. Deficiency symptoms are reduced size, pale leaf colour, weak or stunted growth and cessation of growth before the end of the season. Severe deficiencies will cause reddening of the foliage. Blueberry plants generally respond better when N is applied in ammonium form or as urea rather than with nitrate fertilizers. Fertilizers containing only nitrate N may cause root injury and possibly death.
The rate of application will depend upon plant symptoms and leaf analysis data. In general, newly-set plants require 10 to 12 g N in summer, preferably applied in split applications. The rates for 1-year-old plants is 10 to 14 g split into 3 applications in September, December and January. Table 4 suggests rates and timing of nitrogen application for highbush blueberries on mineral soils.
Exposure to hot drying winds may cause desiccation of young shoots, resulting in dieback and some times the shrivelling of developing fruits. This is most likely to occur when irrigation has been inadequate. The production of top-quality fruit depends largely on optimum moisture levels and minimal mechanical abrasion. Adequate shelter is essential and, if not available naturally, then windbreaks should be planned and planted well ahead of crop establishment. Consult your local Department of Agriculture office or the New South Wales Forestry Commission on suitable shelter trees for your area. Remember to irrigate and care for windbreak trees as you would any other crop.
Be sure to consider your marketing options before final selection of a growing area. Factors to consider are market locations (capital cities or local towns) and whether or not the fruit can be transported to these markets.
Blueberries planted on deep well-drained soils are the most productive. A deep loam or sandy loam with high organic matter is preferred. On poor sites growth is slow, plants are weak and production is low. Plantings on poorly-drained soils are less vigorous and may develop root problems.
Soil improvement is usually advisable. This allows for corrections of nutrient deficiencies, control of weeds and improvements in soil organic matter content and soil structure. Where land is under sod or pasture and not a potential source of weeds, there is little need to cultivate the whole site. Preparation of 2-m-wide strips with their centres spaced 3.0 m apart will suffice. This is achieved by pegging out the desired number of rows and spraying a 2-m-wide strip of herbicide along each row. An alternative is to cultivate the whole site to eradicate all vegetation before sowing the cover crop on a broad-acre basis. When the cover is dead, plough or rotavate the strip to prepare the ground for a cover crop. Topdress with fertilizer as required (a full soil analysis is recommended prior to ground preparation) and sow a green manure crop appropriate for the district. A suggested sequence is a summer crop of cowpeas, with or without sorghum, followed by a winter crop of oats and lupins. Always plough the crop in at the first sign of flowering. This will benefit the soil by building up organic matter and nitrogen. Following the final cover crop, allow the land to lie fallow, and observe weed growth. Apply herbicide 3 weeks prior to the final cultivation. Rotavate and hill the rows using an offset disc plough or similar implement. Hilling the rows ensures adequate drainage, particularly on flat land. The planting beds should be about 1m wide. This allows machinery access between the rows. The inter-row space is best left as grass sward which can be mown and the cuttings used as replacement mulch around the plants. About 6 weeks prior to planting, apply a liberal dressing of poultry manure, or barnyard manure, if available. Check the pH of the manure to ensure it is not likely to raise the soil pH. Install the irrigation system and make a final check on weeds before planting.
The distance between plants may be varied according to variety and location. Plants growing in sandy soils will produce larger bushes than those on heavier soils. Rabbiteye cultivars are generally more vigorous and spreading than highbush cultivars. Size can be controlled by pruning, but adequate spacing should be allowed for growth.
The most practical planting design will depend upon cultural practices and the method of harvesting. A spacing of 1.5m between plants appears to be most suitable for rabbiteye cultivars, down to 1.4m for highbush cultivars. An advantage of closer spacing is higher productivity in the earlier years, but with the risk of some crowding in the mature planting when each row develops into a hedgerow. Table 3 gives planting densities at different spacings.
Where harvesting will be by machine, the rows should be 3.0 to 3.3m apart and the plants closer together to allow a hedgerow formation. Allow a headland of 8m for turning large machinery.
DATE: January 1985
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