BLUEBERRY PRODUCTION (Continued from previous newsletter)
Excessive N should be avoided as berry production can be reduced. United States data show that leaf levels of N above 2.1 per cent of dry weight will reduce production. Balance the amount of N fertilizer against the number and length of fruiting shoots and new canes growing from the crowns. The greatest demand for N is when fruit is maturing and when shoot growth and floral initiation is occurring. If N is low, flower bud development for next year's crop will be reduced.
PHOSPHORUS (P) and POTASSIUM (K)
If soil tests and leaf analysis indicate P and K are deficient, readymix fertilizers such as 10:10:10 (N:P:K) should be applied each spring.
Soils containing 10 ppm or more of P do not require any more but should be monitored annually. Soils deficient in P(0-6 ppm) require 15 to 44 kg P per hectare (equivalent to 161 to 473 kg superphosphate). Soils with high exchange capacity do not require K if tests values are in excess of 90 ppm. For low reserve soils, deficiency levels exist at 150 ppm. Application of K will range from 28 to 84 kg per hectare or 61 to 182 kg potassium sulphate.
Both P and K can be applied together in the ready-mixed fertilizer described above. If K is not needed. a 16:20:0 mix will suffice. There are many combinations and it is advisable to consult your local Department of Agriculture advisory officer for your particular needs.
CALCIUM (Ca) AND MAGNESIUM (Mg)
Soil test values of less than 1.5 millliequivalents Ca and 0.25 milliequivalents Mg indicate a need for these elements. If both Ca and Mg are needed on mineral soils and the pH is 4.0 or less, apply dolomite (calcium magnesium carbonate) at 500 kg/ha and retest before further applications. If Ca alone is required and the pH is above 5.0 apply gypsum (calcium sulphate) at 500 kg/ha and retest in a few weeks. If Mg alone is needed, apply up to 500 kg epsom salts (magnesium sulphate) per hectare.
A soil test every 3 to 5 years should be made to ensure the balance between Ca, Mg and K is satisfactory. A ratio of Mg to Ca of 1.10 and K to Ca of 1.5 is suggested in some literature but this may vary according to local conditions.
|Age of plants |
|Amount of nitrogen |
to apply per plant (g)!
|Total Kg N/ha per year|
|8 or more||22||17-22||11-17||120-146|
*Rates are for mineral soils. On organic soils, normally only the Sep/Oct application is necessary.
In general terms, 1-year-old plants should receive about 50 g of a general 10:10:10:5 (N:P:K:Mg) fertilizer in spring. This amount should be doubled annually until year 6. Additional N or other elements can be applied as indicated by foliage symptoms and leaf analysis.
The fertilizer should be well-distributed around the base of the plant and watered in. Growers with microdrip or microjet irrigation systems may wish to inject the fertilizers through the system to simplify application. A guide to fertilizer application based on leaf analysis (Table 5) developed for highbush cultivars is useful for Australian conditions but may be subject to modification. Leaf samples should be picked when nutrient levels vary the least - probably mid-December in Australia. Leaves (5 from each of 10 bushes) should be picked from the fruiting shoots. Select the youngest full-sized leaves - fourth to sixth nodes from the tip.
Blueberry plants have shallow, fibrous roots and short periods of drought will adversely affect growth and production. Peak water demand occurs during the periods of fruit set and fruit growth. Inadequate watering in the final 2 to 3 weeks of fruit growth can seriously reduce berry size. Another critical period is February and March, when floral initiation for the following crop is taking place.
Inadequate irrigation in heat wave conditions will result in wilting and dieback of tender shoots and shrivelling of berries which then drop. Temperatures in excess of 45°C can be tolerated, provided there is adequate water. A rule of thumb guide for watering is to allow for 25 mm per week during the growing season with bursts of up to 38 or 40 mm in the final 2 to 3 weeks of fruit growth. Minimal watering is required in winter and natural rainfall should suffice. A mature plant requiring this amount of water would use 100 to 150 L of water a week. This is best supplied in small amounts on a regular basis. Overwatering that leads to waterlogged soils creates unfavourable conditions for growth and predisposes the roots to attack by root rot organisms, particularly Phytophthora species. Good quality water is essential. Blueberry plants are not salt-tolerant. A water test is essential to be certain salt levels are below 300 ppm (0.46 mS/cm).
Where water supply may be limiting, storage facilities are necessary and a minimum capacity should be 2.2 ML/ha. This will supply sufficient water for approximately 12 rain-free weeks.
Studies in the United States have clearly demonstrated the value of bee hives in the plantation to improve fruit set. Three or four hives per hectare should be adequate. Highbush cultivars, while self-fruitful, will respond to cross-pollination and should be planted in blocks of single cultivars. Rabbiteye cultivars require cross-pollination for successful fruit set. Ratios of 1:1 through to 1:5 of cross-pollinating cultivars are required.
Pruning is essential to promote strong new wood, increase plant size and maintain high yields with large berries. Poorly pruned or neglected bushes become crowded with weak, twiggy growth, produce small berries and fail to develop strong new wood for future production. Pruning is traditionally practised in late winter although plants can be pruned at any time from the end of harvest. During the first 2 to 3 years, pruning is limited to the removal of older twiggy growth at the base of the plant and those low branches that are likely to allow the fruit to lie on the ground. The strong new growth is left. The removal of flowers from 1-year-old plants will encourage vegetative growth and generate larger bushes in year two.
Mature plants are pruned to remove old canes that have no strong new wood, and week twiggy growth. It is important to prune systematically to make the job easier and to be sure that production is not lost. First year canes are not branched and will not produce much fruit in the coming season, but they are very important for subsequent crops. Fruit is mostly borne on strong laterals and twigs of second and third year canes. Fourth year and older wood is not very productive and should be removed. Cut canes back to the ground or a strong new side shoot. By removing one or two old canes and allowing these to be replaced each year, no canes will be over 6 years old.
A guide to pruning is as follows:
(1) Remove any canes damaged by disease, insects or mechanical injury.
(2) Cut out one or two older canes. Choose the least vigorous.
(3) Remove low branches and short, soft new shoots that develop from the crown late in the season.
(4) Remove weak, twiggy wood from the top and outer parts of the plant. Be sure sufficient light can penetrate to the centre of the plant. Weak, twiggy wood produces few flower buds and the berries are small.
(5) If the plants tend to overbear, tip back the fruiting shoots to remove about one third of the flower buds. These are the fat buds on the terminals of the previous season's growth.
Weed Control: Because of the multiple stems that develop from blueberry plant crowns, problem weeds can become entangled and difficult to remove. It is therefore very important to prepare the ground carefully before planting to ensure total weed control. In the first year, herbicide treatment must be done with caution because the root systems of young plants are near the surface and easily injured. It is preferable to delay using herbicides for at least 6 months.
Herbicides provide selective control of many annual and perennial weeds in established plantings and several safe and effective herbicides are registered in the United States for use in blueberry fields. Consult your local Department of Agriculture advisory officer for the choice of herbicides in your district.
Mulching with sawdust will assist weed control whilst preserving soil moisture.
|Manganese(Mn)||23 ppm||50 ppm||350 ppm||450 ppm|
|Iron(Fe)||60 ppm||60 ppm||200 ppm||400 ppm|
|Zinc(Zn)||8 ppm||8 ppm||30 ppm||80 ppm|
|Copper (Cu)||5 ppm||5 ppm||20 ppm||100 ppm|
|Boron(B)||20 ppm||30 ppm||70 ppm||200 ppm|
Source: C.C. Doughty, E.B. Adams and L.W. Martin, Highbush Blueberry Production in Washington and Oregon. Washington State University (1981)
There is no list of blueberry diseases in Australia due to the lack of commercial crop experience. A wide range of fungal and viral diseases have been reported in other countries but, to date, most of these have not proved troublesome in Australia.
Diseases or potential diseases recorded at Gosford include:
Botrytis twig and blossom blight Phomopsis species in 2-year-old canes;
Guignardia species associated with tip dieback and stem browning;
Botryosphaeria species associated with canker in the United States but no pathogenicity tests made in Australia;
Phytophthora species causing root rot.
There are control measures available for most disease problems and these can be discussed with your Department of Agriculture advisory officer.
A similar situation exists with insect pests as that described for plant diseases. Those observed in New South Wales include:
Queensland fruit fly has not proved to be a pest, despite large fruit numbers when fly populaions were locally high.
Nematodes recorded as pests in the United States include:
Birds can take up to 100 per cent of the crop. Many species of birds feed on blueberries in the United States, but experience in Australia is limited. At Gosford, starlings, silver-eyes, finches and the bul-bul have been observed feedfng on the fruit. All but the bul-bul were successfully repelled using methiocarb (Mesurol®), an emetic which discourages the birds from feeding on the fruit.
These sprays need to be applied every 7 to 10 days from first fruit colour until completion of harvest. Bird-scaring devices are many and varied, but need to be carefully assessed before use. These are probably the cheapest form of control but to be effective, must control birds the entire time fruit is on the bushes.
Anti-bird netting is probably the only sure way of achieving full control. This is the most expensive method but the gain in productivity and quality would off-set the cost in one or two years. It should be noted that netting will preclude the use of mechanical harvesters and restrict the operation to hand-harvesting with harvesting aids. Netting is very light and requires little support. A plantation can be enclosed at a cost of approximately $2 to $3 a bush, depending upon the price and quality of netting. Individual rows may be covered in tent fashion for about $1.50 a bush but vigorous plants will soon entangle the net. The netting should be installed when the first berries colour and removed after harvesting is completed. It should be stored in the dark for the rest of the year to prevent deterioration. The advantage of covering individual rows is that the same netting can be used for early and late cultivars, resulting in a significant cost saving.
Harvesting blueberries by hand is still the best method for collecting top-quality berries for the fresh market. It is an intensive operation involving continuous hand-eye co-ordination. A few simple rules which can increase the picking rate are:
1. Tie or strap a collecting bucket around the waist.
2. Pick with both hands turned upwards and gently massage the bunches. The ripe berries are easily removed. In most cases berries turn blue about a week before they are fully ripe. Do not attempt to remove all of the blue fruit - just those that come away easily.
3. While transferring fruit to the container your eyes should be selecting the next bunch. This way, no time is lost looking for fruit.
By picking this way, preferably in the cool of the day, it is not difficult for one picker to remove 10 kg an hour. In the United States trained pickers can remove 100 to 130 kg a day. The rate of picking is slower on young bushes and on those in which the fruit ripens over a long period of time. On most cultivars an interval of 7 to 10 days between harvests is acceptable and most fruit will be removed in about four pickings. On mature bushes and particularly those that have concentrated ripening, the rate, of hand-picking can be very high.
The labour required to hand-harvest one hectare will vary according to the cultivars planted. If only one cultivar is planted and each bush has 5 kg of berries to be harvested in four picks over 4 weeks then each bush, on average, will yield 1.2 kg. per pick. With 2,400 plants per hectare each harvest week will produce 2,880 kg. This can be removed over a 5 or 6-day period requiring up to 580 kg. to be removed each day. At this removal rate, ten or eleven people are required in the field 4 days a week for 4 weeks.
By shaking the berries into a catching frame, such as that used in the United States but perhaps modified for use in Australia, the removal rate can be as high as 350 kg per operator per day. On this basis, only two operators, instead of ten or eleven would be needed. An extra field hand or two would be necessary to assist with the catching frames as would additional fruit sorters to remove the small amount of unripe fruit, leaves and small twigs that would also be collected.
The labour requirement may also be reduced by planting cultivars that ripen over an extended period. Early, mid-season and late cultivars would extend the harvest from 4 to about 12 weeks with only one third as much fruit being picked weekly. This would mean approximately 190 kg per day per 5-day week over 12 weeks and this could be achieved by three or four hand pickers or one person with a catching frame.
Mechanical harvesters are used in the United States for farms over 10 hectares. These machines cost about US$80,000 and remove fruit at rates up to 1,800 kg. an hour. The fruit loss can be as high as 30 per cent and the fruit is generally only suitable for processing, although improvements, in the technology of mechanical harvesting are improving fruit quality and some United States blueberry farmers are successfully harvesting fruit for the fresh market with the new generation of harvesting machines.
Harvested fruit should be quickly removed from the field, sorted, packed and held in cool storage. Cooling to 12°C is sufficient. Longer shelf life is achieved if the fruit is held at 1°C to 2°C. The fruit is packed in 250 g punnets sealed with cellophane covers and packed in 12 or 20-punnet cartons for shipment to market. Freshly harvested fruit may be placed directly into plastic bags and frozen for later use in cooking.
Blueberries are a new fruit to most Australians and to capture a significant market it is essential that only good quality, fully-ripe berries are marketed. Immature blueberries are very tart - something like a lemon. Supply only the best and the market will grow.
Growers have a number of marketing options for fresh blueberries:
The Australian Blueberry Growers' Association (ABGA) is establishing a national marketing strategy. Only through industry unity and professional marketing on a national scale can growers expect to maintain good prices for their crop. Information concerning membership of the ABGA may be obtained by writing to ABGA, 2 Kembla St., Hawthorn, Victoria, 3122.
Because of the many factors that affect yield, the productivity of any cultivar cannot be precisely stated. However, as a general rule the yield in the second year from planting will be in the order of 1 kg. per bush. This should increase by 1 kg. per year to 5 kg. per bush in the seventh year. Production figures in the United States vary widely but yields of 10 kg. per bush are achieved on some cultivars. At the Gosford Horticultural Research Station, yields from third year plants have been as high as 8 kg per bush. Berry size is important for both harvesting and marketing. Large berries are quicker and easier to harvest and are certainly more marketable. Grading regulations set down by the Michigan Blueberry Growers' Co-operative prohibit the packaging of berries smaller than 1.3g for their premier label and 0.9g for their second grade.
Berry size of recognized cultivars is influenced largely by plant vigour, pruning and irrigation. Total yield is a function of overall management and climatic influences.
DATE: March 1985
* * * * * * * * * * * * *