CARAMBOLA CULTURE
SCIENTIFIC NAME: Averrhoa carambola
FAMILY: Oxalidaceae
Industry Potential - Comment
Carambola has been grown in north Queensland for at least 100 years. More commonly known as the 'five corner', it has had little more value than a backyard tree - mostly favoured by children. A very small amount is marketed in north Queensland fruit shops, mainly for the tourist trade.
It is generally thought of as a second-rate fruit - which has been warranted because of the poor quality and variable nature of fruit produced.
However it is now obvious that clonal material recently introduced (and some yet to be brought in) is so superior that undoubtedly, in the years to come, selected grafted material will provide a new image and hopefully, a commercial industry will be established. There are no real problems with the productive capacity of trees, but the fruit fly and fruit sucking moth damage is a serious limiting factor. Whilst the Department is not promoting commercial planting, it is hoped that in the near future some superior cultivars will be recommended. The main objective should be to present the buying public with fruit of the best cultivars available in order to remove past prejudices and to make significant market impact.
If only for the local tourist market alone, there is very good market potential for good quality, pest-free fruit. Overseas the fruit is processed into juice, and in mainland China a particularly fine product is made from dried and sugared carambola.
Botany
An evergreen tree native to the Indo-Malayan region, tree habit is symmetrical, up to 12m in height. Leaves are compound with between 2 and 11 leaflets, each 20 to 90 mm long. The flowers are pink, perfect, 8 to 12 mm long and occur in auxiliary and terminal clusters. The fruit is a fleshy berry, 80 to 180 mm in length by 60 to 100 mm in diameter. The fruit is acutely 4- to 6-angled (but most commonly 5) and star-shaped in cross section. It can be green, yellowish-white, yellow or reddish in colour when ripe, according to cultivar. Seeds number 0 to 12, are light brown and up to 10 mm long.
Fruit Characteristics
Flesh characteristics range from soft to 'crunchy' - the latter more like the texture of an apple - as in the cultivars Wheeler and Fwang Tung - both of which can be eaten when they appear relatively green. Some cultivars appear very sweet, but Brix (total soluble solids and approximate figure for sugar content) levels are only in the order of 5 to 8, as compared with mango, which is 15 to 20. Oxalic acid content is high. A range of characteristics are:
| Oxalic acid (g/100 g juice) | 0.04 to 0.7 |
| Acidity (m.e.q./100 g juice) | 1.9 to 13.1 |
| pH | 2.4 to 5.0 |
| Brix | 5.0 to 10.0 |
| Total Sugars | 3.5 to 8.5% |
| Water content | 90% |
| Protein | 0.75% |
| Crude fibre | 0.7% |
| Vitamin A (I.U./100 g) | 560 |
| Vitamin C (m.g./100g) | 14 to 90 |
Some cultivars have a relatively good shelf life (eg. B1), whilst others quickly deteriorate (eg. Star King). They also vary in flesh firmness in relation to packing and transport.
There is some variation in susceptibility to fruit fly attack, but as yet, not documented.
Climatic Requirements
The carambola is well suited to frost-free areas of coastal Queensland below 300 m. The preferred growing and cropping area is north of Rockhampton, although in protected situations it will bear as far south as northern New South Wales.
However, in southern Queensland/northern New South Wales there is only one main cropping period, in February/March, whereas in northern Australia there is some fruiting throughout the year with usually a peak in June/August. Young trees are very susceptible to frost, but are more tolerant when advanced. Aspect is not important in the north, but northerly slopes are preferred in southern Queensland.
Soil and Drainage Requirements
The carambola is not fastidious and will perform well on a range of soil types from sands to heavy clay loams. However, it grows best on well-drained, deep clay loams. It is tolerant of a range of pH levels but pH 5.5 to 6.5 is preferred.
Planting sites should be well-drained, but as long as surface water is not ponded for any length of time, then few problems arise.
Cultivars
Taiwan, Malaysia, Thailand and Florida appear to have done the most work in carambola selection. Information from Taiwan and Thailand is relatively sparse in this text. Cultivar lists are as follows:
N.B. * = not yet introduced into Australia.
| Florida | Star King 'Sweetie'*, Key West*, Thai-Knight, Arkin, Fwang Tung, Hart, Maha, Mih Tao*, Newcomb*, Pei Sy Tao*, Tean Ma*, Wheeler, White*, Dah Pon* and Thayer*. |
| Indonesia | Kapuk*, Tinggo* and Demak*. |
| Malaysia | B1 (Yong Toh Yin), B2 (Maha 66), B3* (Foo Fatt), B4 (Sungei Besi 1), B5 (Sungei Besi 2), B6 (Sungei Besi 3) B7* (Sungei Besi 4), B6 (Sungei Besi 5), B9* (Lam May Yong), B10 (Chin Sing Keow), B11 (Chan Yong 1), B12* (Chan Yong 2), B13*, B14*, B15* and B16*. |
| Singapore | Leng Bak (Leng Baec) and Jurong. |
| Mainland China | Hong Hua*, Far Dee*. |
| Taiwan | Iu Tho, Mih Tao*. |
| Australia | Apart from recent introductions, the only locally-selected cultivars documented in north Queensland are Dallachy and K.H.R.S. Large Sour (the latter only suitable for processing). The introductions Fwang Tung and B16, whilst being very good fruit, are not properly authenticated. Many other countries in Asia and the Americas have carambola selections, but information is very limited. Fwang Tung is an excellent home garden variety, very sweet even in immature condition. However it has large thin wings and varieties such as Arkin may be more suitable for packaging and marketing commercially. |
Many of the more recently imported varieties have not yet been screened to identify their potential in Australia but this work should be substantially completed by 1985.
Flowering and Fruiting Characteristics
Grafted trees will commence bearing within nine months as from planting out, but if culture is good, there follows a major period of vegetative growth and substantial cropping commences in year two or three. Trees are relatively long-lived, and at 10 years of age may bear as high as 900 kg per year, particularly with large sour-fruited cultivars.
For superior cultivars, yields in north Queensland can be expected in the range of 100 to 300 kg per annum in years four to ten.
Flowers appear along the smaller branches, and depending on stamen position relative to the stigma, may be cross- or self-incompatible. However, obviously high-yielding cultivars are mainly self-pollinating, although insects may be required. From anthesis to fruit maturity is approximately 2½ to 3 months, but this is not well-documented, particularly for different cultivars.
In north Queensland, production peaks are in December/February and June/August, but vary according to climatic conditions and cultivars. There may be smaller crops throughout the year.
Crop Control
No studies have been conducted, but pruning, fertilizing and water availability all affect flowering flushes. It should be feasible to manipulate the cropping pattern, particularly for winter production when few other fruit are available. Stressing trees by withholding water in dry periods appears to be a useful method for inducing flower initiation.
Fertilizing
Recommendations vary from country to country, and obviously there is considerable latitude in rates and ratios of elements. However a suggested programme is 200 g of single super phosphate dug into the planting site.
Then in August, December and April each year, split dressings up to an annual total of 10 g N, 2 g P, and 17 g K per tree per year of age up to a maximum at 15 years. In August, 0.5 kg of Dolomite per tree per year of age up to a maximum at 10 years. All fertilizers and lime broadcast in a 1m band centred on the drip line.
Organic mulching with bagasse, peanut shell, straw, or like material is beneficial and should be applied in a 1.5 m band centred in the drip line to a depth of 75 to 150 mm each year for the first three years. If poultry or animal manure is supplied also, inorganic fertilizers should be reduced.
There appears to be little tendency for carambola to show trace element deficiencies on all but calcereous soils - but zinc should be watched in particular.
Weed Control
Contact weedicides - paraquat and/or glyphosate - are preferred to control the weed spectrum. Pre-emergent weedicides have not been studied.
Windbreaks
The carambola is fast growing and susceptible to limb breakage, particularly up to four years of age. Windbreaks are desirable to prevent fruit loss. Most fruit are dislodged in cyclonic winds and Star King cultivar in particular only requires relatively low wind velocity to lose the crop. Suitable wind-break species are Casuarinas, jambolan, (Syzygium cuminii), Leucaena leucocephyla, bamboos, and for the short term, bana grass. Carambola trees, however, should not be shaded.
Pruning
Pruning may be necessary to shape the tree and also to reduce limb breakage. It is also desirable to keep trees as compact as possible to facilitate harvesting.
Irrigation
The tree has a high water demand, and in times of water deficit irrigation rates should be at least 0.9 of pan evaporation (30 to 50 mm per week). However some stress will induce flowering.
Harvesting
Fruit must be detached by hand at the time of mature colouring (consistent with acceptable sweetness). Fruit of most cultivars are easily bruised and rough handling causes the wing edges to discolour rapidly. Fruit should be packed in single layers on shredded paper or like material in a tray pack. Pre-cooling and refrigeration (10 to 20°C) together with a PVC wrap, will give relatively good shelf life. No post-harvest chemical or hot water treatments appear to have been trialled.
Pests and Diseases
The fruit and tree is remarkable in that it has few problems with pests and diseases. Flying foxes are not a problem. The main concern is leaf roller caterpillars, and more particularly, fruit flies. In Asia, field sanitation (removing stung and fallen fruit) and bagging with paper or plastic bags is common, and the latter may be worth the effort in Australia, but only if market return is commensurate.
However, regular spraying of fruit with Fenthion (0.04%) or Dimethoate (0.03%) will control flies. In addition, Maldison 25 g (25% W.P.) plus Protein Hydrolysate 25 ml in 1 litre of water, painted on a few of the main tree limbs or trunk at weekly intervals will assist control.
Propagation
For commercial production, only planting of clonal material is recommended. Seed is difficult to extract from fruit, but best left to decompose and then crushed over a wire sieve together with running water. Sow seed immediately, but barely cover with medium. Seedling growth is rapid, and repotted plants can
be of suitable size (0.6 to 1m tall) in a few months.
Propagation can be carried out by side veneer graft, chipbudding, modified forkert budding, or wedge grafts.
Side veneer grafts are probably the most reliable. A defoliated, hardened (brown) scion piece with 5 to 6 nodes and of appropriate diameter (slightly thinner than the Graft area on the stock) is prepared and slotted in the normal way for a side veneer. The scion is tightly bound with PVC tape.
After 4 weeks, if the scion is still alive, the upper part of the tie is removed and the stock decapitated just above the graft. Watering should then be reduced to about one-third of normal requirements until the scion makes significant growth.
Top working can be carried out with side veneers, or cutting back and wedge or side veneer grafting new growths.
Alternatively, bark grafts (as per deciduous fruits) are successful on cut-back limb edges.
Air layering appears difficult with carambola, and particularly with some cultivars; similarly, cuttings are not reliable - even under mist.
Density and Planning
Carambola cultivars vary in growth rates, and permanent tree spacings range from 5 metres to 10 metres. However, double planting in the row and tree removal at a later date is possibly the most efficient land use. Planting sites do not require substantial pre-treatment, although deep ripping in hard-packed soils is beneficial. Poultry or animal manure or organic waste dug into the planting position some six months prior to field planting is recommended.
DATE: January 1983
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