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*. |
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.
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