From the Archives
of the Rare Fruit Council of Australia
by Mark Wheatley
Star Apple Culture
Scientific name: Chrysophyllum cainito
Family: Sapotaceae
The
Star Apple is a member of the Sapotaceae family and its relatives
include the Mamey Sapote, the Abiu and the Sapodilla. It is indigenous
to the West Indies and Central America. It has since been introduced to
most other tropical regions of the world.
The tree is
distinguished by its dense foliage of oval, glossy, dark green leaves
with a coppery golden-coloured underside. The attractiveness of the
tree would justify its planting for its ornamental value alone.
The
Star Apple derives its name from the star-shaped section of the central
core evident when the fruit is cut transversely. There are two types of
Star Apple, the green and the purple, differing slightly in flavour;
the green often found to be slightly sweeter. The fruit is generally
spherical or slightly pear-shaped, between 5 to 10 cm in diameter,
containing a sweet, soft, juicy white flesh in which are embedded up to
10 glossy dark seeds. The fruit has a negligible acid content and must
be picked ripe, or the fruit will be bland in flavour and contain an
unpleasant tasting, viscous latex.
The small, purplish-white
flowers are borne in axillary umbellate clusters scattered along mature
twigs and partly concealed by the foliage.
The Star Apple is
tolerant of a wide range of soil types, growing well in heavy clay loam
and in sandy soils with sufficient supplementary irrigation and
fertilizer. It is a tree most suited to the lowland tropics, even
though it has performed quite well in certain regions of the Tableland,
i.e. Kuranda and Julatten. It is susceptible to death or injury by
frost, especially in its first years of growth. For the production of
fruit of good size and quality, provision should be made to supply the
trees with ample water, especially after the fruit has set. The trees
suffer large transpiration losses in hot dry weather because of the
Star Apple's dense foliage.
Many seedlings were planted in the
late 70s and early 80s, with some nurseries advising that plantings of
seedlings would be commercially viable. The large variation in size,
thickness of skin, number of seeds, yields per tree, time taken to bear
and the wide variation in appearance of fruit off different trees, has
meant only limited returns for growers and a luke warm reaction from
southern markets. One positive aspect concerning the large number of
Star Apple seedlings growing in North Queensland is the distinct
possibility of some very promising trees arising from this population.
Commercial plantings of propagated varieties have proved to be much more economic.
I
will now discuss the development history of our Star Apple orchard, and
reveal more specific information in relation to establishment and
management of the orchard and some advice on quality control.
The
land I have utilised for my orchard had previously grown sugar cane for
at least 60 years. Soil tests had revealed a very high acidity (4.2)
and a low organic matter content. The soil acidity was caused by
applications of chemical fertilizers over a long period of time with
insufficient applications of dolomite or lime to redress the balance.
The
yearly cultivation had lead to continual oxidisation of the little
organic matter in the soil leading to organic matter readings as low as
0.1%. To put this in perspective, virgin soil of this type has an
organic content of 5 to 6% roughly. The only element found in adequate
levels was phosphorus, of which there were very high levels, the reason
for this being that the high soil acidity kept the phosphates locked up
in the soil and unavailable for the cane to take up. So, applications
of superphosphate only added to this stock. I decided the most
cost-effective method of providing the trees with a fertile and
good-structured soil to grow in was to improve on each planting site
with the balance of the paddock improving slowly under fallow. The fact
that the soil was not being cultivated automatically reduced soil
erosion and leaching, and the mowed grass sod meant a steadily
increasing amount of organic matter in the soil. The pH is also rising
slowly, having risen from 4.2 to 5.5 over the last 9 years. I should
mention why I chose the Star Apple when in other tropical regions of
the world it has little economic importance.
We began our first
plantings of exotic fruit trees in 1979. We didn't initially plant many
of any one species because we decided to monitor the progress of these
for a couple of years and then decide on selecting several species that
would be most suitable for commercial production of fruit for our
particular climate and soil. The factors taken into consideration were
vigour, susceptibility to pests and diseases, time lag before
production, anticipated market acceptance of the fruit, and the final,
most limiting factor of those earlier years, the availability of
propagated trees of the most promising varieties of our selected
species. At this time the availability of grafted exotic fruit trees
was very limited, so we realised that we would have to propagate our
own trees. My good friend, Alan Carle, brought to my attention an
article on the propagation of Star Apples by tip cuttings under
intermittent mist and bottom heat. He also informed me he had quite an
advanced "Haitian" Star Apple marcot which he had imported from
Florida, and he did not mind if I took cuttings off this tree for our
own attempt at striking Star Apple cuttings. I had not even tried the
fruit at this stage but I had been told the purple Star Apple was an
attractive fruit and most people found them delicious for eating out of
hand.
We were all impressed with the great vigour of the
seedlings we were growing. The hothouse we constructed was a
conventional galvanised iron pipe igloo covered with white plastic.
Beds were constructed and misters, electronic timer, heating cable and
a thermostat were installed. Tip cuttings were prepared by cutting off
mature branch tips about 20 cm long, cutting off the bottom leaves,
cutting the rest in half, then scraping a 2 cm length of bark off the
end of the cutting, dipping the end in hormone powder, then placing
this end about 5 cm deep in a 50/50 sand, vermiculite mix under
10-minute intermittent mist. Callousing was evident in 4 weeks, and
within 8 weeks 80% of the cuttings were alive and had generated enough
root growth to be potted up and placed under 80% shade and intermittent
sprinkling every 30 minutes. Here they remained for about a month until
they established themselves and put out new growth.
The first 50
cuttings were grown on for about 12 months. They were then established
enough to be planted out in full sun and were about a metre high.
They
were planted out in December, 1982. Planting holes were dug with a .75m
diameter, tractor-mounted post hole digger. The holes (about a metre
deep) were half-filled with filter mud and about 10 kg of dolomite. The
auger was then used to mix the soil and filter mud. The trees were then
planted at each site about 20 cm above ground level to allow for
sinkage. The trees were then top-dressed with a compost that was made
by mixing chicken manure, filter mud, dolomite and bagasse with a front
loader and letting this break down for at least two months. The compost
was turned over every 2 weeks for aeration; the micro-organisms that
complete the composting process need oxygen as well as nitrogen and
organic matter. If the composting process is carried out properly,
these micro-organisms will actually fix nitrogen from the air in the
final stages of the composting process.
The trees were also
staked and given protection from the wind for about 6 months. Over the
next 2 years another 200 "Haitian" Star Apples were established in a
similar manner as the first 50. Irrigation was laid before the trees
were planted out. The trees were also mulched with hay to control the
vigorous weed growth.
The first fruit set in 2½ years
from planting out. The 1988 season was the first year all 250 trees
bore fruit. The total yield was approximately 7,000 kg harvested
between June and December, the most productive month being October.
Pests
and diseases: The major pest is fruit fly, and from September become a
serious problem if steps are not taken to reduce the population. We
have been using Diptrex, a spray that is of a low toxicity, breaks down
quickly in the environment, has a short withholding period and is very
effective against flies if the trees are sprayed twice a week.
We
also suffer small losses from birds, bats and rats. There is also a
mite that attacks new growing tips and disfigures affected fruit by
leaving them covered with scruffy brown patches. This mite is easily
controlled by a wettable sulphur spray once every 10 days till brought
under control.
The Star Apple trees get fertilized heavily with
filter mud after the season, and every two months from June till
December with a dressing of about 5 kg per tree of organo-fruit (GF)
and 1 kg of muriate of potash.
The fruit is quite slow to pick,
as each fruit has to be examined from above to ensure it has only a
very small ring of green (about as big as your thumb nail) around the
stem. Any greener than this and the Star Apple would contain
unacceptable levels of latex and be lacking in flavour. They have also
to be handled with care to avoid bruising. Bruising, surprisingly
enough, does not seem to initiate fruit breakdown like we see for
example in pears, but the consumers in southern markets will not buy
the Star Apple if it is soft.
The Star Apples are air-freighted
to Sydney, Melbourne and Brisbane. The Star Apple has a shelf life of a
week before the fruit begins to wrinkle and dry out. The fruit has an
attractive gloss for about 3 days after it is picked.
The fruit
is packed in mango-style trays with green plastic inserts to hold the
fruit. The average net weight of a tray is about 4.5 kg.
The
fruit count per box is between 28 and 10. Prices per tray ranged from
$30 per tray for large fruit first on the market in June, down to $12 a
box for late-season fruit of small size. I would estimate that we would
have averaged about $18 a tray after deductions for air freight. We
were happy with the prices we received, but thought we well deserved
it, as so much time was put into sorting and packing with every fruit
hand polished and carefully examined for insect damage or blemishes,
and any fruit not up to our high standard was rejected.
Quality
control is extremely important if you hope to maintain good prices. You
just have to have the customer satisfied and coming back for repeat
purchases to maintain a strong demand for your produce.
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