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.
DATE: May 1989
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