Christine Gray's excellent article "To Bag Or Not To Bag?" in the May, 1988 issue of the newsletter should prompt all fruit growers who are interested in producing a perfect, blemish-free fruit to investigate further.
In Japan where the average orchard is only two to three acres, bagging is an important cultural operation for fruits such as loquat, persimmon and nashi fruit (Asian pear). Johnson (1983) states that bagging is undertaken to reduce the number of pesticide applications and to improve fruit appearance. In some regions it provides a major defence against fruit piercing moths as there are no effective pesticides. With nashi fruit cultivars such as Nijisseiki and other clear skin cultivars, bagging makes possible the production of fruit of a very attractive blemish-free fruit with considerable eye appeal.
Bagging of Nijisseiki commences as early as two weeks after petal-fall, along with hard thinning and selection of appropriate fruits. Initially a semi-clear paraffin-coated bag, 6x5 cm in size is used. A skilled worker can apply 5,000 bags in a day. A second bagging is undertaken during early summer using a larger, more durable double-walled bag. Approximately 2,000 of these can be put in place during a day. During manufacture the bags are impregnated with low levels of pesticides.
Bagging of mango fruits is widely practiced in the Philippines. Fruits are individually wrapped with bags made from newspaper after the initial heavy fruit drop. Baggers climb bamboo scaffolds erected near, on or between trees, or, climb through the branches or up ladders to reach the fruit.
In Cebu, Ortega (1979) compared the efficiency of three different types of materials to be used as bags: perforated plastic bags, newsprint and blue paper match. She found that blue paper match and newspaper dramatically reduced the number of pest-damaged fruits and more than seventy percent of mangoes were in the grades one and two category (see Tables 1 and 2). Plastic bags significantly reduced insect attack but not the softening of fruit.
|Damage 5 Days|
|Blue Paper Match||150||5||12|
|Insect Damage||Grade 1 Fruit||Grade 2 Fruit|
|Blue Paper Match||150||3||69||14|
During a recent visit to Thailand, I observed a number of different types of fruit protected by newspaper and perforated plastic bags, producing perfect, blemish-free fruit. A forty-thousand-tree mango orchard near Chiang Mai, which exports fruit to Japan, employs three hundred people to bag fruit during the fruiting season. Bags are made of newspaper and the sides stapled together. These are replaced when they become damaged. Trees are spaced at a distance of 5x5 metres and pruned regularly so that fruit can be easily reached. Some of the new plantings are spaced at 1.5x1.5 metres. These are pruned heavily and produce a smaller number of fruit per tree compared to a tree in an orchard at the wider spacing, but, fruit size is significantly larger.
The covering of lychee fruit with paraffin-impregnated paper bags is a recommended cultural operation by the South African Department of Agriculture. This gives protection against the lychee moth, Argyroploce peltastica Meyr., for which chemical control has been unsuccessful, and several species of fruit bats.
The Egyptian fruit bat, Rousettus aegyptiacus, is the species most commonly found in lychee orchards. This bat occurs in Southern Africa, in the Nile Valley as far as Egypt, the Eastern Mediterranean area and Arabia. It is brown to grey-brown with dark, grey-black wings (wingspan up to 670 mm) and has a typical 'dog face'. These bats do not normally rest in trees during the day but sleep in caves.
De Villiers (1983) cites a study by Jacobsen of these animals. The bats leave the caves 20 to 40 minutes after sunset and within an hour of sunset most of them are out looking for wild fruit and lychees. They start returning to the caves from 02h00 and by 03h45 most of them have returned. A distance of 24 km from the lychee orchard to the cave was covered in 90 minutes, a speed of 16 km/h.
It has been established that this bat eats an average of eight lychees per night. It has also been found that they feed in an orchard for 5 to 6 hours and that a bat picks a lychee every half to three-quarters of an hour. From lychee residues under a tree it was determined that more than 2,000 bats visited a 300-tree orchard in a single night. If, therefore, 2,000 bats each eat eight lychees per night, this means that 16,000 fruit or about 53 boxes per night are eaten. This feeding rate gradually declines as the crop is harvested.
It was established that 61 boxes of fruit were 'picked' by bats in the 300-tree orchard during the first night, but by the seventh night this had dropped to 13 boxes. The total loss suffered by this orchardist during a single week was 204 boxes of lychees from 300 trees.
De Villiers (1983) mentions that several control methods were tested - electric lights, shooting, deterrent containing carbolineum, nets and sound imitations of predators such as owls. None of these were very successful. The only successful control measure is the use of lychee bags with which the bunches are covered after the November fruit drop, and they remain in position until harvested about six to eight weeks later.
Menzel and Simpson (1986) suggest that the only effective method to control flying foxes and birds is netting. The netting is expensive, up to $4,000 per hectare depending on the bird species that you wish to control and the expected net life is only 10 years. A number of lychee cultivars planted in orchards in different parts of Australia do not fruit regularly and heavily. The installation of netting may not be economically feasible in the long term. Bagging may be an alternative. Labour costs in large orchards would be very high, but, in smaller family-run orchards the labour would be time-intensive.
During a recent trip to Sydney and on a number of other occasions, I have observed a high percentage of brown-coloured and immature lychees being offered for sale at Flemington Wholesale Market and at retail outlets. It was obvious that growers had picked early, presumably to prevent loss of crop from flying foxes and not undertaken the correct post-harvest treatment of fruit. A visitor once commented on seeing fruit on my lychee tree, "Do you grow the red-skin types of lychee? All we get is the brown-skin types in Melbourne."
I have heard a story circulating that the post-harvest treatment developed by research personnel from the Queensland Department of Primary Industries, N. S. W. Department of Agriculture and the C.S.I.R.O., does not work. Of course it doesn't work if growers do not follow the procedure meticulously and correctly. Such an attitude can only lead to a reduction in buyer confidence and returns to the grower, as well as damage the infant lychee industry. Lychee growers should refer to the article by Brown and Watkins (1987) for correct post-harvest handling, cooling and marketing.
A desire to reduce pesticide applications as well as damage from flying foxes and birds, and, produce a blemish-free fruit, has led me to experiment with paraffin-impregnated paper bags on a range of fruits. This has been generally successful and has offered protection from both flying foxes and birds. Damage has been sustained from possums.
It is important that growers of rare fruit that are unknown to the buying public ensure that their product is well-presented. Shredded wood and paper used in the past for packing have been shown to carry spores that cause fruit rot. Plastic carton inserts are useful and fruit will not move and hence bruise during transport if fitted correctly. For example, yellow-skinned abius would present very well against the green background colour of a plastic insert. Professionally-prepared and coloured promotional material is essential to educate the consumer. Other forms of promotion are highly desirable.
Growers may wish to experiment with different types of bags and share their experiences. Perhaps they could also encourage research personnel to undertake some experimentation as well.
Brown, B.I. and Watkins, J.B., 1987. Lychee. Postharvest handling, cooling and marketing. Rare Fruit Council of Australia Inc. Newsletter No.47, 6/87
De Villiers, E.A. 1983. Farming in South Africa. Fruit Bats in litchis. Litchis H.4.
Johnson, J.F. 1983. A study of Asian Pears in Japan. 53 pp.
Menzel, C.M. and Simpson D.R., 1986. Conclusion - The Potential of Lychee in Australia. In "Proceedings of the First National Lychee Seminar", 143 pp.
Ortega, V.G., 1979. Bagging of Mango Fruits. Second Fruit Symposium. Cebu City. December 12-14, 1979.
DATE: November 1988
* * * * * * * * * * * * *