Bagging: Protect
Your Fruit
Scientific
Name: Mangifera
indica
Family:
Anacardiacea
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.
Table 1
Percentage
diseased mango fruits bagged with plastic bag, blue paper match and
newsprint
| Treatment |
Total
Number of Fruit |
Damage at
Harvest Time |
Damage 5 Days
after Harvest |
| Plastic
Bag |
150 |
24 |
48 |
| Blue
Paper Match |
150 |
5 |
12 |
| Newsprint |
150 |
10 |
18 |
| Control |
150 |
32 |
62 |
Table 2
Percent
insect damage of mango fruits wrapped with plastic bag, blue paper
match and newsprint
| Treatment |
Total Number
of Fruit |
Insect Damage |
Grade 1 Fruit |
Grade 2 Fruit |
| Plastic
Bag |
150 |
23 |
0 |
0 |
| Blue
Paper Match |
150 |
3 |
69 |
14 |
| Newsprint |
150 |
12 |
61 |
11 |
| Control |
150 |
65 |
0 |
0 |
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.
REFERENCES
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.
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