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Tropical Plant "Papaya"
Carica papaya
The papaya, Carica papaya L., is a member of the small
family Caricaceae allied to the Passifloraceae. As a dual- or
multi-purpose, early-bearing, space-conserving, herbaceous crop,
it is widely acclaimed, despite its susceptibility to natural
enemies. In
some parts of the world, especially Australia and some islands
of the West Indies, it is known as papaw, or pawpaw, names
which are better limited to the very different, mainly wild
Asimina triloba Dunal, belonging to the Annonaceae.
While the name papaya is widely recognized, it has been corrupted
to kapaya, kepaya, lapaya or tapaya in southern
Asia and the East Indies. In French, it is papaye (the
fruit) and papayer (the plant), or sometimes figuier
des Iles. Spanish-speaking people employ the names melón
zapote, lechosa, payaya (fruit), papayo or papayero
(the plant), fruta bomba, mamón or mamona,
depending on the country. In Brazil, the usual name is mamao.
When first encountered by Europeans it was quite naturally
nicknamed "tree melon".
Papaya Description
Commonly
and erroneously referred to as a "tree", the plant is properly
a large herb growing at the rate of 6 to 10 ft (1.8-3 m) the
first year and reaching 20 or even 30 ft (6-9 m) in height,
with a hollow green or deep-purple stem becoming 12 to 16
in (30-40 cm) or more thick at the base and roughened by leaf
scars.
The
leaves emerge directly from the upper part of the stem in
a spiral on nearly horizontal petioles 1 to 3 1/2 ft (30-105
cm) long, hollow, succulent, green or more or less dark purple.
The blade, deeply divided into 5 to 9 main segments, each
irregularly subdivided, varies from 1 to 2 ft (30-60 cm) in
width and has prominent yellowish ribs and veins. The life
of a leaf is 4 to 6 months. Both the stem and leaves contain
copious white milky latex.
The
5-petalled flowers are fleshy, waxy and slightly fragrant.
Some plants bear only short-stalked pistillate (female) flowers,
waxy and ivory-white; or hermaprodite (perfect) flowers (having
female and male organs), ivory-white with bright-yellow anthers
and borne on short stalks; while others may bear only staminate
(male) flowers, clustered on panicles to 5 or 6 ft (1.5-1.8
m) long.
There
may even be monoecious plants having both male and female
flowers. Some plants at certain seasons produce short-stalked
male flowers, at other times perfect flowers. This change
of sex may occur temporarily during high temperatures in midsummer.
Some "all-male" plants occasionally bear, at the tip of the
spray, small flowers with perfect pistils and these produce
abnormally slender fruits. Male or hermaphrodite plants may
change completely to female plants after being beheaded.
Generally,
the fruit is melon-like, oval to nearly round, somewhat pyriform,
or elongated club-shaped, 6 to 20 in (15-50 cm) long and 4
to 8 in (10-20 cm) thick; weighing up to 20 lbs (9 kg). Semi-wild
(naturalized) plants bear miniature fruits 1 to 6 in (2.5-15
cm) long. The skin is waxy and thin but fairly tough.
When
the fruit is green and hard it is rich in white latex. As
it ripens, it becomes light- or deep-yellow externally and
the thick wall of succulent flesh becomes aromatic, yellow,
orange or various shades of salmon or red. It is then juicy,
sweetish and somewhat like a cantaloupe in flavor; in some
types quite musky. Attached lightly to the wall by soft, white,
fibrous tissue, are usually numerous small, black, ovoid,
corrugated, peppery seeds about 3/16 in (5 mm) long, each
coated with a transparent, gelatinous aril.
Papaya Origin
and Distribution
Though
the exact area of origin is unknown, the papaya is believed
native to tropical America, perhaps in southern Mexico and
neighboring Central America. It is recorded that seeds were
taken to Panama and then the Dominican Republic before 1525
and cultivation spread to warm elevations throughout South
and Central America, southern Mexico, the West Indies and
Bahamas, and to Bermuda in 1616. Spaniards carried seeds to
the Philippines about 1550 and the papaya traveled from there
to Malacca and India. Seeds were sent from India to Naples
in 1626.
Now
the papaya is familiar in nearly all tropical regions of the
Old World and the Pacific Islands and has become naturalized
in many areas. Seeds were probably brought to Florida from
the Bahamas. Up to about 1959, the papaya was commonly grown
in southern and central Florida in home gardens and on a small
commercial scale. Thereafter, natural enemies seriously reduced
the plantings.
There
was a similar decline in Puerto Rico about 10 years prior
to the setback of the industry in Florida. While isolated
plants and a few commercial plots may be fruitful and long-lived,
plants in some fields may reach 5 or 6 ft, yield one picking
of undersized and misshapen fruits and then are so affected
by virus and other diseases that they must be destroyed.
In
the 1950's an Italian entrepreneur, Albert Santo, imported
papayas into Miami by air from Santa Marta, Colombia, Puerto
Rico and Cuba for sale locally as well as shipping fresh to
New York, and he also processed quantities into juice or preserves
in his own Miami factory.
Since
there is no longer such importation, there is a severe shortage
of papayas in Florida. The influx of Latin American residents
has increased the demand and new growers are trying to fill
it with relatively virus-resistant strains selected by the
University of Florida Agricultural Research and Education
Center in Homestead.
Successful
commercial production today is primarily in Hawaii, tropical
Africa, the Philippines, India, Ceylon, Malaya and Australia,
apart from the widespread but smaller scale production in
South Africa, and Latin America.
Annual
papaya consumption in Hawaii is 15 lbs (6.8 kg) per capita,
yet 26 million lbs (11,838,700 kg) of fresh fruits were shipped
by air freight to mainland USA in 1974, mainly direct from
Hilo or via Honolulu.
Puerto
Rican production does not meet the local demand and fruits
are imported from the Dominican Republic for processing.
The
papaya is one of the leading fruits of southern Mexico and
40% of that country's crop is produced in the state of Veracruz
on 14,800 acres (6,000 ha) yielding 120,000 tons annually.
Fruits
from bisexual plants are usually cylindrical or pyriform with
small seed cavity and thick wall of firm flesh which stands
handling and shipping well. In contrast, fruits from female
flowers are nearly round or oval and thin-walled. In some
areas, bisexual types are in greatest demand. In South Africa,
round or oval papayas are preferred.
Papaya Varieties
Despite
the great variability in size, quality and other characteristics
of the papaya, there were few prominent, selected and named
cultivars before the introduction into Hawaii of the dioecious,
small-fruited papaya from Barbados in 1911. It was named 'Solo'
in 1919 and by 1936 was the only commercial papaya in
the islands. 'Solo' produces no male plants; just female (with
round, shallowly furrowed fruits) and bisexual (with pear-shaped
fruits) in equal proportions. The fruits weigh 1.1 to 2.2
lbs (1/2-1 kg) and are of excellent quality. When the fruit
is fully ripe the thin skin is orange-yellow and the flesh
golden-orange and very sweet.
'Kapoho
Solo' or 'Puna Solo' was discovered and became popular
with growers on Kauai before 1950. In 1955 a 'Dwarf Solo'
(a back-cross of Florida's 'Betty' and 'Solo') was introduced
to aid harvesting, and this became the leading commercial
papaya on the island of Oahu. It was, up to 1974, the only
export cultivar. It is pear-shaped, 14 to 28 oz (400-800 g)
in weight in high rainfall areas, and has yellow skin and
pale-orange flesh.
Papaya 'Waimanalo'
(formerly 'Solo' Line 77) was selected in 1960 and released
by the Hawaii Agricultural Experiment Station in 1968 and
soon superseded Line 8 'Solo' on Oahu for the fresh fruit
market because of its firmness and quality, but there it is
usually too large for export. It has long storage life and
is recommended for sale fresh and for processing. Since 1974
this cultivar has been produced commercially on the low-rainfall
island of Maui where it ripens at a greener color than on
the island of Hawaii and is exported to cities in the northwestern
and central USA. The growers raised only bisexual plants;
they say that the fruits of female plants are too rough in
appearance.
Papaya 'Higgins'
(formerly Line 17A), the result of crosses in 1960, was introduced
to Hawaiian growers in 1974. It is of high quality, pear-shaped,
with orange-yellow skin, deep-yellow flesh, and averages 1
lb (0.45 kg) when grown under irrigation. In and territory
or seasons of low rainfall, the fruit is undersized.
Papaya 'Sunrise
Solo' (formerly HAES 63-22) was introduced from Hawaii
into Puerto Rico. The fruit has pink flesh with high total
solid content. In Puerto Rican trials, seeds were planted
in mid-November, seedlings were transplanted to the field
2 months later, flowering occurred in April and mature fruits
were harvested from early August to January. Recent selections
from Puerto Rican breeding programs are 'P.R. 6-65' (early),
'P.R. 7-65' (late), and 'P.R. 8-65'.
Venezuelan
papayas are usually long and large, ranging in weight from
2 to 13 lbs (1-6 kg) and mostly for domestic consumption or
shipment by boat to nearby islands.
Papaya Pollination
If
a papaya plant is inadequately pollinated, it will bear a
light crop of fruits lacking uniformity in size and shape.
Therefore, hand-pollination is advisable in commercial plantations
that are not entirely bisexual.
Bags
are tied over bisexual blossoms for several days to assure
that they are self-pollinated. The progeny of self-pollinated
bisexual flowers are 67% bisexual, the rest being female.
To
cross-pollinate, one or 2 stamens from a bisexual flower are
placed on the pistil of a female flower about to open and
a bag is tied over the flower for a few days. Most of such
cross-pollinated blooms should set fruit. Resulting seeds
will produce 1/2 female and 1/2 bisexual plants.
By
another method, all but the apical female flower bud are removed
from a stalk and the apical bud is bagged 1-2 days before
opening. At full opening, the stigma is dusted with pollen
from a selected male bloom and the bag quickly resealed and
it remains so for 7 days.
Plants
from female flowers crossed with male flowers are 50-50 male
and female. Bisexual flowers pollinated by males give rise
to 1/3 female, 1/3 bisexual and 1/3 male plants.
South
African growers have long been urged to practice hand-pollination
in order to maintain a selected strain and, in breeding, to
incorporate factors such as purple stem, yellow flowers and
reddish flesh so that the improved selection will be distinguishable
from ordinary strains with non-purple stems, white flowers
and yellow flesh.
Papaya Climate
The
papaya is a tropical and near-tropical species, very sensitive
to frost and limited to the region between 32º north and 32º
south of the Equator. It needs plentiful rainfall or irrigation
but must have good drainage. Flooding for 48 hours is fatal.
Brief exposure to 32º F (-0.56º C) is damaging; prolonged
cold without overhead sprinkling will kill the plants.
Papaya Soil
While
doing best in light, porous soils rich in organic matter,
the plant will grow in scarified limestone, marl, or various
other soils if it is given adequate care. Optimum pH ranges
from 5.5 to 6.7. Overly acid soils are corrected by working
in lime at the rate of 1-2 tons/acre (2.4-4.8 tons/ha). On
rich organic soils the papaya makes lush growth and bears
heavily but the fruits are of low quality.
Papaya Propagation
Papayas
are generally grown from seed. Germination may take 3 to 5
weeks. It is expedited to 2 to 3 weeks and percentage of germination
increased by washing off the aril. Then the seeds need to
be dried and dusted with fungicide to avoid damping-off, a
common cause of loss of seedlings. Well-prepared seeds can
be stored for as long as 3 years but the percentage of germination
declines with age. Dipping for 15 seconds in hot water at
158º F (70º C) and then soaking for 24 hrs in distilled water
after removal from storage will improve the germination rate.
If germination is slow at some seasons, treatment with gibberellic
acid may be needed to get quicker results.
To
reproduce the characteristics of a preferred strain, air-layering
has been successfully practiced on a small scale. All offshoots
except the lowest one are girdled and layered after the parent
plant has produced the first crop of fruit. Later, when the
parent has grown too tall for convenient harvesting the top
is cut off and new buds in the crown are pricked off until
offshoots from the trunk appear and develop over a period
of 4 to 6 weeks. These are layered and removed and the trunk
cut off above the originally retained lowest sprout which
is then allowed to grow as the main stem. Thereafter the layering
of offshoots may be continued until the plant is exhausted.
Rooting
of cuttings has been practiced in South Africa, especially
to eliminate variability in certain clones so that their performance
can be more accurately compared in evaluation studies. Softwood
cuttings made in midsummer rooted quickly and fruited well
the following summer. Cuttings taken in fall and spring were
slow to root and deficient in root formation. The commercial
cultivar 'Honey Gold' is grown entirely from cuttings. Once
rooted, the cuttings are planted in plastic bags and kept
under mist for 10 days, and then put in a shade house for
hardening before setting in the field.
Hawaiian
workers have found that large branches 2-3 ft (60-90 cm) long
rooted more readily than small cuttings. Planted 1 ft (30
cm) deep in the rainy season, they began fruiting in a few
months very close to the ground.
In
budding experiments both Forkert and chip methods have proved
satisfactory in Trinidad. However, it is reported that a vegetatively
propagated selected strain deteriorates steadily and is worthless
after 3 or 4 generations.
In
Hawaii, 'Solo' grafted onto 'Dwarf Solo' was reduced in vigor
and productivity, but 'Dwarf Solo' grafted onto 'Solo' showed
improved performance.
In
recent years, the potential of rapid propagation of papaya
selections by tissue culture is being explored and promises
to be feasible even for the establishment of commercial plantations
of superior strains.
Efforts
have been made to determine the sex of seedlings in the nursery,
Indian scientists making colorimetric tests of leaf extracts
have had 87% success in identifying seedlings as female; 67%
in classifying males/bisexuals grouped together.
Papaya Variable
Season
Planting
may be done at any time of year and local conditions determine
when it is best for the crop to come in. Papayas mature in
6 to 9 months from seed in the hotter areas of South Africa;
in 9 to 11 months where it is cooler, providing an opportunity
to supply markets in the off-season when prices are high.
Seeds planted in early summer or midsummer will produce the
first crop in the second winter. Thereafter, the same plants
will mature fruit from spring to early summer.
Spring
fruits are apt to be sunburned because of winter leaf loss;
are also subject to fruit spot and have a low sugar content.
Sunburn can be avoided by advance whitewashing of sides exposed
to the afternoon sun. Some growers manipulate the harvest
season by stripping off 6 of the newly set fruits, thus forcing
the plant to bloom again and produce fruits 6 to 8 weeks later
than they normally would.
In
southern Florida, plants set out in March or April will ripen
their fruits in November and December and have the advantage
of a "tourist" market. July plantings will be slowed down
by winter and will not fruit for 10 months or more. Some growers
advocate planting in September and October so that the crop
will be ready for harvest before the onset of the main hurricane
season. Further north in the state, papayas must be set out
in March or April in order to have the required growing season
before frost.
Papaya Culture
Seeds
may be planted directly in the field, or seedlings raised
in beds or pots may be transplanted when 6 weeks old or even
up to 6 months of age, though there must be great care in
handling and the longer the delay the greater the risk of
dehydrated or twisted roots; also, transplanting often results
in trunk-curvature in windy locations.
Experiments
in Hawaii indicate that direct seeding results in deeper tap-roots,
erect and more vigorous growth, earlier flowering and larger
yields.
In
Puerto Rico, it is customary to set 2 plants per hole. In
El Salvador planters place 5 to 6 seeds, separated from each
other, in each hole at a depth of 3/8 in (1 cm). When the
plants bloom, 90% of the males are removed, preferably by
cutting off at ground level. Pulling up disturbs the roots
of the remaining plants. If the plantation is isolated and
there is no chance of cross-pollination by males, all the
seed will become female or hermaphrodite plants. Fruits should
mature 5 to 8 months later.
In
India, seeds are usually treated with fungicide and planted
in beds 6 in (15 cm) above ground level that have been organically
enriched and fumigated. The seeds are sown 2 in (5 cm) apart
and 3/4 to 1 1/8 in (2-3 cm) deep in rows 6 in (15 cm) apart.
They are watered daily and transplanted in 2 1/2 months when
6 to 8 in (15-20 cm) high. Transplanting is more successful
if polyethylene bags of enriched soil are used instead of
raised beds. Two seeds are planted in each bag but only the
stronger seedling is maintained. Transplanting is best done
in the evening or on cloudy, damp days.
On hot, dry days, each plant must be protected with a leafy
branch or palm leaf stuck in the soil. Except for 'Coorg Honey
Dew' and 'Solo', the plants are set out in 3's, 6 in (15 cm)
apart in enriched pits. After flowering, one female or hermaphrodite
plant is retained, the other two removed. But one male is
kept for every 10 females. 'Coorg Honey Dew' and 'Solo' are
planted one to a pit and no males are necessary. Watering
is done every day until the plants are well established, but
overwatering is detrimental to young plants. Double rows of
Sesbania aegyptiaca are planted as a windbreak.
The
installation of constant drip irrigation (12 gals per day)
has made possible papaya cultivation on mountain slopes on
the relatively dry island of Maui which averages 10 in (25
cm) of rain annually.
Papaya
plants require frequent fertilization for satisfactory production.
In India, best results have been obtained by giving 9 oz (250
g) of nitrogen, 9 oz (250 g) of phosphorus, and 18 oz (500
g) potash to each plant each year, divided into 6 applications.
Because
of the need to expedite growth and production before the onslaught
of diseases, Puerto Rican agronomists recommend treating the
predominantly clay soil with a nematicide before planting,
giving each plant 4 oz (113 g) of 15-15-15 fertilizer at the
end of the first week, and each month thereafter increasing
the dose by 1 oz (28 g) until the beginning of flowering,
then applying .227 g per plant as a final treatment. In trials,
this program has permitted 6 harvests of green fruits for
processing, each over 1 lb (1/2 kg) in weight, spanning a
period of 13 months. The roots usually extend out beyond the
leaves and it is advisable to spread fertilizer over the entire
root area.
In
late fertilizer applications of a crop destined for canning,
nitrogen should be omitted because it renders the fruit undesirable
for processing. High nitrate content in canned papaya (as
with several common vegetables) removes the tin from the can.
To avoid nitrogen deficiency at the beginning of flowering
for the next crop, 1 or 2% urea sprays can be applied.
In
southern Florida, on oolitic limestone, experts have prescribed
liquid fertilizer weekly for the first 10 weeks and then 1
lb (1/2 kg) of 4-8-6 dry fertilizer mixture (with added minor
elements) per plant weekly until flowering. Here a heavy organic
mulch is desirable to conserve moisture, control weeds, keep
the soil cool, and help repel nematodes.
Mechanical
cultivation between rows is apt to disturb the shallow roots.
judicious use of herbicides is preferable.
Overcrowded
fruits should be thinned out when young to provide room for
good form development and avoid pressure injury. Cold weather
may interfere with pollination and cause shedding of unfertilized
female flowers. Spraying the inflorescence with growth regulators
stops flower drop and significantly enhances fruit set. After
the first crop, the terminal growth may be nipped off to induce
branching which tends to dwarf the plant and facilitates harvesting.
However, unless the plants are strong growers, fruiting branches
may need to be propped to avoid collapse.
Papaya Harvesting
Studies
in Hawaii have shown that papaya flavor is at its peak when
the skin is 80% colored. For the local market, in winter months,
papayas may be allowed to color fairly well before picking,
but for local market in summer and for shipment, only the
first indication of yellow is permissible. The fruits must
be handled with great care to avoid scratching and leaking
of latex which stains the fruit skin. Home growers may twist
the fruit to break the stem, but in commercial operations
it is preferable to use a sharp knife to cut the stem and
then trim it level with the base of the fruit. However, to
expedite harvesting of high fruits, most Hawaiian growers
furnish their pickers with a bamboo pole with a rubber suction
cup (from the well-known "plumber's helper") at the tip. With
the cup held against the lower end of the fruit, the pole
is thrust upward to snap the stem and the falling fruit is
caught by hand. One man can thus gather 800-1,000 lbs (363-454
kg) daily.
In
Hawaii, it has been calculated that manual picking and field
sorting constitute 40% of the labor cost of the crop (1,702
man-hours per acre to pick and pack). Therefore, in 1970,
an experimental mechanical aid was tested and results indicated
that a machine with one operator and 2 pickers could harvest
1,000 lbs (454 kg) of fruit per hour, the equivalent of 8
men hand-picking.
Many factors, such as investment, operation and repair costs,
useful life, and so forth must be considered before such a
machine could be determined to be feasible. On the island
of Maui, harvesting is aided by hydraulic lifts, each operated
by a single worker. Picking starts when the plants are 11
months of age and continues for 48 months when the trees are
25 ft (7.5 m) high, too tall for further usefulness.
The
fruits are best packed in single layers and padded to avoid
bruising. The latex oozing from the stem may irritate the
skin and workers should be required to wear gloves and protective
clothing.
Papaya Yield
In
the usual papaya plantation, each plant may ripen 2 to 4 fruits
per week over the fruiting season. Healthy plants, if well
cared for, may average 75 lbs (34 kg) of fruit per plant per
year, though individual plants have borne as much as 300 lbs
(136 kg). In South Africa, branched 'Honey Gold' plants set
20 ft (6 m) apart in rows 10 ft (3 m) apart have produced
45 lbs (100 kg) of fruit each in their 4th year. A field of
1,000 plants occupying 2 1/2 acres (1 ha) gave 30 tons of
fruit. In the Hilo area of the island of Hawaii, production
averages 15 tons per acre (37 tons/ha). From 250 acres (100
ha), Princess Orchards on Maui harvests 150,000 lbs (68,180
kg) weekly during the season.
In
the Kapoho region of the island of Hawaii, yields average
38,000 lbs/acre (roughly 38,000 kg/ha) the first year, 25,000
lbs (11,339 kg) the second year. Papaya plants bear well for
2 years and then productivity declines and commercial plantings
are generally replaced after 3-4 years. By that time they
have attained heights which make harvesting difficult.
Papaya Renovation
of Plantings
In
Trinidad and Tobago, plants that have become too tall are
cut to the ground and side shoots are allowed to grow and
bear. In El Salvador, after the 3rd year of bearing, the main
stem is cut off about 3 ft (1 m) from the ground at the beginning
of winter and is covered with a plastic bag to protect it
from rain and subsequent rotting. Several side shoots will
emerge within a few days. When these reach 8 in to 1 ft (20-30
cm) in height, all are cut off except the most vigorous one
which replaces the original top.
Postharvest
Treatment
Fruits
can be held at 85º F (29.64º C) and high atmospheric humidity
for 48 hours to enhance coloring before packing. Standard
decay control has been a 20-minute submersion in water at
120º F (49º C) followed by a cool rinse. In India, dipping
in 1,000 ppm of aureofungin has been shown to be effective
in controlling postharvest rots. In Philippine trials, thiabendazole
reduced fruit rot by 50%. In 1979, Hawaiian workers demonstrated
that spreading an aqueous solution of carnauba wax and thiabendazole
over harvested fruits gives good protection from postharvest
diseases and can eliminate the hot-water bath.
In
Puerto Rico, fruits of 'P.R. 8-65', picked green, were ripened
successfully by 6-7 days treatment with ethylene gas in airtight
chambers at 77º F (25º C) and 85 to 95% humidity, following
the hot-water bath.
Hawaiian
papayas must be sanitized before shipment to the mainland
USA to avoid introduction of fruit flies. Fruits picked 1/4
ripe are prewarmed in water at 110º F (43.33º C) for about
40 min, then quickly immersed for 20 min at 119º (48.33º C).
This double-dipping maybe replaced by irradiation. One little-used
method is a vapor-heat treatment following dry heat at 110º
F (43.33º C) and 40% relative humidity.
Fruits
that have had hot water treatment and EDB fumigation and then
have been stored in 1.5% oxygen at 55º F (13º C) for 12 days
will have a shelf life of about 3 1/2 days at room temperature.
Fruits that have had hot water treatment when 1/4 colored,
followed by irradiation at 75-100 krad, and storage at 2-4%
oxygen and 60º F (16º C) for 6 days will have a market life
of 8 days. Those held for 12 days will be saleable thereafter
for 5 days.
In
Puerto Rico, gamma irradiation (25-50 krads) delayed ripening
up to 7 days. Treatment at 100 krads slightly accelerated
ripening in storage. Even at the lowest level irradiation
inhibited fungal growth. Carotenoid content was unaffected
but ascorbic acid was slightly reduced at all exposures.
Partly
ripe papayas stored below 50º F (10º C) will never fully ripen.
This is the lowest temperature at which ripe papayas can be
held without chilling injury.
'Solo
62/3' fruits harvested in Trinidad at the first sign of yellow,
treated with fungicide, placed in perforated polyethylene
bags and packed in individual compartments in cartons, have
been shipped to England by air (2 days' flight), ripened at
68º F (20º C), and found to be of excellent quality and flavor.
The
same cultivar, similarly handled, withstood transport in the
refrigerated hold of a ship for 21 days. Immediately ripened
on arrival, the fruits were well accepted on the London market.
Sea shipment proved to be the more economical.
Hypobaric
(low pressure) containers have made possible satisfactory
sea shipment (18-21 days) of hot-water treated and fungicidal-waxed
papayas from Hilo, Hawaii, to Los Angeles and New York.
Papaya Pests
A
major hazard to papayas in Florida and Venezuela is the wasp-like
papaya fruit fly, Toxotrypana curvicauda. The female
deposits eggs in the fruit which will later be found infested
with the larvae. Only thick-fleshed fruits are safe from this
enemy. Control on a commercial scale is very difficult. Home
gardeners often protect the fruit from attack by covering
with paper bags, but this must be done early, soon after the
flower parts have fallen, and the bags must be replaced every
10 days or 2 weeks as the fruits develop. Rolled newspaper
may be utilized instead of bags and is more economical. India
has no fruit fly with ovipositor long enough to lay eggs inside
papayas.
An
important and widespread pest is the papaya web-worm, or fruit
cluster worm, Homolapalpia dalera, harbored between
the main stem and the fruit and also between the fruits. It
eats into the fruit and the stem and makes way for the entrance
of anthracnose. Damage can be prevented if spraying is begun
at the beginning of fruit set, or at least at the first sign
of webs.
The
tiny papaya whitefly, Trialeuroides variabilis, is a
sucking insect and it coats the leaves with honeydew which
forms the basis for sooty mold development. Shaking young
leaves will often reveal the presence of whiteflies. Spraying
or dusting should begin when many adults are noticed. Hornworms
(immature state of the sphinx moth-Erinnyis obscura in
Jamaica, E. ello in Venezuela, E. alope in Florida)
feed on the leaves, as do the small, light-green leafhoppers.
Mention
is made later on of the aphids that transmit virus diseases
and other infections.
Other
pests requiring control measures in Australia include the
red spider, or red spider mite, Tetranychus seximaculatus,
which sucks the juice from the leaves. In India and on
the island of Maui, plant and fruit infestation by red spider
has been a major problem. This pest and the cucumber fly and
fruit-spotting bugs feed on the very young fruits and cause
them to drop. In Hawaii, the red-and-black-flat mite feeds
on the stem and leaves and scars the fruit. The broad mite
damages young plants especially during cool weather.
In
the Virgin Islands scale has been most troublesome, apart
from rats and fruit-bats that attack ripe fruits. In Australia,
5 species of scale insects have been found on papayas, the
most serious being oriental scale, Aonidiella orientalis,
which occurs on both the fruit and the stem. So far, it
is confined to limited areas. In Florida, the scale insects
Aspidiotus destructor and Coccus hesperidium
may infest bagged fruit more than unbagged fruit. Another
scale, Philaphedra sp., has recently been reported
here.
Indian
scientists have observed that immature earthworms, Megascolex
insignis, are attracted by and feed on rotting tissue
of papaya plants. They hasten the demise of plants afflicted
with stem rot from Pythium aphanidermatum and may act
as vectors for this fungus.
Root-knot
nematodes, Meloidogyne incognita acrita, and reniforin
nematodes, Rotylenchulus reniformis, are detrimental
to the growth and productivity of papaya plants and should
be combatted by pre-planting soil fumigation if the nematode
population is high.
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