AGRICULTURAL EXTENSION SERVICE
(Circular 133 May 1955
By RoY W. HARNESS
1Assistant Chemist, Sub-Tropical
Papayas have been grown in Florida for nearly half a century
and have been widely publicized at times. Nevertheless, the
market for the fruit has always been linilel and the acreage
has remained comparatively small, never more than a few hun-
dred acres. Since the plants will produce fruit within a year
after planting, usually there has been overproduction within a
year or two after each period of high prices. However, there
has been a gradual increase in consumption and during the last
few years the industry has been fairly stable.
Most of the larger growers or prospective growers seem to
realize that increasing the acreage only a hundred acres or so
might cause serious overproduction.
CLIMATE AND SOIL
The papaya is very sensitive to frost, although it is not as
limited in range as some tropical plants. It will be severely dam-
aged by exposure to 310 temperature but a large plant may not
be killed until exposed for a considerable time to somewhat
lower temperatures. Papayas have been grown in backyards
as far north as St. Augustine but commercial plantings are all
located in more nearly frost-free areas. Even in the vicinity
of Miami there is sufficient frost every few years to cause se-
vere d;1n;i-a if frost protection is not supplied.
The papaya thrives on almost any type of soil, provided there
is adequate drainage. Large amounts of fertilizer are required
on poor soil but, when well fertilized, high sandy or limerock
soils will produce large crops of good quality fruit. On a rich
soil, such as the muck of the Everglades, tremendous crops are
produced but the fruit is likely to be of poor quality.
Low, marshy ground, or that subject to periods of overflow,
should be avoided for growing papayas. Water standing around
the crown roots for a period of 48 hours is likely to prove
fatal to the plant.
FLOWER TYPES AND SEED SELECTION
Papaya plants may be "male", "female" or "bisexual". Sex
of the plant can be determined only when flowers are produced.
Male Iil:;tI. are easily recognized by the long hanging panicles
on which the flowers are produced in clusters. These plants
ordinarily do not bear fruit. Female and bisexual plants have
flowers which are clustered at the base of the leaf next to the
stem. Female plants have flowers that lack stamens so they
must receive pollen from other plants in order to produce fruit.
Bisexual plants have complete or perfect blossoms with both a
pistil and 10 stamens but there is frequently a tendency for
plants of the bisexual type to revert to either the male or female
form. Bisexual plants that are more male than female may
have flowers with pistils only during the late winter and spring
months, so the plant will be barren a large part of the year.
Bisexual plants that are more female than male will have blooms
with less than 10 stamens. When two or more stamens are
missing the fruit will be more or less misshapen and may have
a crease on one side. Rotten spots frequently form in these
creases before the fruit reaches maturity.
Yield from the bisexual plants in a good strain of papayas
will average nearly as high as from the female plants. \,t-
markets prefer the cylindrical shape and small seed cavity char-
acteristic of bisexual fruit rather than the nearly round fruit
produced by the female flower.
Hand pollination can be done quite easily. To insure that a
bisexual blossom is self-pollinated, it is only necessary to fasten
a small paper bag over the blossom before it opens and leave
the bag on for several days until the ovary has started to en-
large. Cross-pollination may be done by placing male or bisexual
pollen on the pistil of a female blossom.
Hand pollination tests have shown that:
1. Female pollinated by male gives equal numbers of male
and female progeny.
2. Female pollinated by bisexual gives equal numbers of fe-
male and bisexual poi'tn,".
3. Bisexual pollinated by male gives equal numbers of fe-
male, bisexual and male progeny.
4. Bisexual self-pollinated gives 67'.; bisexual, with the bal-
In Florida male plants usually are not needed to pollinate
female blossoms if bisexual plants are present. However, male
plants are apparently more active pollinating agents. Ordi-
narily a large proportion of the seeds from any fruit grown in
the vicinity of male plants will reproduce male plants.
The only way to improve the type of papayas raised is to use
seed from selected hand-pollinated fruit. However, any seed
taken from good fruit in an isolated planting that has uni-
formly good quality plants will usually produce a large propor-
tion of good plants.
To establish a true variety in any crop that is reproduced by
seed, it is necessary to select carefully the plants for uniform
characteristics for several generations. Accordingly, there are
very few papaya varieties. Probably the most uniform variety
is Hawaiian Solo, which is the result of many years of papaya
breeding. This variety is not considered satisfactory in Florida,
however, because of its small size and poor yield. Most papayas
grown in Florida can better be described as types rather than true
varieties. The nearest to a true variety in Florida is probably
the Blue Solo, a cross between the Hawaiian Solo and a large blue-
stemmed papaya. It produces good yields of fairly uniform fruit
of good quality weighing 2 to 4 pounds.
The only practical method of propagating papaya is by seed.
Seeds should be started in small pots so the seedlings may be
set in the field without disturbing the roots. Cups made of felt
paper may be used but many growers use quart oil cans with
the bottom cut nearly out. When ready to set in the field the
soil is thoroughly moistened, the bottom of the can is turned
back, and the soil is pushed out as a solid cylinder.
A mixture of sand and muck or any other good. high organic
potting soil is satisfactory for growing the seedlings. Small
papaya seedlings are ,-li, ij t to damping-off, so sterilization of the
soil is a wise precaution. If soil sterilization is impractical, damp-
ing-off may be minimized by pJr.v'iliti the seedlings with good
aeration, avoiding excess water.
When using seed from fruit hand-pollinated with bisexual
pollen, two seeds to a pot are enough. With other seed there
will usually be a considerable proportion of male plants so it is
desirable to plant about five seeds to a pot and thin to three
plants. These three plants are allowed to grow until they blos-
som. The male and other surplus plants should then be re-
moved, leaving one bisexual or female plant in a hill. If no
bisexual plants are present, about one male plant per 20-25 fe-
male plants should be left for pollination.
The seedling pots should be watered frequently enough to
prevent the top inch of soil from 1 .., 'iiini dry but not enough
to saturate the soil r) -.i nt liy. It is advisable to apply a little
soluble fertilizer about once a week to potted seedlings.
Papayas should be planted 8 to 10 feet apart both in the
row and between rows, since the leaves of vigorously growing
plants will spread more than 5 feet from the trunk. For con-
venience in harvesting and spraying, a 15- to 20-foot driveway
should be left every four or five rows. The ground should be
thoroughly loosened to a good depth before planting. In the rocky
soils of Dade County the ground should be scarified quite deeply
and if the grniind has stood for a year or more after :..arif' ing it
should be dug up again. In compact soil on low ground, careful
irrtangenw-nt. should be made for di.ini;agt between the rows.
Plants should not be set any lower in the ground than they
were in the container. A handful of a mixed fertilizer such
as 5-7-5 should be placed in the hole around the plant and close
to it but not actually :,uain-t the roots. After filling the hole,
a mulch of grass, peat moss, shavings or other material should
be placed around the plants to help conserve moisture and pre-
vent growth of weeds around the small plants. In dry weather
the plants should be watered frequently until well established.
In cooler parts of the state plants should be set in the field in
March or April so as to give them the longest possible period
without danger of frost. In warmer sections, plants may be
set out at any time, but by planting in March or April it is
possible to get fruit by November or December. If planted
after July 1, the plants go through the winter season without
fruiting and would probably require 10 months or more to pro-
duce fruit. If planted in late summer, however, they probably
would not be damaged much by a hurricane in the fall and would
produce fruit for a time before the next hurricane season.
FERTILIZATION AND IRRIGATION
Papayas require quite large amounts of fertilizer. The actual
amount required depends on soil conditions, rainfall, etc., but
the foll..n ing schedule will serve as a rough guide. Beginning
a couple weeks after the plants are set in the field a standard
mixed fertilizer such as 5-7-5 with more than 25', of the nitro-
gen from organic sources and containing 3 units of available
clMO is used. This should be applied twice monthly, starting
with 11i, pound per hill and inc,'-.in,' gradually until at the
end of six months the rate is 1 pound. In addition to that, 5
to 10 pounds of organic fertilizer such as chicken manure, com-
mercial >-'va:\;I- sludge or tobacco stems may be put around the
plants when small. In any fertilizer prIwtgr'. it should be remem-
bered that a heavy rain may wash out most of the soluble nitro-
gen and potash. On the other hand, too high concentration of
fertilizer materials may be obtained if repeated applications are
made when there is no rain or irrigation.
In general, best results are obtained by keeping the plants
g.'irinig vigorously at all times. Usually either nitrogen or
water is the limiting factor in growth. As the plants get older
other elements also must be present to maintain healthy plants
and good quality fruit. If the bottom leaves turn yellow, a
nitrogen deficiency is indicated. A gradual yellowing of all the
leaves may indicate lack of water. It is desirable to keep the
bottom leaves green as long as possible because the growth of
the plant and the II;I ai and sugar content of the fruit are
directly dependent on the leaf surface. In applying fertilizer,
care should be taken to spread it over the whole feeding area of
the roots. Papaya roots usually extend out farther than the
,i-;glit of the plant.
Under Florida conditions it is frequently possible to double
the papaya crop by irrigation. Young plants are not extremely
sensitive to dry weather when first set in the field. But when
ri,,.\-,ri1 n starts, a week or so of dry weather may cause then
to drop their blossoms for a considerable time. Older plants
become somewhat resistant to drought but will not produce
full crops in dry weather. On shallow soils such as Dade County
lirlliie.. water may be needed every five or six days. Ex-
tending the interval to 10 days in warm dry weather might
result in as much damage from don'ghl as no ii ri!vali.1; .
When properly cared for, the papaya plant will continue bear-
ing good crops for at least, two years after the first fruit is
obtained. When the plants are three or four years old it is
generally advisable to abandon the Ipl.ltiiv. although the plant
may live much longer. When well cared for, plants should
average 75 pounds of fruit per year. Yields of .:'.I pounds of
fruit per year on individual trees are not unusual, but that
amount is much above the normal average.
CONTROL OF WEEDS, DISEASES AND PESTS
The control of weeds is very important, particularly around
the young plants. It is impossible to make the small plants
grow satisfactorily when they are surrounded by a heavy
growth of grass or weeds. The best method of control around
the young plants is to keep a mulch of dead grass, shavings
or other material for a distance of one or two feet from the
plant. This mulch also helps to conserve moisture and later
when it decomposes will combine with the added fertilizer to
give an organic source of nitrogen. When the plants get larger,
weeds can be controlled by cultivation. On shallow soil such as
Dade County limestone the only cultivation should be drag-
ging or hand hoeing. Mowing does not give adequate control
of weeds on shallow soil.
There are three insect pests that may be serious. The papaya
webworm, which invades the area between the fruit and trunk,
will ruin the fruit if it is not controlled. The papaya fruit fly,
which lays its eggs in the growing fruit, frequently causes the
ripe fruit to be full of maggots. The papaya whitefly is a very
small insect, individuals of which congregate primarily on the
young leaves near the growing tip of the plant. Black sooty
mold grows on the secretions and excretions of this insect. The
occurrence of this mold on leaves and fruit indicates a whitefly
infestation. This mold cuts down the capacity of the green
tissue to make food and makes the fruit unattractive.
A spray of 2 pounds of wettable DDT per 100 gallons of wa-
ter applied thoroughly on the trunk and fruit once a month
will give complete control of the papaya webworm. This same
spray usually will give good protection against the fruit fly if
all the papayas in the vicinity are sprayed. In a backyard plant-
ing, where the neighbor's plants may be untreated, it may not
be possible to control the fruit fly. A spray of 5-10 pounds of
wettable sulfur per 100 gallons will give good control of the
whitefly. The sulfur may be combined with the DDT.
There are two leaf-spot diseases that are difficult to control
but fortunately they seldom do enough damage to be serious.
Anthracnose and other fungus rots of the fruit usually cause
considerable loss. Excessive susceptibility to anthracnose seems
to be inherited, but all plantings will have some damaged fruit.
The disease is affected by various seasonal conditions, particu-
larly rainfall and high humidity. At present, no fungicidal
treatment is known that will give satisfactory control.
Powdery mildew, a fungous disease characterized by the
growth of a whitish mildew on the lower leaf surfaces, seldom
causes much damage but may be a contributing factor in caus-
ing the lower leaves to drop. It can be controlled with sulfur.
A defect typified by large lumps on the fruit and exudation
of latex at many points is quite common. The cause is unknown,
but susceptibility to it seems to be inherited. It appears to be
aggravated by freezing or near-freezing temperatures.
Virus diseases are probably the gravest threat to the Florida
papaya industry. Apparently several viruses may occur sepa-
rately or in combination in affected plants. Symptoms vary, but
usually the first is an irregular mottling of the youngest leaves.
Some areas become more transparent or yellow than normal
and the general effect is to lighten the color of the leaves. Later.
mottling or distortion will spread to all new leaves, irregular
greasy-appearing streaks may form on the leaf petioles and
stem, and the fruit will develop spots that usually become ir-
regular rings less than an inch in diameter. These character-
istic rings may be considered positive identification. These rings
do not always develop, but at other times they may occur before
mottling of the leaves can be detected. Mii plants are badly
damaged by these diseases and practically stop growing. In-
fected plants will start producing fruit with objectionable flavor
within two or three months after symptoms are visible. How-
ever, some infected plants may seem to be only mildly affected
as long as good growing conditions exist, but they may fail to
recover from adverse conditions such as flooding, low fertility.
extreme drought or cold weather.
Conditions other than virus diseases may cause deviations in
the normal green color of papaya leaves. Light colored young
leaves may be caused by root damage or lack of fertilizer, so if
no mottling is present virus diseases need not be suspected.
Powdery mildew will cause the leaves to become mottled. In
warm weather, DDT spray will mottle the tender leaves. When
that occurs the spots usually appear suddenly shortly after
spraying. If the plants are watched for a couple of weeks, new
leaves will be seen to come out without spots. Heavy infesta-
tations of whitefly also may cause a mottling of young leaves.
Papaya virus diseases apparently are not spread by seed and
apparently not easily spread by contact. There is no reason to
believe that they are spread by workmen in the field. In a
large field, most newly infected plants will be clustered about
a diseased plant, but some will be at a considerable distance.
It is suspected that the disease is spread by certain insects
but no such insect has been identified as a carrier of Florida
papaya virus diseases. There is no evidence to suggest that any
spray would control the disease.
The only known control of virus diseases is to cut the plants
down as soon as the virus symptoms are detected, but this
method is not effective in all cases. Over a three-year period
in an isolated large planting of papayas of several ages, infected
plants were removed each week. For the first two years, in-
fected plants removed averaged about 0.39; of the total number
each week, or 15 each year. However, during the third year a
new planting )lnul,-rii' the older plants was set out and the
plants were inspected and diseased plants rogued each week.
Two-thirds of the plants in the younger planting were re-
moved before they were in the field eight months. In spite of
that, roguing continued to be effective in the older planting for
another three months. Then the number of infected plants per
week in the older pIlaniing suddenly increased from less than 1.0
to more than 2.0% and both plantings were lost.
When infected plants were left in the field most iiighlbrin-:
plants were infected within a month. The spread was much
slower to plants only 50 or 100 feet away. In other groves where
infected plants were left the infection usually has been 100%
within a very few months after 5'. of the plants are atffecte'
Roguing, to be even partially successful, must be started while
the proportion of diseased plants is very small and is most effec-
tive in isolated plantings.
Some growers leave the virus infected plants in the field so
as much fruit as possible may be salvaged. When the infection
does not become severe until the fruit starts to ripen that may
be advisable, but there is little hope that the harvest will con-
sist of much more fruit than is already set. Also, later-matur-
ing fruit will probably be of very poor quality.
In spite of the seriousness of the virus disease problem, it is
believed that papayas will continue to be raised successfully in
Florida. The virus diseases have been present for at least
eight years but papaya production has been increasing each
year. Up to now, most losses have been in plantings where
infected plants were not removed.
COOPERATIVE EXTENSION WORK IN
AGRICULTURE AND HOME ECONOMICS
(Acts of May 8 and June 30, 1914)
A ImrICr:LTrIAL EXTENSION SERVICE, UNIVERSITY OF FLORIPT
FLORIDA STATE UNIYV'ERITY
IND UINI1TED STATEs DEPARTMENT O.r Ar CI:ImncrTT
II. G. CLAY'TON. DT)IRE:rTro