c5 ^ruii Suitable for South Florida
Scott U. Stambaugm
Mr. Stambaugh has been experimenting with papayas longer than anyone else in the state and has been employed for two years in the Bahamas as an expert in developing the industry.
T. J. Brooks Assistant Commissioner of Agriculture
It's Jirvodiiiii itn,l Commercial Uses
The papaya is a soft stemmed annual, a plant not a tree, it is possible to plant seed, grow plants, set them in the lickt. grow a crop, harvest fruit and get out of the fruit mature seed to plant again, all within the space of one year. This is a statement of facts and is important because it to some extent dictates what the practice shall be in every function of the culture and use of this crop.
The bleeder and grower groups must both realize that they are dealing with a quick growing lush truck crop that must be handled as such all along the line. It is of prime importance to the grower, particularly, that he understands in the beginning that this is not a tree crop and cannot be treated as one if satisfactory crops are to be produced. The appearance of this crop taken together with the fact that it will survive for a number of seasons has too often led the grower into treating his papaya planting as he would his citrus planting with poor or even disastrous results. It is not too much to say that this misunderstanding of the nature of the crop has led to more failures than all other factors put together.
The papaya grower should from the time he starts to prepare soil for seed flats in which to grow plants, use the same care he would in the growing of the most sensitive and demanding of truck crops. The crop should never be allowed to suffer a check from the time the seed go into the ground, if it can be avoided. It is a fact that the papaya as a crop will sometimes absorb a lot of grief and still make some fruit. It is still true that if the crop is checked by any adverse factor at any period in its growth the results in quantity and quality of fruit will not be as good.
The papaya is under Florida conditions an ideal crop for the grower who is willing to give intensive care and attention to one or two acres. The very high possible return in tons of fruit per acre per year contributes to this, and where the grower is so located as to be able to sell all he produces himself locally a single acre will make a moderate living and two acres a very decent living. Annual yields of one hundred pounds to the plant per year are possible, but one half that are a lot more common. No crop in Florida will give the grower the returns for undivided attention that this one will. The opposite is also true, for no crop will lose the grower more money per acre if treated
to a little carelessness at vital points, because of the high cost per acre in labor and money of the crop; and the ease with which frost or flood can destroy it.
In appearance the papaya plant is sometimes compared to the palm. This is a matter of superficial appearance only. The plant is in fact nothing like the palm. There is a single, tall, straight, fleshy plant stem that may be anywhere from six to thirty-five feet tall. At the top of this plant stem there is ordinarily a single terminal bud surrounded by a crown of large leaves on long stems. A well grown papaya plant is as wide across its flat top as it is tall 'til after it reaches ten feet high.
If this plant has a bad structural weakness, it is this single plant stem, single bud arrangement. There are two reasons for the weakness of this arrangement: first, the plant stem becomes smaller as it grow tall and is in direct proportion to the decrease in diameter, not as good a pipeline for water and plant foods from tbe roots; second, the single bud tends to grow weaker as seasons go by and does not produce a large enough crown of leaves to function properly as the producer of starches and sugars. It is possible in cultural practice to induce the plant to make several plant stems and leaf crowns at a time and to replace the older ones periodically with new ones. This leads to longer lived plantations and higher average crops during the entire life of the plantation.
The fruit of the papaya is melon-like and resembles the cantaloupe more than anything we have in the temperate climate. It is, in fact, often called the cantaloupe that grows on a tree. There is a large variation in all fruit characters of the cultivated forms of papaya even when plantings have been made from the seed of a single melon. This has in the past been the principle deterant to the large scale papaya commercialization. Variation from plant to plant has been too great for successful and profitable adaptation of the crop to commercial uses, even where the planting stock was the result of the best effoi'ts of the plant breeders.
In size, the fruit may be anything from that of a walnut to twenty-five pounds. There are an infinite number of shapes running through spherical, eggshape, pearshape, to almost perfectly cylindrical. There are all variations of these general shapes through hybridization. There is just as wide a variation in flesh character, thickness, texture, color, flavor and degree of sweetness may be almost anything; and the different combinations of these things result
in melons that are rarely the equivalent of the best of the i-aiitaloupcs but are too often actively distasteful. The -..ds are attached to the inside of the melon by a membraneous aril, much as are the seeds of the cantaloupe. The seeds are small, grey or black and have an exterior ji-llatinous appearance due to the fact that each seed is i-nrlosed in a sack filled with a clear limph-like liquid. When ilry the seeds are a little larger than mustard seed but are enclosed in a corky ridged seed cover that makes them appear much larger.
This matter of the great variability of papaya is an expression of the peculiarities of its genetic make-up and has not in the past been too well understood. During the past six years work along two different lines has had a ieiidency to clear these things up. Because of work done with the assistance of the Bureau of Plant Industry Station at Orlando, some light has been shed on the problems of breeding papaya. Also work along the lines of a sexual propagation has gone a long way. A method of grafting lias been worked out that is feasible at least in the hands of a trained operator and some advance has been made in t!.<. matter of rooting cuttings that will have to be carried further. By grafting it will now be possible to spread the characters of a proven seedling over at least a thousand plants to set out. Whether or not grafts can be taken from grafted plants that will be successful has yet to be proven, so that the annual production of some desirable seedlings as the result of breeding programs is still a matter of necessity.
The papaya is strictly a New World plant and came to the attention of Europeans with the discovery and conquest of the western continents. This plant as a cultivated form probably originated in Northern Central America or even Southern Mexico. The first line of distribution was probably down the west coast of Central America and then out ever the old Inca trade route. By the time Europeans arrived on the scene the papaya had spread both as a cultivated plant and as a wild escape all over Mexico, Central America, Northern South America, the West Indies and Florida.
The primitive or wild papaya whether it exists as an indigenous form or as an escape is a vigorous rapid grower and is tolerant of a wide range of climatic and soil conditions. The cultivated forms on the other hand are inclined to be demanding as to situation and care. The existence of this plant as a wild form should by no means be taken
as assurance that the cultivated forms can be adapted. There is an astonishing uniformity of all characters, plant or fruit, among the wild forms. Just the opposite is true of the cultivated forms. There is probably no crop plant that shows the variability that the papaya does under conditions of general adaptation to the use of man.
During the first hundred years after the Conquest the papaya was distributed all over the tropical belt of the world and had in a number of places crept off into the semi-tropical parts. For more than two centuries now no other plant has been as universally common a door-yard plant wherever in the world the climate is mild enough for it to grow.
It is a little hard to see just why this plant has so long remained almost solely a door-yard plant. In this category it has become very useful to the populations that are so located that they can grow it. Yet up to about thirty-five years ago it had not become the subject of any very large
Fig. 1.Close up view of clustered papaya.
field enterprises anywhere in the world. Almost anywhere in the tropical world the native family has had, during 'In- last hundred years, a few plants in the door-yard. They made use of the fruit themselves and on market days ,anied a few to market when they went for some other reason. They did not, however, make any extended effort in commercialize the culture or to improve the character if the fruit.
Paring the last thirty-five or forty years the U. S. D. A., and a number of independent workers in Florida and Hawaii have done more orderly work with this plant than had been done all over the world before that time. The same is true of commercial efforts in Florida and Hawaii. Probably, because the incentive was there in the form of the prices the American public has been willing to pay for fresh fruit and products. The commercialization of the growing and processing has come a long way in Florida and Hawaii, particularly in the past fifteen years.
It is settled that the people of the United States want papaya and will pay for it. It is also settled that they will not buy or pay anything for papaya that they do not con--iiler nice dessert fruit. All over the tropics papaya are sold in vast quantities that would never get to first base in the United States. This is an expression of the great variety of fresh fruit from which our people have to choose at all times of the year. If what is offered is not of the best quality then continuous purchases just do not occur.
During the past forty years the U. S. D. A. has introduced to Florida something like one hundred and fifty more or less distinct varietal forms of the single species carica papaya. Under conditions in Florida these have hybridized at will among themselves and with the wild form. The result has been chaos, there are literally thousands of varietal forms that are fractionally hybridized and nearly all are contaminated to some extent with the undesirable wild form. Very few of them are of any real use either as producers of usable fruit or as material for use in breeding of plants that might be.
All this multiplicity of hybrid types has had an unfortunate effect on the growers of papaya. The general attitude is that papaya are what they are, and not much can be done about it. This has contributed to the slowness with which the industry has developed, because it has resulted in the production each year of a mass of fruit whose quality the buyer could not depend on for any particular use. During the past ten years there has been
some tendency for a few more stable forms of papaya to emerge out of the chaos that was the past.
There is still much to be desired in the development of papaya types that will be adaptable to the several uses that have shown up for fruit of specific character. It is to be expected that the newly discovered method of grafting papaya will speed the day when there will be specific types of fruit for specific uses. It is, of course, necessary and desirable that the grower have a rather exact idea of what is useful in the way of fruit characters for specific purposes. The best road to that is the reaction of the buying public and by that process the picture is becoming clearer.
The experience of the past twenty-five years gives a rather accurate picture of what it takes to make a satisfactory papaya for the fresh fruit trade. Such a fruit should weigh from two to three and a half pounds; should be as nearly cylindrical in shape as possible; should have thick smooth-textured flesh with no fiber, of dark yellow or orange color; should be sweet to the taste, and must be entirely free of the musky odor and flavor that comes with the contamination with blood of the wild form.
The processor wants the same general type of fruit with the exception that processors fruit should be as large as is reasonably possible, because the larger the fruit the better the return of usable material out of each fruit.
To satisfy all of these conditions the ideal fruit must come from the plants that are of perfect flowered form. The fruits of the perfect flowered plants just as they run have a greater tendency to be smooth-textured and firni-fleshed even when ripe enough to eat than the fruits of the female plants. The shape of the fruits of the perfect flowered plants are apt to be long cylindrical and even when considerably larger at one end they pack better in the case than the irregular shapes of the female plants. These are general conditions that apply as a matter of the sex of the plants rather than being controlled by the particular varietal form.
Quite probably as a result of the preceding paragraph there has been a growing tendency on the part of wholesale people in the northern markets to object if even a few of the globular fruits of the female plants were included in the boxes.
BREEDING OF COMMERCIAL USEFUL TYPES OF PAPAYA
This has been for a long time a controversial subject and will continue to be for a long time yet. On the basis that controversies do bring out the facts in time, that is as it thiillld bo. A lot of the technical details of papaya breeding have in the past been so obscure that the best men in it were to a large extent guessing from a little information toward a direction that they hoped was the right one. A lot of the obscurity has been cleared up in the last six years at least in the details of practice. The theory of the i|ing still needs a lot of clearing up. The problems have tioen aggravated by the fact that most of the papaya breeders have been little more than papaya enthusiasts. Kach of these enthusiasts believed in his own group of mixed hybrids and was willing to make considerable personal sacrifice to keep them on the market.
A lot of this will be modified by the new technique of grafting. It was one thing for a grower to hang on to his variable mixed strain of papaya seedlings and keep their fruit on the market by main strength awkwardness when every one was in more or less the same position. It will now be another problem, because any breeder who can produce a few good seedlings each year will be able to produce from them by grafting many thousands of type plants. These thousands of plants will go into the field and produce fruit of exactly uniform character after the pattern of the >eedlings. It is hard to forecast what this matter of grafting will mean, but the results can hardly be otherwise than good.
Before trying to discuss the breeding of papaya it would probably be best to try to clarify the matter of names and peculiarities of the several sex forms of papaya.
the male plant, the coke type male
This sex form has been regarded as purely male in its function. That is as solely a producer of pollen for the fertilization of the flowers of the female plants. It has always been known that these plants occasionally produced hermaphrodite flowers and bore fruit but these were regarded as individual sex freaks rather than as an expression of the inherent characteristics of the sex form. It has now been demonstrated that all male plants will bear fruit under stimulus of the right character.
It become necessary then to regard this sex form not as a male plant but rather as an hermaphrodite that docs not under normal conditions function as such.
This forces rather a radical change in the ideas as to the functional behavior of this sex form in breeding. The probability is that this sex form behaving as a male should be regarded as functioning in exactly the same manner as would the normally bearing hermaphrodite when functioning as a male. This theory is to some extent substantiated by the fact that when the core male bears under climatic stimulus a full crop of fruit, then genetic pattern as expressed in the variations of flower forms and the fruit that follows them is exactly that of the bearing hermaphrodite.
It follows then that the bearing hermaphrodite can be expected to serve the same purpose as the core male in exactly the same way and that because the bearing hermaphrodite regularly produces fruit. The problem of keeping fruiting characters in line will be easier.
the type hermaprod1te, perfect flowered form, ri-sexual plant
This sex form produces both fruit and pollen in the same flowers under normal conditions. It also produces flowers that resemble those of the male plant but have generally been supposed not to contain viable pollen. There has been a theory since the days of De Candole that this sex form could be, by repeating selfing run out to a pure form, as to sex as well as to other characters. This theory has now been completely disproven.
the female papaya plant
This form is and always has been regarded as purely female. It now stands out as the only genetically simple and dependable thing about papaya. It is a bearer of fruit and seed, nothing less and nothing more, and requires the pollen from one of the two types of hermaphrodites to produce seed. It is the only member of the papaya family that has an inherent tendency to transmit its characters in an orderly manner.
To sum up this matter of sex forms of the papaya: It becomes evident that what we have in the species carica papaya is two forms of hermaphrodites, one that normally functions as a bearer of fruit, one that does not, and a female plant. This is opposed to the old theory that there was a single male form, a single female form, and a single hermaphrodite form.
BREEDING PECULIARITIES OF SEX FORMS
The female sex form has been classified by Beaumont of Hawaii as homozygous, that is capable of transmitting its characteristics to progeny much as they were in the parent plant. This seems to be the case but is complicated by the i'avl that this form to produce seed must have pollen from .me of the two forms of hermaphrodites.
The male sex form is permanently heterozygous, that is capable of transmitting characters to progeny only in a variable manner than cannot be forecast. This form can probably be dismissed as incapable of serving any purpose thai would not be better served by the bearing hermaphrodite.
The hermaphrodite: This form normally bears fruit but functions perfectly as a male for the purpose of furnishing pollen to any females that may be in its vicinity. The fact that this form normally bears fruit makes it reasonably clear what sort of fruit characters it will transmit to its progeny. Whether the progeny are arrived at by using its own pollen to self its own flowers or to fertilize the (lowers of a female plant is a modifying detail only. If the pollen of an hermaphrodite is used to fertilize the (lowers of a female plant that is a full sister, then the probability is that the hermaphrodite children of that mating will show an increased tendency to breed true to the selected ancestor in all plant and fruit characters. This is the most important discovery of recent years with regard to the breeding of papaya.
The bearing hermaphrodite has one breeding peculiarity that has in the past been a serious stumbling block. De ( andole the French botanist offered the theory that any selected bearing hermaphrodite plant with a set of desirable characters could be run out to a pure strain that would breed true in all of its seedlings by successive generations of enforced self pollenation. This is true only to a limited extent and the difficulty that arises is due to the fact that the bearing hermaphrodite in the papaya is not a normal hermaphrodite form. There are peculiarities in the genetic set-up that are not yet completely understood.
It is possible to select a given hermaphrodite plant having a desirable set of plant and fruit characters as the start of a new strain. It. is possible to self that plant and "elect from its progeny those hermaprodite seedlings that are nearest in line with the selected parent. This second generation of selected hermaprodite seedlings can then be grown off and subjected to enforced self pollenation. Their
progeny can then be selected for identical seedlings, that are hermaphrodite in character and in line with the selection. This third selfing will result in the 65%, 34% and 1% formula and will have become very uniform as to all other plant and fruit characters if the work has been well done.
In handling the seedlings of the third generation of progeny that result from enforced selfing of an hermaphrodite strain a different technique must be used. The seedlings of the third selfed generation will show a Mendalian formula of 65% bearing hermaphrodite, 35% female and 1% male. This is a fixed Mendalian formula that results from peculiarities in the sex chromozome and are not yet entirely understood. There can no longer be any question about the results, however. No amount of further selfing and selection after the third selfed generation will change this formula. There has been a lot of argument about the 1% male plants in this formula. The fact remains that they are always there. Geneticists insist that there must be an error but 1% males always appear and until the obscurity is cleared up they will have to stay on that basis whether they jibe with the strict theory of genetics or not.
If the third selfed generation of hermaphrodite seedlings is subjected to selfing not only will there be no change in the 65%-34%-l% formula in the resulting generation of seedlings but difficulties will be encountered in the way of off type flowers that will result in off type fruit of no value. This peculiarity is the source of the long time argument over the bearing habits of the type hermaphrodite.
There have always been two schools of thought in the breeding of papaya. By far the largest group were those people who attempted to, by continuous selection, get a uniform type of fruit from plants of female character and the use of the so-called male plant as a source of pollen. This group have always claimed that the female plants were far and away the best producers of fruit. The other group have been in the past followers of the De Candole theory that continuous selfing of selected hermaphrodites would result in pure strains of hermaphrodites that were desirable. The difficulty has been that it never did but these people have always taken refuge in the statement that the fruit of the type hermaphrodite was of better character than that of the female plants. Both groups have had some force to their arguments. Female plants are on the whole better producers of fruit quantity than hermaphrodite plants. The fruit is just the same not of
a character suited to the demands of the trade in the States. The fruit of the hermaphrodite plants is apt to be of good character but there has always been this problem of ofF type flowers being produced in increasing quantities as generation succeeded generation.
It seems now that a compromise can be reached in this matter. There are two routes open and neither one has been carried far enough to establish it as the best one. Roth start with a selected single hermaphrodite plant of desirable characteristics. The first three generations are arrived at by enforced selfing of the selected plant and its identical hermaphrodite seedlings in the two successive generations.
The seedlings of the third selfed generation should be subjected to the same rigid selection, for first hermaphrodite character and then for their resemblance to the original selected ancestor and the selected seedlings set out in the field. In this generation, however, instead of sticking strictly to the hermaphrodite seedlings there should be at least ten selected female seedlings that are full sisters to the hermaphrodite seedlings in the field. In this fourth generation these female plants must be the source of the seed. The seed from each female should kept separate, and it is better to keep the seed from each melon separate but identified so that the parent plant is known. It is well to save a large excess of seed and plant plenty of it in the seed beds, because this will upset the seedling formula to some extent.
To get plants to set in the field out of this generation, use only the hermaphrodite seedlings, as producers of fruit. If four seedlings are set in each hill there will usually be at least one hermaphrodite out of the lot and that is the plant to use to produce the fruit crop.
At this point there are two possibilities. One is to continue to plant in each planting each year a few female plants that are full sisters to the hermaphrodite seedlings that make up the planting and continue in each generation to lake all seed from the female plants using only the her maphroditc seedlings arrived at in this way to produce the crop of fruit.
The other possibility is to take seed from the female plants in one generation and then self the hermaphrodite seedlings of selected character for three generations. The known facts behind all this are that in using pollen from the selected hermaphrodite plants onto a female that is a full sister to them there will be little or no upset in the
plant and fruit characters other than sex. Furthermore, this intra-family cross will rehabilitate the bearing capacity of the hermaphrodite seedlings of the strain by preventing the appearance of the oft* type flowers that would otherwise become a more serious factor in each succeeding generation after the third.
It is settled that in the continuing the breeding of hermaphrodite strains of papaya it is necessary to cross out to a female plant in every fourth generation, and if a plant is used that is female and a full sister of the same superficial characters, other than sex, as the hermaphrodite strain there will be the least possible upset of all characters.
In the matter of pollen transfer the breeder can make this operation just as easy or complicated as he wants. The Blue Stem and succeeding Blue Solo strains that have been on the market in Florida for some years were arrived at by simply planting a few female plants of desirable characters other than sex with a lot of hermaphrodite seedlings of selected character then growing large quantities of seedlings from seed taken from the fruit of the best of the females. In the selection that follows only the hermaphrodite seedlings are used as producers of fruit. It is possible to select a particular female parent and a particular hermaphrodite parent and transfer pollen between them by any one of several different methods in hopes that the proper selection has been made.
A-SEXUAL PROPAGATION OF PAPAYA
There is nothing new about efforts to propagate papaya by other means than by raising seedlings. Work along this line has been attempted from time to time for more than a hundred years. The thing that is new is that there has now been some measure of success along two different lines, that is the grafting of papaya and the rooting of cuttings.
Credit should be given to Mr. Flood of Moody Lake near Frostproof, Florida, for discovering a workable method of grafting papaya. Many people in Florida all the way back to Edward Simmonds at the old Bricked Avenue Garden in Miami have grafted papaya, but there was always a criticism of the methods they used in that they did not get a good bond that would stand up in a wind after there was a load of fruit on the plant.
All of the early attempts to graft papaya followed the conventional pattern in grafting other plants. They were
essentially soft tissue grafts. That is a soft tissue terminal bud from a proven plant was set into soft tissue at the top of a seedling three to four feet high. It can be done, and the graft will grow and put on fruit. The difficulties are purely mechanical. The bond is too far up the plant stem and is never strong enough to stand a load of fruit and a wind at the same time.
Mr. Flood went far afield from the conventional methods of grafting in that he made no effort to match up the cambium layers or to use stock and grafting material that were in the same stage of growth.
Any type of a-sexual propagation depends on two things, the possession of individual plants that have been proven to have desirable characters to transmit to grafted stock and the ability on the part of those proven individuals to produce an abundance of grafting material. In the case of papaya the first of these factors depends on the ability to produce by breeding continuously a few plants of the desired pattern of characters. This is not a simple enterprise, but it is a lot less difficult than the situation of the past in which all the plants to make a crop had to be produced as seedlings. The second factor at the first glance looks rather difficult. The plant sucker is the only usable plant material in the grafting of papaya and most papaya plants produce very few suckers if left to follow their own bent. It is possible to induce papaya plants to make many suckers after the first year of their life by a methodical system of cutting the terminals off.
PREPARATION OF GRAFTS
After a plant has made and ripened about two thirds of its first set of fruit, a point that is usually reached at about fourteen months after setting in the field, the terminal bud should be removed. To do this take a sharp knife and cut out the terminal in the crown of the plant where it is not more than one inch in diameter. Care should be taken not to injure the leaf stems around the bud. It is necessary to have the crown go on and develop all the leaves that remain, even the smallest, into full grown leaves to support the growth of the plant. The plant should be examined every week and any buds that start on the upper two feet of the plant stem should be cut off just as the terminal was.
The point here is that there is a force called terminal dominance within the plant that tends as long as there is
a growing bud in the top of the plant to direct all the energies of the plant toward growth at the top of the plant. This tendency is not easily upset and the plant will for a time attempt to re-establish a growing bud in the top. Once this tendency is overcome there will be a tendency for dormant buds all up and down the plant stem to start and result in the growing of a considerable crop of suckers. These suckers will take several months to get to the size and condition of growth that is necessary to make them useful as grafting material. This (its the conditions in Florida very well. If the plant has its terminal bud removed in March when the first crop of fruit is usually drawing to a close then the first suckers will be ready late in June or early in July.
Suckers should be picked out and used for grafting material more on a basis of condition of growth than on their size. Almost any size from that of a lead pencil to a little over an inch in diameter will do. They should, however, be fairly hard at the point at which they are cut and there should be at least four or five inches of the sucker left on the plant so that the stump of the sucker left behind will have a number of buds that will start readily and make more suckers. If this is well handled there will be an increasing crop of suckers from the plant every time a lot of suckers is removed.
Suckers will be in the right condition to use at anything between one and two feet long. Here again the length of the sucker does not seem to be as important as its condition of growth. It must bave hardened tissue at the point at which it is cut. The length of the part of the sucker removed to use as grafting material does not seem to be very important with the reservation that if they are too long wind exerts too much pressure against them and interferes with their making a bond. Eight to ten inches long is about right, but they can be shorter or longer if their condition of growth demands.
In taking suckers from a plant not more than half of the suckers should be taken at any one time so that the leaves on the i-emainder will support the growth of the plant. The tops of the remaining suckers can be harvested as soon as the buds on the stumps of the suckers first harvested have started a good growth. By alternating in this way half of the sucker tops can be harvested about every month or six weeks in the rapidly growing season. A plant that goes into the winter season with a lot of suckers on it will have to carry them in storage 'til the next spring.
In taking suckers from the plant use a very sharp knife and trim off all but the four or five smallest bud leaves immediately so as to cut down the tendency of the graft to wilt. Wrap each graft separately in a piece of wet paper large enough to completely cover it up. Cover the wrapped grafts in a box that will protect them from wind and sun until they can be set. Until we know more about this it would be best to take only about ten grafts at a time and set them immediately. Then get another lot. The time tolerance off of the plant for this sort of material is known to be very short. Just how short is not yet known.
To produce seed'ing stock in which to set grafts plant young seedlings of almost any vigorous papaya strain in a nursery where the plants can be kept growing in vigorous condition all the time. The soil of the nursery must be kept rich and well watered. After the setting of grafts commences water should be put on the ground but not on the plants. In the nurseiy plants should be one foot apart in the row and the rows three feet apart.
The particular seedling into which to set a particular graft is ruled by the size of the base of the sucker. The seedlings should be cut off at from five to ten inches above ground just at the top of the tapered swelling at the base of the plant. At this point the plant should be three to four times the diameter of the base of the sucker that is to be set into it.
In preparing the seedling for the graft; first, cut off the top at the proper point so as to leave a fiat topped stump; second, with a sharp heavy butcher knife make a cut straight down into the top of the stump about half way between the center of the stump and its outside perimeter; third, push the knife straight down with both hands until it is well started and then sharpen the graft with a bevel that is long and straight on both sides: fourth, be sure that the cut in the stump is deeper than the cut faces of the bevel by about twice the diameter of the cutting at its base; fifth, remove the heavy knife from the stump and push the cutting down into the cut until its lower sharpened edge hits the bottom of the cut in the stump.
These grafts MUST NOT BE WRAPPED and they seldom not need tying. If it looks as though the pressure of pushing the cutting into the stump would not hold it tight enough then several ties with soft string can be made but no wrapping material should close up the cut; it must be open to the air. On the graft just above the top of the stump put a small skirt of paper, or if can be had water-
20 DEPARTMENT OP AGRICULTURE
proof cellophane is best. This skirt serves no purpose except to keep rain out of the cut and cellophane seems to work best, because it lets the sunlight in. If the grafts are tied they must be watched every day and the string.! cut with a razor blade as soon as they show signs of cutting into the growing stump.
ROOTING OF CUTTINGS FROM PAPAYA PLANTS
This is an enterprise of promise, but one that cannot be said to have a worked-out technique. Cuttings have been rooted with both indole buteric acid and napthalene acetic acid. The percentage of cuttings that rooted has never gone above 12 per cent. This would seem to indicate that cuttings can be rooted, but that there is still something to be done about the technique. No bearing plants have been yet produced from cuttings, but the 12 per cent return in rooted cuttings was quite uniform over a number of experimental batches. The work was interrupted by a number of things, the war condition among the rest.
Suckers to be used for rooting should be cut off flat against the parent plant, trimmed and wrapped as for grafting and taken indoors right away. There is a bulbous base on all of these suckers next to the parent plant. Before putting them in the root stimulating solution this bulb should be trimmed away just above its top. The cut should be so made as to leave the sucker with a flat base. Two crossed cut at right angles to each other should be made upward into the cutting from the base. The cuttings should be tied loosely in bundles so that they would stand up on the bases of the cuttings and the bundles stood in the stimulating solution for twenty-four hours. The nearer it is possible to get the cuttings into the solution within an hour of the time they are cut from the plant the better will be the results.
The solution should be one to twenty-five thousand of either indole buteric acid or napthlene acetic acid. This can readily be made up from a standard 2 per cent solution.
A-sexual propagation whether by the rooting of cuttings or by the grafting method should result in the stabilizing of the papaya industry and enable it to go ahead on a much better basis. The rooting of cuttings will have to be much better worked out at some future date.
The production of grafted plants in large quantities presents difficulties both in the matter of the breeding of the plants from which the grafting material must come and in the necessities of the nursery enterprises that are going to be hard for the average grower to handle. It is to be hoped that some commercial outfit, preferably in the nurseiy business already, will take hold of this and see that the growers of the state are supplied with grafted plants of suitable character to establish the papaya as one of the big enterprises of the fruit trade. Florida has some very distinct advantages that do not exist in other states as a location for a large papaya industry. The ready cash market in the tourist trade each winter is the number one item in this line. The climate and the closeness to the northern markets arc also factors in Florida's favor.
The papaya grower in Florida should never lose sight of the fact that he is in a highly specialized enterprise. There are a number of reasons. The culture of papaya is expensive figured on a per acre basis, because this nlant must be regarded as crowded out of its natural range here. The only reason for growing papaya in Florida is the very high prices that can be had for papaya as a fresh fruit in the States. Papaya can be grown in Southern Mexico for about $4.00 a ton and there is nothing to it, because that is all they are worth there. There are penalties to pay in the growing of papaya in Florida, but if it is well done they do not mean anything. Just the same, eternal vigilance is the price of existence and intelligent application to the problems the price of success.
There is such wide variation in climate and physical conditions over that part of Florida that can be adapted to papaya culture practices that a text can only indicate the general lines along which cultural practices should go and the matter of adapting this crop to the different districts must be, in the long run, up to the grower wdio has the persistence, energy and intelligence to make the skeleton fit his locality.
Over most of Florida cold, as expressed in freezing temperatures, is the limiting factor in the growing of papaya. The problem is one of economics rather than strictly one of fighting low temperatures. There is a somewhat generalized condition with regard to the growing of papaya. As you go north in the peninsula the soils on the average become better and the growing conditions for papaya are better, but the necessities in the way of frost protection are greater. It is an economical problem for the r-eason
IJ !: I AI i T .M K N T 0 V A GUI 0111 /I" U R15
that tlierc are many places in the state where there are good growing conditions for papaya and they can be protected from low temperatures, but where the cost of frost protection will eat up the growing profits.
It is necessary to determine from the weather records in a given location how many freezing periods are to be expected in a given winter; what the low levels are apt to be and how many total hours it is likely to be necessary to fire to save the plantation. The cost of frost protection must be figured at about 5.00. per acre, per hour for every hour below thirty-two degrees F. The Federal Fruit Frost Service can help a lot in figuring this item.
The knowledge of how best to protect a papaya plantation from frost has advanced a long way in the last few years. Certain orderly procedures have been laid out and proven up by field trails over several seasons and against several types of freezing conditions:
1. A large numebr of small sources of heat arc much more effective than a smaller number of larger sources. There are about four hundred squares to the acre in a papaya plantation. The best protection results from having two hundred fires not much bigger than your hat in half of these squares.
2. The other two hundred squares should have standby fires all laid in them. This will take care of a last minute severe drop in temperatures or a cold that continues longer than is expected.
3. Radiant energy is of more use than heated air in the protection of papaya. For that reason small wood fires are more serviceable than any of tin? orchard healers now on the market. Small wood (ires produce the type of radiant energy needed to a greater degree than do the orchard heaters now on the market.
4. There should be a U. S. Weather Bureau type loovercd instrument shelter as an outside station. This shelter should have at least a good standard frost thermometer in it and it is better to have a registering thermograph in it as well to establish records. This outside station should be far enough outside the plantation not to be affected by the heating and in as near the same physical situation as the plantation as can be arranged. Unless there is some good reason why not, it should he northwest of the northwest corner of the plantation. There must be some ordinary frost thermometers scattered all over the plantation. The local frost service field man can help in determining how many of these and where to place them.
It hardly seems necessary to say that preparation is about three quarters of the battle. Fires should be laid and stock piles of wood ready cut and stacked at the base of the nearest plant should be there by the 15th of November. The type of lighter that is used with the orchard heater is the useful one and these torches should be ready, inspected and a drum of mixed half kerosene or distilate or and half gasoline should be ready by that time with a spigot and funnel.
The old rule was to lire the papaya plantation as soon as ground frost appeared. A great deal of wood has been burned up on that basis that could have been saved for another frost. Papaya plantations have in the last few years gone through nights when there was ground frost and the true air temperature in a standard shelter was thirty-three from 9 P. M. to 8:80 the next morning. No tiring was done and there was no damage.
The papaya farmer must learn to know what the true air temperature is and how it applies to the protection of his plants to the best advantage. It is hard to read the temperatures in a loovered shelter and find them above thirty-two and then go into the plantation where the automobile top is covered in ice and boards are covered with frost and not get a panic. The thing to do is keep moving and watch the lower leaves of the plants. As long as papaya leaves are covered with dew in large drops they are not freezing no matter how much ice is on the steel car top.
There is one infallible test for the beginning of frost damage. When it occurs then you have to fire. When the small papaya about the size of a hens egg begin to sweat white gum then start to lire. Otherwise, fire at flat thirty-two and not above that point. Don't wait below thirty-two if the small fruits do not sweat. Sometimes they will not when the weather has been very dry.
ENTERPRISES IN PREPARATION FOR PLANTING PAPAYA
There are several types of work that should be started months ahead of the date of actual planting of papaya in the field if the plantation is to have the best chance of success.
The papaya does best in the presence of large quantities of organic material in the soil. This applies almost regard-
DEPARTMENT OK AGUKUJI.TUKK
less of the type of soil under consideration. Organic materials can be best applied in the form of well matured compost. Compost is apt to be a rather expensive material because of its bulk and the labor cost of preparation. To justify this expense it is best to use the compost as a carrier of purchased plant foods in whatever form they are used. This makes the composting enterprise serve several purposes. The physical character and moisture retentive ability of the soil are improved. The elliciency of the purchased plant foods will be Increased from two to five times, depending on how badly the particular soil needs organic improvement. The development of a large and effective root system on the plants is promoted.
The preparation of compost should commence a full six months ahead of the time plants are actually set in the field. There should be at least six dry weight tons of material go into the making of the pile for each acre of papaya that are contemplated, and ten tons would be better.
The compost can be made out of almost any organic trash that is available. Crop residues, grass, weeds, old leaves and animal manures will all go into the compost pile and come out usable and useful material. There are many methods of preparaing compost, but the following was worked out in the Province of Indore in India over a long period of time and works very well under almost any condition.
Get the materials that are to make up the pile together in rough piles near a source of water. There should beat least ten per cent of the total material in animal manures, and if it is available the pile could be all animal manures. Put the material down in layers about a foot deep on the ground. When the first layer is down mix animal manures in water at the rate of one bushel of manure to a barrel of water and wet the layer. Use enough barrels of manure water to wet the mass but not to soak it. Particularly, not enough to drain through the mass. Repeat the process layer by layer until the pile is five or six feet high. The greater the mass of the pile the better the results will be. That is, the wider and higher it is within reason, the better the decomposition of the mass will be. The limit is the increasing amount of work that it will take to build the pile as it widens out and goes higher.
Make the piles as flat on top as may be, and the sides as straight up and down as possible. To accomplish this, tramp the outside two feet of each layer as the piles goes up as hard as possible. This will give the pile a dense outer
case of compacted material to hold it straight and cut down loss of moisture at the sides of evaporation. Keep the pile moist by regular light applications of water, but never soak it at any time. This is the hardest single factor to get right in composting.
After about three weeks cut the pile down by taking off thin layers from top to bottom, and repile it in the same manner. In repiling care should be taken that what material was the outside of the pile in the first place shall be inside in the new pile. Continue to keep the pile, just moist until it is taken to the field for use. If possible, the pile should be under a roof. If not it can be thatched with palmetto leaves so that it will shed water from heavy rains. A soaking by rain water at any time except very early stages will leach out a lot of the value of the compost.
FERTILIZERS in COMPOST
There are several methods by which purchased plant foods can be mixed with composted materials and used on the field as mixtures. In a general way all of these methods result in increased efficiency of both the compost and the fertilizers. The efficiency of the composted materials is increased, because the bacteria and fungi that do the work or composting are, in fact, plants; and their work is better done in the presence of added plant foods. The efficiency of the fertilizers is improved because their ingredients are worked over into stable and plant available forms that do not leach out readily.
.mixed fertilizers in compost
Where the grower wants to use ready mixed fertilizers and compost together the mixture should be made when the pile is remade after the first three weeks. The mixture should be made on a basis of 300 pounds of mixed fertilizer to the cubic yard of compost. In calculating this, measure the pile before starting to turn it; because it will swell in turning and give a false picture of the yardage. Any good fertilizer of a formula 4-10-12, with trace elements added will serve the purpose. It is doubly important not to over water or let the compost pile be soaked by a rain after fertilizer is added, because there is so much more to be lost by leaching.
compost plcs FERTILIZER INGREDIENTS
The use of separate fertilizer ingredients in the compost piles arc apt to give better results than the use of mixed
fertilizers. The technique is more involved and, therefore, a little more difficult to handle. The additions of plant foods should still be calculated in terms of 300 pounds of 1-10-12 plus trace elements to the cubic yard of compost.
A cubic yard of finished compost should carry 12 pounds of nitrogen as N., 30 pounds of phosphorus as PjO-., and 36 pounds of potash as K-O. The nitrogen and phosphorus should go into the pile as it is made up for the first time, and the pile left in the first position for two months instead of three weeks. It should bo then cut down and replied, and the potash and trace elements added.
In the nitrogen group urea is the best form for mixing with compost and amophos 11-48-0 next. Sulfate of ammonia should not be used as a source of nitrogen if it can be avoided. If it is used there should be an increase in whatever material is used in the pile to stabilize pit point. In the phosphate group amophos 11-48-0 gives the best results, triple suj>erphosphate next and ordinary superphosphate last. Sulphate of potash magnesium is the best source of potash, largely because papaya are intolerant of the chlorine in muriate, and because the sulphate of potash magnesium carries much needed magnesium in an available form.
Lesser or trace elements copper, maganese, zinc, and aluminum should all be used in the form of sulphates.
In general, all sulphates tend to slow down the biological activities within the compost pile and for that reason should not be added until the first violent activity is past. To add any sulphate in the first stages of composting may result in lengthening out the period of ripening by months.
The time necessary to ripen a compost pile can always be shortened by using some compound that is alkaline or will under biological activity crack to a compound that will result in an alkali. Fine ground limestone has been used a great deal but has the difficulty of tending to lose some of the nitrogen as gaseous ammonia. Dolomite is subject to the same objection. Fine ground rock phosphate of a theoretical 200 mesh to which one hundred pounds of sulphur to the ton have been added works the best. The phosphate does not tend to crack much until the pH goes below 5.0, and the sulphur is a help to the activities of the sulphur using group of bacteria.
The phosphate sulphur mixture should be used at a rate of 200 pounds to the cubic yard at the time the pile is first made up. It can be used up to four hundred pounds to the cubic yard with beneficial results.
FIELD USE OF COMPOST OR LOADED COMPOST
Compost or compost loaded with purchased plant foods should be used rather generously in the preparation of hills before plants are set in them. When it is desirable to use additional plant foods they can best be added by ploughing a furrow alongside the plant rows at about the end of the feeding roots and placing compost opposite the plants in the furrow on each side. The furrow can then be ploughed shut to cover the compost. Successive applications can be made in the same manner with the furrows a little farther away from the plants each time. Fertilizer applications should be calculated on a basis of 300 pounds of 4-10-12 in compost every sixty days for the first year. This will sound like a lot of fertilizer, but it is well to remember that you are expecting this crop to produce twenty tons of fruit within sixteen to eighteen months from the time it is planted. A grapefruit grove will only produce sixteen tons under the best conditions after it is ten years old.
SOIL TYPE DEMANDS OF THE PAPAYA
The papaya can be saicl to be tolerant of a very wide range of soil types, because it will grow and produce on almost any soil type in the peninsula of Florida if cultural practices are varied to suit the soil type.
If there is any such thing as an ideal soil type for the papaya it is a deep, loose, well aerated sandy soil. Such a soil is only a good base on which to build the condition best suited to papaya by chemical adjustment and plant food level adjustment to fit. Such soils exist on the coastal sand ridges, on the off-shore islands, on the Ridge of Central Florida and to some extent in the flat sandy lands of the interior.
In evaluating these soils the big item is the cost of making the necessary soil adjustments and the cost of fighting frost in each particular location.
The rocky lands of south Dade County have long been the location of the largest part of the papaya growing enterprises of the state. Such lands are principally recommended by their comparative freedom from frost and by their proximity to the large cash market for fresh fruit in Miami. They are rather difficult and expensive to adapt to papaya culture but will produce if properly located and treated as large crops of fruit of as good quality as can be grown anywhere in the state.
The marl soils will produce large crops of papaya rather economically, but the fruit is not of top quality; and these soils are hard to protect from overflow under most conditions. The principal thing to recommended them is that the soil is workable and moisture retentive.
The flat pine woods soils will grow good crops of papaya if they can be defended from frost and flooding but are in their very nature hard to defend against both of these serious hazards of papaya crops. The immediate topographical conditions are the only index of their usefulness.
The muck soils cannot be recommended for papaya culture except under special conditions. They are generally hard to defend from water and frost, and the quality of the fruit is apt to good. Muck soils will produce papaya more cheaply than any other soils in Florida when their location and condition is such as to make them usable for the purpose. Muck lands of the custard apple type that are so located that they will not flood are the best bet in this group.
Where hammock soils exist that are defendahle from frost and flood they are among the best soils in the state for papaya.
CHEMICAL CONDITION OF SOILS
In a general way papaya are tolerant of a wide range of chemical condition in the soils on which they will grow. When the matter of getting the best possible crop is under consideration the papaya is much more demanding in chemical condition of soil. Each group of soils and each variation of type within the groups must be evaluated and given specific treatment. If a given soil is too far out of line either way in pH point, corrections will have to be made and the method of correction used will have to fit the particular requirements of the soil to get the best results in quantity and quality of fruit.
Papaya have been grown with some measure of success on soils whose pH point was all the way from 4.5 to 8.3 in Florida. This has been accomplished without the use of chemical correction of the soil. Better and more economical results can always be had by making chemical corrections first. The character of chemical adjustment must be in every case fitted to the peculiarities of the particular soil.
Sandy soils on the whole will require pH correction upward before they are fitted to the growing of papaya. The decision as to what material to use to make the correction
and to what point to correct is not an easy one to make. It is necessary not only to know the pH point but the base exchange capacity before attempting corrections. It takes 150 pounds of fine ground high calcite limestone to the acre to change the pH point one pH when the base exchange capacity is one base exchange.
When a sandy soil has a base exchange canacity of two or below it is not advisable to raise the pH point much above 5.9 to G.2. Most Florida soils of sandy character and on the peninsula have a base exchange capacity of about 1.65 and a pH point of 4.5 to 5.0. The business of determining the base exchange capacity and the pH point then making a calculation of the amount of high calcite to apply is definitely in the province of a soil chemist. There is a further complication in that hijrh calcite and dolomite arc not suited to making the correction for papaya so there is a further calculation necessary to express the necessities in terms of raw rock phosphate, because this is the most suitable material for the purpose.
There is a specific difficulty in making pll corrections on sandy soils of low base exchange with materials like high calcite and dolomite. If enough of these materials are used to insure the desired rise of pH in wet weather there is always the danger that the small amount of base exchange material these soils contain will be over saturated with calcium in periods of dry weather. If this difficulty reaches the point of free calcium in the soil over and above the ability of the base exchange material to take it up then calcium goes into the soil solution and impares the value of the soil solution as a carrier of other plant foods. This in turn accentuates the difficulties of plants due to dry weather so that even a moderate drought will radically cut down the activties of the crop.
Raw rock phosphate ground to 80%, or better, 200 mesh, has a number of points that recommend it for the purpose of making such corrections. Raw rock phosphate (tri-calcium phosnhate) has a rather active tendency to crack at low pH points but slows down as pH rises until at somewhere between 5.9 and 6.2 there is little or no tendency to further cracking. For this reason there is little tendency of this material to carry the calcium saturation of the base exchange material above 80%.
This is not, of course, a fixed point, the greater the base exchange capacity of the soil the higher point of pH it is at which there will slid be active cracking of the raw lock phosphate. This is particularly true in cases where
32 DEPARTMENT OE AGRICULTURE
there has been a temporary rise in base exchange capacity due to the addition of a lot of organic material such as compost. The implication of the use of tri-calciumphos-phate as a soil corrective remains the same, there will almost never be over saturation of the base exchange material as a result of the use of this material.
There is a purely economical recommendation for raw rock phosphate as a soil corrective on thin sandy soils. In cracking due to the activity of soil acids this material furnishes over a period of years enough PjO.-, to pay for its application and the material. The stabilization of pH is a no cost by-product.
To lay out a specific method, one ton of raw rock phosphate is roughly equivalent to 750 pounds of high calcite limestone in potential alkalinity. One ton of raw rock phosphate is therefore almost exactly the correct application on an acre of the thin sandy soils of the Ridge where the base exchange capacity is 1.65. The correct dosage can be figured either way from that.
The cracking of raw rock phosphate is almost entirely in the soil, the result of biological activity. The end product contributes to biological activity. There is then a much improved biological activity where raw rock phosphate is used as a foil corrective. This increase in biological activity can further be speeded up by mixing one hundred pounds of sulfur with each ton of raw rock before applying it to the soil.
On soils of naturally high pH such as the marl soils and the rocky soils of Dade and other South Florida counties it is not economically possible to change the pH points so as to bring them within the bounds of theoretical preference. On such soils there is only one out, and that is to grow the crop in the presence of large quantities of organic material. Composted material that is ripe should be used in the soil, and to carry all purchased plant foods and raw organic material should be used as a mulch on the soil surface partly to retain moisture and partly to create a zone of lowered pH between the surface of the soil and the mulch. In this zone the feeding roots of the crop will find it much easier to work.
In the determination of the chemical condition of the soil before correction and in the laying out of the methods for making corrections, the papaya grower has no alternative but to make use of the soil chemist. That does not mean for one minute that the grower should dump his soil chemistry problems in the lap of the soil chemist and
then assume that his own responsibility in the matter is ended. The soil chemist is human; he is also a specialist and like all specialists, is prone to look on all problems in the light of his specialty, soil chemistry. The grower of papaya has many interlocking problems and soil chemistry is only one of them. The successful grower of papaya will have to evaluate the results of the soil chemist in terms of his whole papaya production problem.
PLANT FOOD REQUIREMENTS
In supplying plant foods to a crop of papaya it is necessary to keep in mind that this crop is expected to produce a vegetative growth and fruit crop of a size that is not equaled by a grapefruit grove until its tenth year. The papaya has to do this in sixteen to eighteen months. The answer in plant food supply is not simple. Particularly, it is not just a matter of pouring on a lot of fertilizer; because few Florida soils are capable of holding the necessary plant foods for a papaya crop without specialized treatment.
There are several roads to follow. By far the simplest procedure is to supply all plant foods in the form of compost loaded with fertilizer or fertilizer ingredients. Another road is the use of mixed fertilizers applied at very short intervals. This is only apt to work well when there is regular watering in the form of overhead irrigation. The difficulty with this method is that fertilizers are apt to pile up in the soil as raw unassimilated fertilizer salts in dry periods and burn the crop seriously when rain comes. Another method is to apply all plant foods in the form of soluble fertilizers in the irrigation water. No one of these methods can be kept in line with the necessities of the crop and away from dangerous concentrations of fertilizer salts without regular soil analyses at least every three months by a competent soil chemist. The grower should keep and use a quick soil test outfit but should evaluate his results in terms of their relationship to the quantitative analyses by the chemist. It will take about a year to establish this picture in the mind of the grower, but once the methods are properly evaluated in terms of each other the grower can check his soil, chemical and plant food situation at regular and short intervals with the results of the chemist as a master check every three months. There is nothing in this that will relieve the grower of the necessity of having quantitative analyses made by a chemist at intervals.
DEPARTMENT OF AGRICTT/ITRE
The quick test is only an approximate check that the grower can use to save fees.
Regardless of how plant foods are applied there is a pattern of specific plant food levels that should show up in each analysis by the soil chemist.
There should be at all times a showing of 2 pounds of nitrate nitrogen to the acre in excess of plant use. This is a figure for nitrate nitrogen in equilibrium over plant use and should be backed up by a total nitrogen complex of nearly 3,000 pounds to the acre. To give an example: The sandy soils of the Ridge as virgin soils shows a 0 nitrate nitrogen and a total nitrogen complex of something above 700 pounds to the acre. By making applications of about 200 pounds of urea at a time spaced at from six to eight weeks intervals it will take over a year to raise the total nitrogen to 3,000 pounds to the acre and the nitrate nitrogen to two pounds to the acre.
This nitrogen build up should start soon enough so that the third application is made about a month after the plants are set. The grower must keep in mind that this figure of two pounds of nitrate nitrogen to the acre is one of surplus of nitrate nitrogen in equilibrium over plant use. In the papaya plantation after the sixth month the use of nitrogen is enormous and the two pounds represents only what is left over after the plants have taken what they wanted of what was cracked out of the total nitrogen complex. The necessity for watching the total nitrogen level is evident.
The average sandy soil on the Ridge will show, as a virgin soil, thirty to forty pounds to the acre of plant available phosphorus. This must be gradually raised until at the time the first fruit begins to ripen it has reached 800 pounds of plant available phosphorus. It is entirely possible to use nitrogen enough to grow a twenty ton crop of papaya and have it absciss and fall on the ground at maturity of the fruit but unripe. This peculiarity is accentuated in the cold months in Florida and is more apt to occur the farther north in the State the crop is located.
Superphosphate should be applied first a ton to the acre as soon as the land is cleared and then again after a check about eight weeks later. This process should be repeated as often as is necessary to get the 800 pound level.
Potash need not be applied until the planting of the crop but must reach a level of 150 pounds to the acre as Ka0
by the time the crop is six months old. Potash is best applied as sulfate or sulfate of potash magnesium.
It becomes evident that the plant food levels discussed above are going to be hard to attain on most Florida soils and that the best efforts of both the soil chemist and the grower are going to be needed to get and maintain the levels required. The grower must not think that once these levels are reached the battle is over, quite the contrary, they must be maintained as long as the crop continues to grow.
PAPAYA NURSERY STOCK
The production of papaya nursery stock has, in the past, been a matter of raising the best seedlings possible from the best seed stock available; and that has been the largest single factor in holding back an industry that should have gone ahead much faster. The long time difficulty has been that even with the best efforts of both papaya breeders and growers the results from seedling plants as nursery stock left much to be desired.
It will take time but this should change rapidly from here out, because of the ability to graft plants for the production of crops of uniform character.
SEED FLAT AND POTTING SOIL
Potting soil for papaya should be loose, well areatcd, coarse textured soil made up of largely sand and organic material with plenty of phosphorous and not too much of either nitrogen or potash. Potting soil should be mixed as long as possible in advance so that the materials get a chance to cure together. The last step before using should he to sterilize the soil for nematodes with formaldehydes, formaldehyde dust of sulfocide.
There are a number of roads to follow in developing papaya plants to set in the field. They all will be given as they all have their place and recommend themselves for particular conditions. The commonest source of difficulty in handling papaya plants when moving them to the field results from too much petting and producing plants that are too soft to take the rigors of the field condition. It must be remembered that it is much easier to harden plants off in the nursery than it is to give the whole field conditions that soft plants will tolerate.
SEED FLAT ROW METHOD
This is the commonest first step in the growing of papaya plants. Flats are filled level full with potting soil through
a screen. This results in the soil being light and fluffy in the flat. The surface should Ik* struck off with a straight-edged board. Next, take a small stick the length of the width of the flat. This stick is one-half inch thick and three-quarters of an inch wide. Press the stick down edgewise into the surface of the soil in the flat until it is level with the surface. Do this about two and a half inches from one side of the flat and repeat it every two and a hall-inches all the way across the surface of the flat. This results in a series of furrows in the surface of the soil that are as long as the flat is wide, three-quarters of an inch deep and one-half inch wide.
Shake seed into these furrows until they almost touch each other the whole length of the furrow. Next shake a little more potting soil over the seed and with a Hat block of wood press the whole surface of the flat firm. If the routine has been properly followed the seed will be covered about one quarter of an inch deep with firm soil. Wet the soil rather heavily this first time. Next cover the surface of the soil with six or eight thicknesses of wet paper, The paper should be so cut as to fit down snugly inside the flat to the surface of the soil all over. After the tenth day lift one corner of the paper on each flat every morning, and as soon as the sprouting of the seeds begins to crack the ground take oft the paper and give the flat the second good watering. These two waterings should be enough to get the seed up, but care will be necessary not to water too often or to let the flat dry out. In watering papaya it is always better to water well and then not water for several days. This applies just as well after the plants arc up and growing.
As soon as the plants have two leaves besides the? seed leaves they should be pricked out of the flat and put either in other flats at the rate of thirty-two to the standard seed flat or into pots. From the time the seed come up until they are moved up the next step, more papaya plants are lost than at any other time. They damp-off very easily and one of the propietary materials to prevent damp-off should be used.
This is recommended as the best system for starting papaya seedlings, because it avoids crowding and helps to control damp-off without having to dose the soil while the seedlings are growing.
Fill a seed fiat with soil through a screen as before. Take a block of wood and firm the surface of the soil well. Water
tlie soil rather heavily. Next, scatter seed on the surface of the soil thickly. Ten times as much seed as in the furrow method. Do not press the seed into the soil or cover with soil. Cover the seed with a number of sheets of wet paper and finally with a thickness of wet burlap. Lift a corner of the paper on the eighth day and if any of the seed show white lines where the seed coat has cracked it is time to begin pricking them out in another flat at the rate of thirty-two to the standard flat or in pots.
After all the cracked seed have been pricked out to a new container on the first day, recover the seed and wet the cover. Do not wet until after the cover of paper has been replaced. Each day thereafter take out the cracked seed and pot it up until no more crack.
Field seed beds are not generally recommended for planting seed directly, because it is too hard to maintain the conditions that are necessary to get results with papaya.
nurseries in the open
As soon as plants have six leaves they can be set out in beds that have been well prepared in the open. The plants should be set in rows about eight inches apart, and tli plants about three inches in the row. The bed should be covered for a few days until they are established, and then the shade gradually reduced until they are out in the open. The plants can stay in these open ground beds until they arc ready to go into the field.
If the plants are to be grafted they should be put: into nursery rows that are three feet apart and the plants one foot apart in the row where they can stay until grafted and then be moved to the field.
MO I ST URE REQUIRE M E N TS
The papaya is with a certain amount of justice listed as a drought resistant crop, particularly, in Hawaii. There are a number of reasons why it is unwise to let this crop go dry in Florida. The principal one is that the crop is wanted at a particular time, and if it goes dry for long the calendar is badly upset. It is possible in South Florida to set papaya plants in the field almost any day in the year, and if growing conditions are maintained to count ahead eight months and say that day we will pick papaya. This is not true
farther north, because as you go north in the peninsula the growing of papaya becomes more and more a seasonal enterprise. The size of the eventual crop in any one year is bound to be affected adversely if the papaya crops is allowed to go dry for very long. The quality of the crop is always lowered if any very long dry period is allowed to check the crop for long in any one season. In this last difficulty, if the plants come through the drouth, the crops of succeeding seasons will not be affected.
The papaya is peculiar in its water needs, in that it will make use of very large quantities of water if supplied regularly in small doses but requires perfect drainage. This plant will not tolerate for one twenty-four hour period the flooding or even the saturation of the land on which it grows. This makes it necessary to plant the papaya on high well drained soil, and then irrigate, if the best results are to be had. This is particularly true under Florida conditions, because we do not have moisture retentive soils. It is perfectly safe to say that whether irrigation is looked at as one of the physical problems or in the light of probable financial success it is a necessity in some form in the Florida papaya plantation.
Many types of irrigation have been used to grow papaya in Florida. The ideal thing is the permanent overhead system, but it is costly and adds to the financial difficulty of getting started with a crop that it, in its very nature, a costly one.
There arc a number of portable line types of overhead irrigation. They usually consist of a well in the center of the tract; a small pump; a distribution line that will reach from the center line of the tract one way out to the border; and a conductor line that will reach the other way. With this rig it is possible to water the whole tract by repeated settings,of the two lines. A four acre unit with a well in the center can be set up quite economically and makes all the papaya planting that one man can handle without a lot of help.
The slip joint pie system with perferated distribution lines and solid conductor lines will handle just as large tracts as it is possible to handle the other operations on. The slip joint system is the most economical for large enterprises.
In applying irrigation water the character of the land must be considered. There is a large difference in the ability
of soils to take up water. In general, it takes at least an inch of water to do a crop any good. The factor that must not be lost sight of is that an inch of water is nearly twenty-seven thousand gallons. Think about that when you plan to carry water to an acre of papaya.
Some soils will take up an inch of water in thirty minutes, but very few of them. It is much better to have the irrigation set-up such that it takes two hours to get an inch of water. It is inspiring to see water sloshing all over the place in dry weather but not very effective.
IRRIGATION AS AN AID TO FERTILIZATION
If irrigation equipment is properly planned it can be a great help in fertilization and furnishes the most economical method for fertilizer distribution on an established papaya plantation. To take advantage of the irrigation system as a means of fertilizer distribution it is necessary to have the soil corrections made, the organic content of the soil high, the plant food levels adjusted and established in advance and to be able to check chemical condition and plant food levels regularly by soil analyses.
The water soluble fertilizers that are usually spoken of as high analysis fertilizers are the most useful for this purpose. Water soluble fertilizer ingredients such as urea, amophos, sulfate of ammonia, sulfate of potash, magnesium and trace elements in the form of sulfates are also useful. Let me stress again the organic content of the soil must be high by additions at regular intervals of well ripened compost. There is a tendency with this system of fertilization for the organic content of the soil to be rapidly eaten up.
The mechanical equipment necessary depends entirely on the source of water. If the irrigation water is coming out of a well it is necessary to have located at the well a tank of about 80 gallons capacity for each acre that is to be irrigated at one set of the system. The tank should be of wood. Metal will not serve the purpose. There should be a small bleeder line from the tank to the suction side of the pump. Fertilizer calculated for the size of the piece of land to. be irrigated in the particular set is dissolved in the tank. Run the pump until the set is good and wet and then open the valve between the pump and the tank. The fertilizer solution will be sucked out and mixed in the pump then passed on to the field in the entire mass of the irrigation water.
In cases where water is pumped out of a lake or canal some arrangement must be made around the foot valve to confine the fertilizer to some extent, and the dry fertilizer can simply be dumped slowly around the foot valve. The travel of water is all to the foot valve so it will all go into the sytem and be distributed in the same manner.
This is the ideal method for distributing plant foods in the form of fertilizer. It gets even distribution on almost a square inch basis. It avoids all the old difficulties of fertilizer throwing. It particularly enables the farmer to apply all the fertilizer himself and, therefore, to know-just how much and where. This is a very important item as fertilizer is the highest single item of cost in growing papaya. Further, by no other method is it possible to get plant foods to the plants in as readily available a form or keep as accurate a check on the plant food situation.
There is no such thing as a frost free location where papaya can be grown in Florida. Frost is the commonest source of loss to the papaya grower. An understanding of what is needed in the particular location and a workable method of frost protection are two things that are absolutely essential to the papaya grower in Florida. The Frost Protection Service and, particularly the local field man of the service can be of great assistance to the papaya grower in evaluating his problem and working out a solution.
Frost protection is first a problem in economics and then a problem in physical facts. It is physically possible to protect papaya from frost almost anywhere in Florida, but the protection would cost so much in a lot of locations there would be no profits. This problem is aggravated, in a way, by the fact that generally speaking the further north you go in the peninsula the better soils become available for the growing of papaya.
Then frost is not the only cold induced problem connected with the growing of papaya for profit. There is a chronic problem in California that has defeated all efforts to grow papaya out-of-doors in spite of the fact that they have frostless districts. If the soil on which papaya are growing becomes cold below a certain point and then gets wet all of the feeding roots will rot off and most of the secondary roots will disapear. This happened on the Ridge in the spring of 1940. The plants stood in the ground with nothing but the carrot like tap root to hold them up for several weeks. Very few of the plants died, and when the
easily jump over the United States Capitol building in Washington. And the walls of jails would have to be a quarter of a mile high. Fleas may easily jump a distance of 12 to 14 inches in one jump, and they may jump as high as 7 or 8 inches.
METHODS OF CONTROL
It is evident that in ridding a house of pests, the first thing to be done is to remove the source of the pests. In the case of fleas this source will nearly always be found to be a cat, dog, or other pet. Such pets should not be allowed to stay in the house, for if they are, sooner or later the house will become infested with fleas. Pets should be provided with mats to sleep on, and the mats should be cleaned out at least once a week. The pets themselves should be kept as clean as possible by washing them in a solution of creolin made by adding two to four teaspoons of creolin to each gallon of water, or by frequently dousing them with powdered pyrethrum. When using this latter method, the fleas that fall off should be caught on a paper or cloth and burned. Another method of ridding pets of fleas is to bathe them in certain miscible oils or creosote dips.
The problem of ridding a house of fleas is much harder than that of ridding pets of them. One of the best ways to treat an infested house is to fumigate it with hydrocyanic acid gas. The fumigation should be started about 8 o'clock P. M., and left until the next morning. The windows should be opened from the outside, and the house should not be entered for at least two hours after it has been opened up. Burning sulphur may also be used for fumigation instead of cyanide. Both of these methods are injurious to paint and furniture.
Another method of killing is to sprinkle napthalene flakes on the floor of the rooms and close all the doors tightly for several hours. This is a very excellent way.
The author has achieved excellent results by spraying creosote clip over an area infested with fleas. This method was used under a house to rid the ground of them, and might be harmful to furniture if used to any extent on the inside.
In ridding a house of fleas it may be necessary to take up all the carpets, and thoroughly wash all the floor space with hot water and soap. This is for the purpose of getting them out of the cracks of the floor, and other places where they might be hiding. In extreme cases it may be necessary to replace the
carpets with rugs. There is no better place for the larvae of fleas to develop than in the thick matting of a carpet. It not only affords protection to the insect during its various stages of development, but it will probably contain enough dust containing organic matter for the insects to feed upon.
Sometimes fleas may be driven out by the persistent use of pyrethrum. The material should be sifted in the carpets, along the base boards, and in any cracks between boards of the floor. However, in some cases this treatment has utterly failed.
Another method which has been used successfully is to sprinkle benzene on the carpets and floor. However, in doing this it should be remembered that benzene is highly inflammable, and care should be taken not to get it near a fire.
Even fly paper has been successfully used in ridding a large room of fleas. In one instance the fly paper was tied around a man's legs, and as he walked about the room hundreds of fleas became stuck fast as they jumped on the paper.
It has been said that oil of pennyroyal will drive fleas out of a room if it is sprayed thoroughly therein.
There is probably no household pest known that is more annoying and more dangerous to man than the common house fly. To begin with, the fly is filthy. He much prefers to be in a pile of manure or other filthy place than in a clean place. Alsothe fly has various habits and features about him that make him very adapted to carrying various kinds of bacteria. For example: when a fly lights on a surface he immediately sets to work with his proboscis to rub the surface. When he has rubbed it slightly rough, and has got some of the surface into solution with his saliva, he proceeds to suck it up into his body. Thus any germs which happen to be on the surface would be sucked into his body also. These germs are more than likely to be deposited on the next surface which the fly lights on. In many cases he may light on food, dishes, various kitchen and eating utensils, etc. Consequently, the fly is excellently adapted to carrying disease germs in his alimentary canal. In addition to this he is provided with microscopic hairs on the bottoms of his feet and on the sides of his legs. These hairs, especially the ones on the feet, are constantly kept sticky with a solution excreted by the fly for the purpose of aiding him to walk up-
side down without falling. Unfortunately, also, it is very effective in catching and holding disease germs with which it may come in contact.
The disturbing thing about the fly is that he can carry so many different kinds of disease germs. It is known to carry the germs which cause typhoid fever, tuberculosis, cholera, dysentery, infantile diarrhea, leprosy anthrax, tapeworms, hookworms, roundworms, whipworms, opthalmia, yaws, erysipelas, gonorrhea, septicaemia, abscesses and gangrene.
It is the fly's unending curiosity that makes him so great a disease carrier. He seems actually to get into everything. This is why he is so likely to come in contact with such a great variety of germs.
METHODS OF CONTROL
The best way to get rid of flies is not to allow any more to hatch. The favorite place for flies to lay their eggs is in manure (preferably horse manure). For this reason all stables and barns should be kept as clean as possible. Where they have floors other than dirt they should be scrubbed at least once a week. If a pile of manure is left standing for over a week in the summer time, it may, on some occasions, be found to be full of the larvae of flies (maggots). In a short time these larvae become pupa and will eventually become adult flies. It has been thought in the past that flies in the larvae stage would eat up enough filth to make up for any damage they might do when they become adults. However since is has been found that flies carry so many disease germs this theory has been proven to be wrong many, many times.
Another precaution which should be taken against flies is that all dwelling houses should be screened. Of course this will not destroy any flies, but at least it will keep them from entering the house and going about at will.
In cases where fly paper is used it is better to use sticky paper than poisoned paper. There is always the danger that poisoned paper will come in contact with something that it should not, and sticky paper is just as effective. This paper should be hung in strips where the flies are most numerous, and any fly that touches it will become stuck fast. When the paper is covered with flies it should be disposed of and replaced by fresh paper.
There are, of course, various patented insecticides which may be effective against flies. But in most cases it will be found they act as repellents rather than destructives.
It is also true that various kinds of devices have been made for the trapping of flies. This may prove effective when used over a garbage can or other small place frequented by flies, but usually it will prove very futile since so many more flies can be hatched. A pound of manure can produce about 1.200 flies, and this is considerably more than a trap could catch in a long time.
Another important item in controlling flies is to do away with open privies wherever it is possible. These provide very excellent breeding places for flies and are also more than likely to contain some disease germs. If it is not possible to have adequate sewerage disposal as in the cities, the privy should be placed over a creek or river. If this is not possible it should be built away from the house, and if the household is dependent on a well for its water supply the privy should not be near this well because it will contaminate the water. Moreover, if a privy must be built away from running water, it should be disinfected regularly with some disinfectant such as lime or chloride of lime. The disinfectant should be provided in a convenient box, and a paddle or small scoop or large spoon should accompany it so that some of the disinfectant can be scooped into the pit every day.
It is important that everyone should know how to prevent and kill mosquitoes. For these small insects are the only carriers of the germs which cause four very serious diseases. In addition to being disease carriers they can inflict a very painful bite. Of the diseases the mosquito can transmit, the one most dangerous and most familiar to the majority of people is malaria fever (sometimes known is chills and fever). The germ which causes this disease must undergo a certain stage of its development while in the body of the mosquito. The other stages can take place in the human body. Thus we see that if there were no mosquitoes there could be no malaria. To narrow the subject down still more we may say that there would be no malaria if we could stamp out even one species of mosquitothe one known as the malaria mosquito. The other disease transmitted
by mosquitoes, known as yellow fever, filariasis, and dengue or breakbone fever, could in the same way be wiped out if we could rid ourselves of mosquitoes.
There are more than 350 different species of mosquitoes known to exist in North America. The three most common of these types are the Culex (common), Anopheles (malarial), and the Aedes (yellow fever). All mosquitoes pass through a complete metamorphosis, and to do this they must have water that is not in rapid motion; stagnant water is better. With this fact in mind we turn to preventive measures.
METHODS OF CONTROL
Since mosquitoes cannot reach the adult stage without having had water in which to breed, the best method of combating them is to not permit water to stand stagnant. If this water cannot be disposed of, it may be rendered unfit for mosquitoes either by pouring oil on the surface or by using chemicals in dust form, such as paris green or sodium arsenite.
In some cities and towns a mosquito inspection force is maintained by the city government. In such instances every house and lot in the city limits is inspected regularly for the larvae of mosquitoes (wiggle tails). It is also the duty of this force to turn over any receptacle which contains water or which might contain water after a rain. In the case of barrels full of water that have been set aside for use in an emergency such as fire, it the duty of the inspector to see to it that some preventive be placed on the water surface for this purpose. This method of mosquito prevention is indeed very effective when carried out efficiently.
One method of preventing mosquitos on larger bodies of water is by the introduction of top-feeding fish or minnows. These fish will feed on the larvae of the mosquitoes.
Another precaution which should be taken against mosquitoes is the screening of all houses. This should be done carefully and completely, since the mosquitoes are so small that they enter through very small cracks.
Mosquitoes may be cleaned out of a house by means of pyre-thrum sprays, certain commercial oils, or by fumigants. When one must be exposed to mosquito gloves, netting, and repelling oils will prove effective. Of all the mixtures and compounds that have been developed for repelling mosquitoes probably the best one is oil of citronella.
Moths are different from most insects that bother man in that they attack property instead of man himself. There are any number of different kinds of moths, and each species attacks a different kind of property. Some moths feed on clothing and may cause considerable damage in this way. Others feed on certain crops such as grain, grapes, berries, peas, potatoes, etc. Of course it would not be possible to discuss each species of moth which is known, but it is interesting to note that in every case where damage has been done by moths it is the moth in the larval stage that does the damage. It is also interesting to note that practically all moths except the clothing moth are attracted by light. At night hundreds of them may be seen flying around a light bulb if it is possible for them to gain access to it.
METHODS OF CONTROL
Clothes MothClothing that is in daily use is rarely attacked by moths if ever. But when clothes are packed away for a season they are in great danger of an attack by moths if not properly packed. The method which is most commonly in use and which is probably as good as any other for protecting clothes that are packed away is to sprinkle napthalene flakes over the goods at the rate of one pound to 10 cubic feet of space. Clothing should be thoroughly shaken and brushed before it is packed. This may get rid of any moths or eggs that infest it. Another substance that will give complete protection from moths and will kill all stages of insects is para-dichlorobenzine. It is used in the same way as napthalene.
Infested clothes may be freed from moths by fumigation with carbon bisulfide. This also will kill all stages of the insect.
Cedar chests are effective in keeping adult moths out of clothing, and will kill any larvae that hatch out in the clothing, but if larvae are introduced into cedar chests after they have developed to an extent, they will eventually mature into adult moths.
Heating will kill all stages of the moth, and clothes will not be damaged by moths if they are kept in cold storage. (45 degrees F. or colder.)
Other Types of MothThe most effective method of killing moths other than the clothes moth is by spraying. It has been found that spraying with lead arsenate will give almost com-
plete control of this insect. Three pounds of this chemical to 50 gallons of Bordeaux mixture is a very good proportion.
The Silver Fish MothA second kind of moth that is very destructive to books, etc., is called the silver fish moth. This moth has no wings and its body is only about 1/8 of an inch long. Books that are packed away in dark, damp rooms are almost certain to be attacked. This suggests that any valuable books or papers should be stored in light, airy rooms. The frequent use of powdered pyrethrum on the books and on the shelves about them will give added protection. This powder must be renewed often because it loses its strength. In badly infested houses this moth may even attack starched clothes, stiffened silks, and similar fabrics which remain packed away for any length of time. Another way of combating the fish moth is to put a mixture of white arsenic and paste on pieces of cardboard and place them where the moths can easily got to them.
There are countless varieties of weevils that feed on grain and other crops in the field. But, however, since this bulletin deals only with such pests as come in and immediately around the house, these field weevils will not be treated here.
The Granary WeevilThese weevils lay their eggs in a small hole which they make in a grain of wheat, bean or corn. When the egg hatches the young weevil foods on iiinide of the grain. However, they will usually make their appearance in the finished product. They have been found in shredded wheat biscuits, and even on Pullman dining cars, where one pays for the very best quality of food. The corn and bean or pea weevil are the ones that most concern the people of Florida.
The rice weevil is the second one that enters the household. It and the granary weevil are really the only two that come under this classification. As one would suppose it gets its name from the fact that it was first found in rice. The rice weevil is supposed to have originated in India, and from there it has spread all over the world. It is the most harmful of the two that inhabit this country, but it is not as widely distributed as the other.
The rice weevil feeds upon the grains of rice and often invades boxes of crackers, cakes, and other broad-stuffs, and is found in barrels of flour and sacks of meal. In the summer it may remain in the field, but in the winter it will retreat to barns, houses, or any other place where grain is stored.
METHODS OF CONTROL
The most effective method of combating weevils is with carbon bisulfide. This liquid should be used at the rate of two or three pounds to every 1000 cubic feet of space.
A good way to keep weevils from infesting various kinds of seed is to store the seeds in tight dry goods boxes. The boxes should be filled to within 3 or 4 inches of the top. If weevils should infest them they should be treated with carbon bisulfide. CautionNo form of fire whatsoever should be brought near the carbon bisulfide until the fumes have thoroughly dissipated in the surrounding atmosphere.
The best thing to do with any small box of cereal, crackers or other food that has become infested with weevils is to throw it away entirely.
All stages of weevils will be killed if a temperature of about 130 degrees can be maintained for several hours.
(1) DDT, Dichlorodephenyl Trichlor Ethane.
(2) Chlordane, also known as Vesicol 1068. an Octa-Klor.
(3) Hexachlorocyclohexane. also known as Benzenehexa-chloride.
(4) Chlorinated Camphene known as "Hercules 3956" or Toxaphene.
All of these have been tested and proved more or less effective against household insects. Most effective control methods:
Mosquitoes, Ilouseflies: Pyrethrum sprays with DDT.
Bedbugs, Roaches, Lice, Fleas: DDT sprays or powder, Chlordane, Toxaphene.
Clothes Moth: Pyrethrum Sprays, DDT Sprays, Paradichlor-ben/.ene, Naphthalene (Moth Balls), Chlordane.
Ticks, Fleas, Chiggers: DDT Spray or powder, Chlordane.
House Ants: Ant Poisons, DDT Sprays. DDT Powders.
Outside Ants: Ant Poisons, Carbondisulfide. Cyanogen.
Carpet Beetle, Silver Fish: DDT Sprays, Chlordane Sprays.
All of these insecticides are more or less poisonous to man and must be used according to the directions and precautions given by the manufacturer.