by W.R. Beattie, Senior Horticulturist
Division of Fruit and Vegetable Crops and Diseases, Bureau of Plant Industry, May 1938
Watermelons are grown for the market on an extensive scale in about 20 States, the main producing areas being located in the warmer parts of the country, on the light sandy or sandy loam soils.
Watermelons are often grown on new land or in a long-period rotation to avoid serious losses from diseases. Good seed is of great importance in the production of high-class melons for market, and there is great need for the improvement of present methods of seed production.
Careful handling is essential in the loading and shipment of watermelons.
A yield of 350 to 400 marketable melons per acre is good. A 32- to 34- pound melon, which loads 800 to 1,000 to a (rail) car, is considered standard, although melons weighing as little as 18 pounds and loading 1,600 to a car are shipped. On a basis of 350 melons averaging 34 pounds, the yield is practically 6 tons to the acre. This is above the general average, however, but yields of 4 to 5 tons to the acre are common.
Watermelons are what might be termed a catch crop in many sections and are profitable only where good yields are obtained or where the crop is grown on new land that is being cleared and put in condition for other crops. In other sections, however, watermelons are considered a standard farm crop and are grown in the regular rotation.
The handling of watermelons is extremely precarious on account of the many factors that govern their sale on the market. Overproduction is one of the chief causes of loss, but weather conditions at the market are perhaps the most important factor. Cool rainy weather will cause breaks of the market, while clear hot weather will invariably stimulate the demand.
TYPES OF SOIL ADAPTED FOR GROWING WATERMELONS
Rich sandy loam soils are considered best for watermelons, but good crops are often grown on almost any type of well-drained warm and fertile soil. Throughout the Southern States, where the bulk of the early commercial crop is produced, the melons are grown very largely on new ground that has been recently cleared of its timber, the soil of which is full of decayed vegetable matter and withstands dry weather better than land that has been cropped for several years. The newly cleared land also has the advantage that it ordinarily does not contain the diseases that so often cause serious losses of the crop.
This kind of soil, however, is very subject to infestation by the root knot nematode, and this fact should be taken into consideration in the selection of land on which to grow melons. Some of the heaviest yields are produced in the sandy river-bottom or delta soils of southeastern Missouri and in other sections having similar soil conditions. The essential requirements of soils on which watermelons are grown are that they be well-drained and warm, capable of being worked early in the spring, and contain an abundance of quickly available plant food.
As already stated, watermelons are frequently grown as a clean-up crop on newly cleared land. However, in many sections, such as southeastern Missouri and central Texas, very little land is now being cleared, and watermelons must be grown in rotation with other crops.
From the standpoint of disease control, watermelons should not appear in the rotation oftener than once in 6 and preferably 8 or 10 years. This applies particularly on land where root knot control is a factor. In such cases resistance of the rotation crops to root knot must be a primary consideration.
The intermediate crops in the South are usually corn and cowpeas, velvetbeans, cotton, winter oats, or peanuts, and in the North, corn and wheat, followed by clover or pasture. A crop of velvetbeans or clover turned under during the previous summer and allowed to decay will form an excellent supply of organic matter for the growth of watermelons. In Florida and southern Georgia the melons will be marketed in ample time for planting velvetbeans or cowpeas.
PREPARATION OF THE LAND
While watermelons are not an exacting crop as regards cultivation, it is essential that the land be well plowed and harrowed before being planted. On newly cleared land it is desirable that most of the sticks, roots, and trash that will interfere with cultivation be removed or burned, both before and after plowing. Quantities of small roots will be brought to the surface during the harrowing and fitting of the soil, and these should be piled around the stumps and later burned or hauled off the land. On old land, especially that which is in sod or has upon it a crop of velvetbeans, cowpeas, clover, or a similar crop, plowing should be done either in the fall or at some time during the winter when the ground is in suitable condition. Early in the spring the land should be thoroughly disked and harrowed or dragged before being planted. The same general preparation required for corn or cotton will apply to watermelons. While it is essential to have the land in good condition, too much expense is not justified. The work should be done by means of simple tools and economical methods.
MANURE AND FERTILIZERS
Barn or feed-lot manure free from the fungus causing wilt of watermelons may be used as a fertilizer at the rate of 4 to 6 tons to the acre, but it should be reasonably well-rotted and thoroughly mixed with the soil. The wilt fungus grows readily in stable manure, and a common source of infection is the feeding of hay containing diseased watermelon vines cut from fields after the crop is off. In districts where wilt is prevalent growers are advised to use extreme care to prevent the manure supply becoming infested; also to depend mainly upon soil-building crops and commercial fertilizers as sources of plant food.
The method of distributing manure will depend on the quantity available and the system of planting the watermelons. If not more than 3 or 4 tons to the acre are available and the melons are to be planted in hills, the manure should be worked into the hills. Where the melons are grown in a continuous row the manure is scattered in a furrow and a double furrow thrown over it, forming a slight bed, on which they are planted. If more than 3 or 4 tons of manure to the acre is available it can best be broadcast or scattered in a strip along the row and thoroughly disked into the soil. Experience has shown that manure, even where the quantity is small, worked into the hills or rows is of decided value in giving the plants a strong early growth; provided, however, that the manure is free from the wilt fungus.
In the Texas watermelon districts the soils usually contain an abundance of potash, and in many cases a fertilizer consisting of equal parts of cottonseed meal and 16-percent superphosphate is applied at a rate varying from 200 to 600 pounds to the acre. Many Texas growers use ready-mixed fertilizers; some, however, use superphosphate alone, especially on new land.
The watermelon growers of Missouri, southern Illinois, and other melon-shipping sections have developed local practices regarding the application of fertilizers, but as a rule not less than 200 pounds nor more than 800 pounds of a well-balanced mixture is applied. Many growers follow the practice of placing a little extra fertilizer directly in the hills and mixing this thoroughly with the soil, the object being to give the plants a good send-off.
GOOD SEED, ITS IMPORTANCE
A pound of good watermelon seed is sufficient for planting an acre, with a small amount left over for replanting. Poor seed has been responsible for many of the failures and low yields of watermelons.
Any watermelon grower can grow their own seed with very little trouble, as a small number of choice melons will furnish enough seed for planting his crop; in fact, four or five average melons will yield a pound of seed. The proper method of selecting the seed melons is to go through the field prior to the first picking and mark a number of melons having the desired type, color, and general characteristics. In making the selection, vigor and freedom of the vine from disease should be taken into consideration. The individual melons selected for seed saving should be free from anthracnose markings and decay. One of the best methods of marking them is to tie pieces of white cloth to the stems of the melons. The marked melons should be allowed to remain on the vines until fully ripe, then carried to a safe place, and after 2 or 3 days of additional ripening should be opened and the seed separated from the pulp. An acre of watermelons grown exclusively to seed purposes will yield about 200 to 250 pounds of seed.
The usual method of saving seed is to split the melons lengthwise, scrape out the seed-bearing pulp and allow it to ferment in wooden tubs or barrels for 24 to 36 hours, or until the pulp begins to sour and float to the top, the seed settling to the bottom. Water is then added, the pulp poured off and the seeds washed through several changes of clean, cold water. The seeds should then be spread thinly on cotton sheets and dried, being stirred occasionally during the drying process.
Where any considerable quantity is handled, trays or frames of laths about 3 by 6 feet in size, covered with thin burlap or cheesecloth, are desirable for drying the seed. After the seeds are thoroughly dried on the sheets or trays they should be stored in rather small quantities in thin cotton or burlap bags and kept where they will be safe from mice in a cool, dry, well-ventilated place. Some seed growers maintain that it is best to cut off the ends of the melons, saving the seed from the center portion only. There is nothing to indicate that this has any particular advantage, however, the essentials being that the seeds are fully ripe and that they are given the proper care after their removal from the melons.
Where a grower has an especially fine lot of melons that are uniform and true to variety but for which there is no market, it will often pay him to secure some barrels and other equipment and save the seed, as described above. Seed saved in this manner may be sold to the melon growers in the immediate neighborhood the following season, thus turning what might have been a complete loss into a reasonable profit.
PLANTING DATES AND METHODS OF PLANTING
Because the young plants are easily injured by frost the seed should not be planted until the soil is warm and danger of frost is past. To avoid the possibility of loss from frost, growers frequently follow the practice of putting in an additional planting of seed 3 or 4 inches in one general direction from where the original planting was made, this being done from 3 to 5 days after the first planting. In case of actual injury a third seeding is sometimes made to insure a stand of plants. The thinning of the plants should begin as soon as they are up, leaving first about three plants in a hill and later reducing the number to two or in most cases one. Where a second or third seeding is made and the first comes through in good condition, those of the first seeding should be left, provided they are in good healthy condition.
Planting distances vary to some extent, but not greatly, in the different commercial watermelon-producing localities. A few of the southeastern growers plant as closely as 8 by 10 feet and others 10 by 12 feet, but 10 by 10 feet is perhaps the more popular planting distance. By having the rows 12 feet apart, cultivation can be continued longer in one direction. The hills should always be checked in both directions in order that the crop may be cultivated both ways during the early part of the season. Texas growers, who secure the greatest return per acre, plant at distances averaging 12 by 12 feet. Many of them give the hills practically the same space by planting 10 by 14 feet. This arrangement gives approximately 300 hills per acre. Where melons are planted in continuous rows in one direction only, the rows are spaced 14 to 20 feet apart and the plants thinned to a single plant every 6 or 8 feet. When planted in hills, the plants are thinned to one or at most two plants in a hill. The best yields of high-grade melons are produced where the hills are spaced at least 10 by 12 feet and the melons thinned to one plant in a hill. This distance gives about 360 hills to the acre, and with 2 melons to the hill the yield should be about 700 melons to the acre, or 450 to 500 marketable melons.
The methods of planting watermelons are similar in all localities, the custom being to harrow the ground and then mark off in both directions. Where manure is worked into the hills the seeds are usually scattered slightly and pushed into the soil with the finger ½ to 1 inch deep. Where no manure is used, the seed is often planted directly in the cross marks and covered by hand or with a hoe. Three seeds are sufficient, but six or seven are usually planted in each hill, to insure a good stand. Where the melons are planted in a continuous row or drill, the seed is often put in by means of either a hand drill or a one-horse drill. A seed drill, however, usually involves the use of larger quantities of seed than are required for hand planting.
The cultivation of watermelons should begin within a few days after the plants come through the ground. Where the hills are carefully checked in both directions the land can be worked for some time with a harrow or weeder with a little hand work directly around the hills. Some growers follow the practice of running along the rows with a one-horse cultivator or a two-horse riding cultivator and then working out the middle with a harrow. As a rule, about three or four general cultivations will be sufficient, but frequent cultivations early in the season not only keep the ground in good condition but prevent the growth of weeds. Later, when the vines begin to spread, it may not be possible to cultivate both ways but in one direction only. By training the vines more or less in a well-defined row, cultivation can be continued in one direction until the melons are two-thirds grown. It should be borne in mind that the watermelon is a comparatively shallow-rooted plant and that the roots often extend farther than the vines. Therefore, it is essential that the land be worked shallow, especially near the hills and after the vines begin to run freely.
Growers of high-grade watermelons have found it desirable to thin or “prune” the melons in order to get fruits of shipping size. This does not mean pruning the vines themselves, but reducing the number of melons on each vine. It has been found that any cutting back or disturbance of the vine injures the development of the melons. The usual custom among growers is to wait until there is a good set of melons on the vines, the largest being about 4 inches in length, and then to remove all but two of the best melons from each hill or vine. Sometimes as many as three or four melons are left at first, the two best ones remaining after a second pruning, which occurs about a week after the first. It is doubtful, however, whether two prunings pay, for as a rule the work can all be done at one time. Pruning should be done only when the vines are dry, so as to avoid the spread of anthracnose.
In order to avoid stooping to cut off the undesired melons, some growers use a long-handled knife or cutter with which the melons can be snipped off. Others use an ordinary penknife, as they consider it necessary for the person doing the pruning to examine the melons more carefully than can be done without stooping over. A cutter can easily be made by sawing a slit in one end of a broomstick, inserting a thin piece of steel, and fastening it with rivets or screws. The outer edge of the steel blade is kept sharpened. In using the cutter the blade is simply placed upon the stem that attaches the melon to the vine, and with a slight downward thrust the stem is severed close to the melon, care being taken that the vine is not cut or injured.
Pruning causes the entire vigor of the vine to go to the development of the melons that are left and usually results in the production of a high percentage of marketable melons. Later in the season after the marketable melons are practically mature, the vines often put on a second crop, which is either sold locally or used for hog feed. Some of the smaller varieties are not pruned so closely, four to six melons being left on the vine. Melons grown for home use are seldom pruned, as the question of size is not so important.
INSECT ENEMIES OF THE WATERMELON
The watermelon plant is subject to attack by numerous insects. Of these, the melon aphid (Aphis gossypii Glov.), the striped cucumber beetle (Diabrotica vittata Fab.), and cutworms are considered enemies of primary importance.
MELON APHID. The melon aphid, or melon louse, does much harm to the growing plant in reducing its vitality and deforming the leaves. Its presence is first manifested by a slight curling of the leaves, and later by an excretion of the insect known as honeydew and also by the appearance of large numbers of ants or lady beetles. When the melon aphid becomes very abundant the leaves curl up and the growth of the plant is greatly retarded, and oftentimes the plant dies. Since leaf curling is also a symptom of certain diseases, the under sides of the leaves of the affected plants should be examined for aphids.
STRIPED CUCUMBER BEETLE. The striped cucumber beetle is especially injurious to young plants just after they come through the ground.
CUTWORMS. Cutworms sometimes cut off the stems of young watermelon plants at the surface of the ground.
DISEASES OF THE WATERMELON
Watermelons are subject to several very destructive diseases, the most important of which are wilt, root knot, anthracnose, and stem-end rot.
WILT. Fusarium wilt is in some sections one of the most destructive of the field diseases. The experience of many years has established the fact that two successive crops of watermelons cannot be grown on the same land without risk of failure and that 10 or more years must elapse before old melon fields may be replanted with reasonable safety. The control of this disease lies in planting on new ground or in a rotation of sufficient length to safeguard against loss. In laying out rotations, care should be taken to locate melons so that the field will not be washed by drainage water from higher land that was planted to melons the previous year. As the causal organism may live over in manure, it is important to avoid the use of manure from barnyards where stock had fed on hay or refuse from melon fields.
ROOT KNOT. In certain sections of the melon territory, particularly where the land has been under cultivation for a number of years, the control of root knot is a serious problem. Planting on new land or long-time rotations with immune crops are the surest safeguards against root knot.
ANTHRACNOSE. Anthracnose affects both leaves and fruit and is probably the most important of the watermelon troubles. The causal organism has been so widely distributed on the various vine crops that the disease is almost certain to occur in any growing section if there is a prolonged rainfall or a period of high atmospheric humidity. Its presence is first made known in the field by the characteristic irregular, dark, dead spots which appear on the leaves, eventually causing them to curl up and die. From the foliage and stems the disease spreads to the fruit, where it causes water-soaked spots or pimplelike lesions, which under moist conditions become sunken and covered with a layer of pink spores.
If the trouble becomes general in a field before the melons have ripened, the crop is usually a complete failure. It often happens, however, that the disease appears as the melons are approaching maturity. Under these circumstances, although the pockmarked fruit may be harvested and shipped, it often rots in transit and at best brings but a poor price at the market.
STEM-END ROT. Stem-end rot is caused by a fungus closely related to or identical with the organism which causes Java black rot of sweet potatoes, one of the stem-end rots of citrus fruits, a cotton-boll rot, and diseases of some other plants commonly grown in warm climates. It is particularly destructive in the case of melons shipped from the Southeastern States. In the spring this fungus is found in and around melon fields fruiting on dead stalks of coffee weed, corn, cotton, and other plants. Spores or fungus seed bodies are washed into the soil or carried about the fields on implements or by the wind. Provided these find lodgment in a wound or on the cut stem of a watermelon, decay soon results. As the season develops, melons may be found rotting in the field as a result of infection at imperfect blossom ends or at cuts or anthracnose pockmarks. These rotting melons are the chief source of infectious material which serves to bring about stem-end rot in transit.
As has been stated, infection and subsequent decay occur when these spores get into wounds affecting the stem or rind of a melon. Bruises and cuts of the rind can be prevented by careful handling, and this is most important. A cut stem, however, is a wound that is present on all melons, and it is to prevent infection at this point that the practice known as stem treatment has been recommended.
The control of the stem-end rot in transit involves field sanitation supplemented by reclipping and treating the stems of the melons with a disinfectant paste when packing the car, or when loading them on trucks or wagons to be hauled to nearby markets. As a first precaution, in order to avoid contamination with hands and implements, the men who are harvesting the melons in the field should never touch or cut into a decayed melon. The fruit should be clipped with the longest possible stems and hauled to the car without delay, as the harvested melons left in the field or on wagons from one day to another may become infected and rot in spite of a late treatment. Handle carefully to avoid injury to the rind, and load only sound melons with fresh green stems. As each tier of melons is placed in a car, cut a short piece from the stem by means of a sharp knife and immediately treat the freshly cut surface with the disinfectant paste.
GATHERING AND LOADING WATERMELONS
There are several well-known tests for the maturity of watermelons, but the most practical one in use is that of the change in color, especially that of the lower part of the melon where it rests upon the ground. This consists of a slight yellowing of the white background color, which previous to maturity is a pale white. In the final analysis the sugar content of the flesh and the ripeness of the seeds is the real test, but this cannot be applied in a practical way; therefore, exterior indications are the only ones by which to judge the maturity of the individual melons.
Melons should be cut from the vine rather than pulled or broken off. Ordinary penknives with rather slender blades about 2 ¼ inches in length, or stiff-backed knives, such as are employed for peeling fruit, are adapted for cutting melons from the vines. Care should be taken to leave the stems as long as possible. Melons should not be stood on end either in the field or on the wagons.
Care must be taken in laying the melons down (1) to avoid injury to the skin from the numerous small sticks that are so prevalent in new ground and (2) to pile the melons one upon another carefully, to prevent bruising. The melons should not be piled more than three high and in no case should they be stood on either end.
It is desirable in all cases that a bed of about 5 inches of straw or soft pine needles be placed in the bottom of the wagon or truck and that the sides and edges of the body be padded with burlap or canvas. Before the movement of the melon crop begins, the body should be inspected carefully to see that no nails or cleats with sharp corners are left to injure the melons. Where ordinary farm wagons are employed it is very desirable that they be provided with an extra thick bed of straw and bolster springs, to lessen the jolting of the melons.
In no case should the melons be loaded more than five deep, nor should the laborers be allowed to either walk or ride upon the load. The most careful growers cover the load of melons with a piece of canvas to protect them from the hot sun on the way to the cars. All melons cut from the vines during the day should be placed in the car and not allowed to remain in the field, on the wagon, or piled in the center of the car overnight.
In clipping the stems for stem-end treatment a very sharp knife or razor should be used and a clean smooth cut made. Shears or clippers are not adapted for this work, as they have a tendency to bruise or crush the stems.