WATERMELON Citrullus lanatus

(photo provided by www.acesag.auburn.edu)

FAMILY CHARACTERISTICS
    The Cucurbitaceae family is composed of many species of "vine crops" with spreading growth habits that are all warm season annuals.  The crops of the family prefer hot and humid weather as is found in the southern United States to dryer climates.  Typical of all cucurbits are tendrils that are found at the leaf axis of the stem.  This is the structure that allows the vine to wrap around structures for support.  The essence of the cucurbits, however, is how the fruit is formed.  The ovary (fruit) is fused with the receptacle tissue (essentially the outer covering of the ovary) to form a hard rind.
    The Cucurbitacea family contains many species and varieties of zucchini, squash, and pumpkins, cucumbers, and many other melons such as muskmelon, cantaloupe, and honeydew besides the hundreds of watermelon varieties available.  So many varieties are available because of the ability of the cucurbits to cross-pollinate within the same species.
    These vegetables have a large variety of uses from fresh salads and deserts to pies, vegetable entrees, snack food, and ornamental decorations.
    Other family members include:
        Benincasa hispida L.; Uax Gourd
        Citrullus lunatus (Thung.) Mansf .; Watermelon
        Citrullus lunatus var. citroides (Bailey) Mansf.; Citron, Preserving Melon
        Cucumis anguria L.; West Indian Gherkin
        Cucumis melo L. (Chito group); Mango Melon, Garden Lemon
        Cucumis melo L. (Conomon group); Melon, Oriental Pickling Melon
        Cucumis melo L. (Flexuosus group); Armonian Cucumber, Japanese Cucumber, Uri
        Cucumis melo L. (Inodorus group); Melon, Muskmelon, Winter Melon
        Cucumis melo L. (Reticulatus group); Melon, Muskmelon, Cantaloupe
        Cucurbita maxima Dutch.; Winter Squash, Pumpkin
        Cucurbita mixta Pang.; Pumpkin
        Cucurbita moschata Poir.; Winter Squash, Pumpkin
        Cucurbita pepo L.; Winter Squash, Marrow, Summer Squash, Pumpkin
        Cucumis sativus L.; Cucumber
        Lagenaria siceraria (Mol.) Standl.; Bottle Gourd
        Luffa acutangula Roxb.; Angled Loofah
        Luffa cylindrica Roem.; Smooth Loofah
        Momordica charantia L.; Bitter Gourd, Balsam Pear
        Sechium edile S.W.; Chayote
        Telfairia spp.; Oyster Nut
        Trichosanthes anquina L.; Snake Gourd

CROP HISTORY AND DEVELOPMENT
    Although native to central Africa, the watermelon was first grown by ancient Egyptians and is believed to also have been cultured in Asia minor, Russia, and the Near and Middle East thousands of years ago.  The uses for the watermelon at this time included a source for water (watermelons are comprised of 90% water), staple food, animal feed, and fermentation for alcohol production.  Wild and early watermelons were extremely bitter, but this was eliminated quickly under cultivation with the selection of seed and cross-pollination.
    The watermelon arrived in the Americas in the early 1600's and was first cultivated in Massachusetts in 1629.  By the middle of the 17th century, the watermelon had made its way down to Florida.
Today, there is over 184,000 acres of commercial production found mainly in Florida, Texas, and California, with over 1,182,800 metric tons being produced in the United States per year, roughly equivalent to 100 million melons per year.  Americans consume approximately 13.2 pounds per capita per year.
    In Georgia, approximately 30,000 pounds can be grown on one acre if irrigated. Roughly 40,000 acres are put into watermelon production each year in Georgia, mainly as an agronomic substitute or part of field rotations.

PLANT CHARACTERISTICS

Overview Citrullus lanatus is an aggressive vining annual that prefers temperatures greater than 70°F.  It is grown for its large fruit that weigh from five to forty pounds, depending on variety.  The root system of the plant is a deep, spreading fibrous semi-taproot system that extends six feet or more below the soil surface.  The leaves are deeply lobed, pubescent, and dark grayish green.  The plant is monoecious, meaning that it produces both male (staminate) and female (pistillate) flowers.      The fruit are born from epigenous ovaries (below the flower sepals) from the pistillate flowers.  The ovary resembles a small watermelon, and the female flower is easily distinguished from the male flower in this way.  Flower pollination is accomplished through honeybees, and ten or more visits to each flower are required for proper pollination.  Seeds are produced inside the fleshy fruit and can range in color from black to white with 250-500 seeds per ounce.      Sugar content and sweetness are the critical factors in determining the quality of the many cultivars of melons.  The accumulation of sugars takes place in the later stages of fruit development and can be slowed by excessive rains or severe drought, nutrient stress, or by disease and insect damage to the foliage of the plants.

Watermelon Flowers

Cultivars/Varieties  There are hundreds of cultivars available for production and contain much diversity, with varieties having dark green to yellow rind colorings that can be either striped or solid and either contain seed or are seedless.  The seed usually are white or black, with immature seed in black seeded melons being white.  The shape of the watermelon varies from round to elliptical depending on the variety.      Selection of a cultivar for production should be based on the optimal yield and profit that can be obtained.  Also, the market availability of seed or transplants and ripe melons, the equipment resources available to the grower, and cultural conditions of the site should be taken into consideration.      The most commonly planted varieties of watermelon in the state of Georgia are 'Crimson Sweet', 'Jubilee', and 'Charleston Gray'.  These have been chosen for a variety of factors, including amount of accumulated sugars, drought tolerance, and insect and disease resistance.      Seedless watermelons are a sterile product of the cross between a tetraploid male plant and a diploid female plant resulting in triploid offspring.  Essentially, the chromosome set is incomplete and therefore the offspring, while they still produce fruit, are sterile.      Hybrid crosses are beginning to take rise to the watermelon industry.  Hybrids between varieties or cultivars allow growers to produce plants and fruit that exhibit both the qualities found in one variety and the qualities of another.  For example, if one type of watermelon had a high resistance to the cucumber beetle and average sweetness while another variety had excellent sweetness and low resistance to the cucumber beetle, these two could be cross pollinated to get the beneficial qualities of both melon varieties.     Hybrid seed cost ten to fifteen times more than regular seed, but most growers find the cost is justified by the benefits.  These benefits include a higher yield potential, higher disease and insect resistance, higher uniformity rates, and overall higher quality.     Icebox watermelons have become increasingly popular with today's consumer.  Icebox varieties are only 5-10 pounds while an average watermelon can weigh up to 40 pounds.  This is more efficient and easier to handle for the typical consumer, who only consumes 13 pounds in one year.

L to R: 'Royal Majesty', 'Royal Sweet', 'Paradise', and 'Oasis' Varieties  (photo provided by  www.acesag.auburn.edu) Red flesh cultivar Yellow flesh cultivar

PROPAGATION METHODS
    The propagation of watermelons can either be accomplished by seed or by transplants.  Planting is usually done either by hand on raised beds called hills, or mechanically with a seed drill.  Planting needs to occur when the soil is moist.

Seed Watermelon seed germinate at temperatures between 68° and 95° F.  At 77° F, seed germinate and emerge within five days.  Planting of the seed should be delayed until the danger of frost has past.  If planted early, many growers will supplement the first planting with a second planting 7-10 days later to account for any seed that might have been lost due to frost.  However, this becomes expensive quickly when using hybrid seed, and is not worth the return gained by having early watermelons.      Seed should be planted at a depth of 1” and planting usually requires 1-2 pounds of seed

'Crimson Sweet' seed

for establishing one acre.  With intensive management, 1500 plants can be placed on one  acre.  Without intensive management, only 900 to 1000 plants per acre should be planted.  Certified seed should be used and will have 85-90% germination and be labeled, uniform, and disease free.     Plant spacing varies widely. It is common to over plant a hill and thin it to the desired stand once plants begin to establish.  This practice is also very inefficient when using hybrid seeds and has caused many growers to start using transplants.

Plant emergence

    Transplants  Transplants are gaining in popularity.  When producing an early crop to have the first melons to market, a grower can use transplants and get a 2-3 week jump start over the growers who propagate by seed.
    There are several concerns with using transplants.  When using transplants it is critical to ensure that the plant material is less than seven weeks in age.  If the transplants are older, the plants will never perform well.  Signs of older plants include nitrogen or iron deficiencies (yellowing of the leaves), and flowering. Elongation of the stems will occur during bad weather as the plant “stretches” to receive the maximum amount of light it can.  This elongation can cause transplants to be very difficult to transplant and care should be taken to avoid bad weather when seedlings need to be held over from purchasing to planting.
Many horticultural growers are finding that it is beneficial to grow the transplants that they will need.  This lowers the cost of the operation plus it lowers the risk of importing foreign (to the grower's fields) pathogens such as insects and diseases.
    Success depends on four requirements: a commercially prepared media free of weed seed, insects, and diseases; adequate amounts of heat and water; adequate amounts of high quality light; and a 3-4 day hardening off period.
    One important factor is that watermelons suffer transplant shock and should not be disturbed.  Therefore, the containers that the transplants are grown in should be the containers that will be transferred to the field and should be large enough that the plant doesn't become root bound during that time.  A 3” by 3” container can be used efficiently to minimize root ball disturbance.  Peat pots are an exceptional option that allows the plant to be set out in the pot with absolutely no root disturbance.
    Pollination  Watermelons produce separate male and female flowers on the same vine. A female flower can be easily recognized by the swelling of its base which resembles a tiny watermelon. Normally a female flower may be found at every seventh to tenth node. Thus plants usually produce about 10 times more male flowers than female flowers.

Pollination is the transfer of pollen from the male flower to the female flower. Pollen must be transferred from flower to flower by pollinating insects - primarily honey bees. For proper pollination, a female flower should receive eight or more bee visits. If adequate amounts of pollen are not deposited in every female flower, the melon either will not  "set" or will be misshapen and probably culled at harvest. Either of these situations results in reduced yields and quality. Female flowers that do not set normally lose their green color, shrivel, often turn black and finally abort (separate from the vine). This occurs with little or no increase in size.     Keep in mind, however, the abortion of flowers and small immature melons does not always indicate insufficient pollination. A watermelon plant is able to sustain only a limited number of melons. Subsequent melons, regardless of how well they may have been pollinated, routinely abort while small.

Female (left) and male  (right) flowers

The exact number of melons a plant will set and size depends on cultivar (those typically producing smaller mature melons will set more of them), soil fertility, availability of moisture and other growing conditions. However, a good watermelon field (planted to a 25 to 30 pound cultivar) will set and appropriately size two or three melons per plant on the average.     Honey bees work watermelons primarily in the morning beginning one to two hours after sunrise when the flowers first open. Visitation continues until about mid afternoon, depending on the temperature and other weather conditions. Midmorning is usually the peak period of bee activity, however, cloudy, rainy, or unseasonably cool weather usually restricts bee activity. Individual watermelon flowers open for only one day and must be effectively pollinated that day if good yields are to be obtained. Since numerous visits are required to each flower during a relatively short period of time, it is necessary that sufficient numbers of bees be available near the field.

Immature watermelon.  Poor shape due to  insufficient pollination.

   Watermelon flowers are not nutritionally attractive to honey bees. Therefore, blooming weeds or other crops can "out compete" watermelons in attracting honey bees. Where possible destroy any significant populations of weeds which might also bloom concurrently with the watermelons.
    To help insure an adequate number of bee visits per flower, both the number and distribution of honey bee colonies must be considered. A good, strong colony consists of approximately 30,000 bees housed in a two-story hive. Although the number of colonies required may vary from field to field, it is usually advantageous to supplement native wild bees with at least one strong colony for every three to five acres of melons. The movement of beehives into the field should coincide with first bloom.
    The most efficient pollination occurs when hives are placed throughout the field, however, actual colony distribution is usually dependent on field size. Honey bees pollinate most efficiently within 100 yards of their colony and flights of any greater distances reduce pollination. Colonies may be placed along the borders of fields smaller than 40 acres. In larger fields the colonies should be placed within the field in clusters of hives at distances not exceeding 500 to 600 feet in all directions. This will encourage the bees to distribute themselves more uniformly over the flowers.
    When weather conditions are favorable for bee activity, fields should be checked daily, preferably during midmorning, until adequate melon set is achieved. If numerous bees are not vigorously working watermelon flowers, corrective action must be taken immediately to prevent poor or delayed set.
    Bees require water for survival and their efficiency may be improved by a water source near the hives. Some shade may also be beneficial. Exercise extreme caution to minimize the exposure of bees to insecticides. For their protection, it is best to apply insecticides in late afternoon after bee activity diminishes.
    “Plug Mix Planting”  This is a process that is gaining popularity because of the ease and success rate of the method.  Seed is mixed with water and fertilizer plus a media consisting of 2/3 peat and 1/3 vermiculite and is allowed to sit for 24-48 hours to let the seed absorb and begin the germination process.  This mixture is planted with injectors, placing 1/8 to 1/2 cup of the mixture per hill.
    Thinning Practices  Usually seeds are over planted and then thinned when plants start to emerge.  A 2 step process is used to reduce the stand of plants.  The primary thinning occurs at emergence and should reduce the number of plants gradually to the desired stand number with four or five plants being left per hill.  The secondary thinning should be done when plants are well established and several true leaves have developed.  At this time, the plants should be thinned to 1 plant per hill (two if selection is not good).

CULTURAL PRACTICES
    Overview  Watermelons need an average of 4 months to mature, from 80 to 120 days.  A loose, friable sandy loam soil is preferred: compacted layers can be very detrimental to root development.
    Soil  Watermelons thrive in fertile sandy loam soils containing organic matter with a pH of 6.0-6.5.   Soils should be turned over 7-8” in the fall to allow for complete degradation of plant material and planting beds should be formed by one of three ways: Disking and subsoil bedding, disking and moldboard plowing and bedding, or disking, moldboard plowing, and subsoil bedding.  For early production, plants should be planted on a raised bed.  Disking after plowing should be avoided, because studies show that this process only leads to more compacting in the soil.
    Another option of planting is hills.  Hill formation should be formed on a 10 by 10 foot to a 12 by 8 foot row spacing and are formed by intersecting furrows.
    Temperature  The watermelon is a warm season annual.  Therefore it prefers temperatures above 70° F for optimal growth.

Fertility  Since watermelons are grown in sandy loam soils, leaching of minerals and nutrients can be quite a problem.  Regular soil tests and tissue analysis should be conducted throughout the season.  When soil test levels are low, apply 120 pounds per acre of nitrogen, potassium, and phosphorus.  It is recommended to apply a pop-up fertilizer 2-3” below the seed line before seeding or transplanting of approximately 100 to 150 pounds of 10-34-0.  Current recommendations include applying phosphorus and micronutrients plus one third to one half of the N and K requirement from the soils test at planting and following this with two more applications at 3 and 6 weeks of the remaining N and K.  Of course these are only recommendations and results will vary widely between different soil types and areas.  To be absolutely sure of nutrient levels, have soil tests and tissue tests performed regularly.  It is recommended to perform tissue analysis on 8 to 12 day intervals.

Copper deficiency in watermelon (photo provided by APS Press)

    Weed Control  Common weeds in the Southeast include Sicklepod, Yellow and Purple Nutsedge, Florida Beggarweed, and Cocklebur.  Fields with perennial weeds such as bermudagrass should be avoided due to continued problems season after season.
    The best method of weed control is a mixture of pre-plant mechanical weed control and post-plant chemical weed control.  If cultivating for weeds after plant establishment, care must be taken not to disrupt the root system of the crop.  Cultivate only the top 2” of soil in the furrows.  If hills are used, do not mechanically cultivate.  If damage to the root system or to the stem occurs, rolling will begin to occur, essentially destroying vine integrity and thereby ruining fruit crop for that vine section.
    In the fall, turn the soil over to a depth of 7 to 8” to bury and allow all vegetation enough time to decay. Contact your local extension office to find out what chemicals are currently approved for the control of these weed species.
    Irrigation  The watermelon is comprised of 90% water, approximately 4 gallons for a forty pound melon; therefore, water supply is critical during the growth and development of the plant and fruit.  Water shortages will cause noticeable gaps in production with a reduction in leaf area and overall yield.  Supplying water throughout the growth of the plant is important, but absolutely critical during flowering and development of the fruit.
    Most watermelon fields in the south are irrigated through an overhead system.  This can be a center pivot design, a linear move system (very efficient for rectangular shaped fields), a traveling big gun, or a permanent set of portable aluminum pipe and risers.  Fertigation can be used with good results through this last method.
    In Georgia, drip irrigation is becoming a popular method for irrigating watermelon crops.  This method is very efficient for melon crops grown on plastic.  Through drip irrigation, 40% less water can be used, fewer weeds are prevalent, and earlier yields are obtained.  These benefits help dramatically reduce the cost of installing drip irrigation.
    Watermelons transpire 0.3 inches per day.  To account for this, irrigation should occur two to three times a week (in good weather) with 0.5 - 0.8 inches of water being applied at each application.  The primary focus of irrigation is to keep the top few inches of soil moist at all times, but to keep the soil from being waterlogged.
    For more precise irrigation scheduling, a tensiometer or similar field device should be used to determine available soil moisture.  From this data, scheduling can be used to water only when needed, thereby saving even more in irrigation costs.  Remember to apply 10-20% more than transpiration needs to account for wind drift and evaporation.  Drip irrigation will need to be operated more frequently than overhead due to the nature of the water flow confined to the root zone.
    Turning  Watermelon vines need to be ‘turned’ or adjusted to keep the runners in the proper direction.  This allows for clean furrows for movement and cultivation between plants without damaging the vines.  This turning should occur before runners are established with adventitious roots and should only occur once per runner to prevent damage and rolling of the
vine.
    Pruning Watermelon plants need to be pruned of excess fruit to allow the correct number of fruit to properly develop and obtain marketable size.  Pruning should occur in two stages.  The first pruning removes all of the culled (unmarketable) fruit while the second removes the late set fruit in order to increase the size of the remaining melons.  There should only be 2 melons per vine (5 per vine for icebox varieties) after pruning.

INSECTS
    Insects that affect many of the other cucurbits such as squash and cucumber also affect watermelon.  Aphids, cucumber beetles, leaf miners, leaf hoppers, red spider mites, wireworms, cutworms, and pickle worms are insects that might cause a grower problems with his or her crop.
    Proper scouting frequently is the best method of controlling insect populations.  Proper control techniques vary for all insects, with some insecticides actually creating more favorable conditions for other insects.  Contact your county extension agent for more information pertaining to scouting, population sizes, life cycles, and the proper management of the invading insect.
    Honeybees. Since honeybees are the vectors for pollination in watermelons, extreme care should be taken when spraying pesticides that populations of honeybees are not killed.  Honeybees are most active in the mid-morning, but activity can continue into the afternoon until dusk.  Insecticides should be applied in the late afternoon after bee activity has diminished in order to prevent bee kills.  If large acreage has to be sprayed, hives should be removed the day before the application.

DISEASES
Diseases prevalent in watermelon crops are:

Anthracnose, caused by the fungus, Colletotrichum lagenarium, can be a very destructive disease of watermelons. This fungus attacks all above-ground parts of the watermelon plant. Plants can be infected at any stage of growth, however, disease symptoms are first noticed as round to angular reddish brown spots on the oldest leaves. Spots may later dry, turn almost black and tear out, giving a leaf a ragged appearance. Often the leaves at the center of the plant are killed first, leaving the stem and a portion of the runners bare. After a few days of warm, rainy weather, every leaf in an entire field may be killed, giving the field a "burned over" appearance.     Light brown-to-black elongated streaks develop on the stems and petioles. Round, sunken spots may appear on the fruit. Spots first appear water soaked, then turn a dark green to brown color. The pinkish colored ooze often noticed in the center of the sunken spot is spores of the fungus.     There are three types of the Anthracnose fungus, known as Races 1, 2, and 3. Our most common watermelon varieties: 'Charleston Gray', 'Blackstone', and 'Congo' are resistant to Races I and 3, but not to Race 2. In recent years, Race 2 has become widespread in Georgia. It has severely damaged watermelon varieties which have previously shown anthracnose resistance. In areas where all three Races of the fungus are present, no variety is resistant to anthracnose.

Anthracnose on watermelon leaf Anthracnose on fruit

Downy Mildew  Downy mildew is caused by the fungus, Pseudoperonospora cubensis. This fungus attacks only the leaves of watermelons. Lesions first appear on the oldest crown leaves as yellow, mottled spots with indefinite borders blending gradually into healthy portions of the leaf. Older lesions are dark brown with a slight yellow border. As the disease progresses, brown areas coalesce causing leaf curl inward toward the midrib. Under favorable conditions for disease development, downy mildew develops rapidly, resulting in a scorched appearance over an entire field. The pathogen is air-borne and usually begins in areas south of Georgia and move up the coast destroying watermelons in its path. Downy mildew has not been a problem in watermelons in the last few years, however, the potential is there and plantings should be observed frequently for signs of downy mildew.

Downy mildew on leaf

Fusarium wilt  Fusarium wilt of watermelons is caused by the fungus, Fusarium oxysporum f. niveum. Fusarium wilt is widespread in many fields in Georgia. Symptoms of fusarium wilt can occur at any stage of growth. Infected plants develop wilt symptoms on one or more runners usually beginning at their tips. The vascular tissue in the lower stem and roots develop a light brown discoloration. In severe cases, the entire root may become dark brown and a soft rot develop near the crown. The pathogen can spread to new areas on seed or in soil transported by equipment, drainage water, and man. Several varieties are considered somewhat  resistant to this disease. However, even with resistant varieties it is desirable to use new land or have a minimum of eight years between diseased crops on the same land. On old land, some wilting can occur even with resistant varieties and final thinning should be delayed as long as possible to eliminate the great number of wilt-suspectible plants before final stand is established. Contamination of new fields with soil from Fusarium infested fields should be avoided.

Fusarium wilt

Gummy stem blight  Gummy stem blight is caused by the fungus, Mycosphaerella melonis. This has been the most serious disease affecting watermelons in Georgia, the past few years. This fungus can cause damping off, crown rot, leaf spot, stem canker, and fruit rot of watermelons. Lesions on the cotyledons and leaves are round or irregular and brown in color. Lesions on the crown and stem are brown and usually turn white with age. Early infection usually comes from diseased seeds. On older leaves, brown-to-black spots develop between the leaf veins. The first spots usually occur in the lobes of the leaves.     Gummy stem blight spreads from the center of the plant outward. As the season advances, gummy stem blight attacks vines causing elongated, water soaked areas that become light brown to gray. Vine cankers are most common near the crown of the plant. Gum oozes from the stem cracks, and runners usually die one at a time. It is unusual to find gummy stem causing fruit rot in watermelons.

Gummy stem blight

Watermelon mosaic virus  Watermelon mosaic virus is caused by two different viruses; these are referred to as Watermelon Mosaic Number I and Watermelon Mosaic Number I. The most common symptom is mottling of the leaf, however, mottling may be difficult to see under certain weather conditions. Some plants are stunted with abnormal leaf shapes, shorten inner nodes, and bushy erect growth habits of some runner tips. The first symptoms on the fruits are usually bumpy and mottled appearance of the fruit surface. This disease symptom is more expressed in periods of extended high temperatures which occur just before watermelon harvest here in Georgia. The diseases usually spread by aphids which can spread through an entire planting during the growing season.

Watermelon mosaic virus

Rind necrosis  Rind necrosis is reported to be caused by a bacterium, Erwinia spp. The symptom of this disease is the development of light brown, dry, corky spots in the rind, which may enlarge and merge to form rather extensive necrotic areas that rarely extend into the flesh. Although there are no external symptoms of rind necrosis, infected fruits appear to have exceptionally tough rind. It is not known how this disease is transmitted, but it apparently is limited to fruit infection.     Watermelon varieties differ in the relative incidence and severity of rind necrosis. The varieties 'Sweet Princess' and 'Jubilee' are least affected, 'Charleston Gray' and 'Charleston Sweet' are moderately affected, while 'Crimson Sweet' is most affected by this problem.

Rind necrosis

Root-knot nematodes are small eel-like worms which live in the soil and feed on plant roots. Root-knot nematodes cause serious damage to watermelons when planted to infested fields. All species of root-knot nematodes are capable of causing serious damage to watermelons. One reason nematodes are a major problem is that there is not a good easy-to-use nematicide for use on watermelons. Although fumigants do an excellent job in reducing nematode populations, the waiting period required after application causes too much delay in watermelon seeding. They impair the root system so the plant cannot take up water in nutrients, but moreover, they allow diseases like fusarium wilt to enter the plant. Serious root-knot injury is usually noticed by stunted, wilted growth in the above ground part with a galled root system becoming progressively worse during the growing season. Potential watermelon fields should be checked for root-knot before the crop is planted.

Root-knot nematode damage

Malformations

Blossom End Rot occurs more readily in oblong melons.   Caused by a deficiency in calcium either in the soil or by a lack of water availability for Ca uptake and movement.  Prevent by liming and providing adequate supply of water.    Hollowheart and Whiteheart Caused by genetics, environment, and culture methods (lack of water). Grow cultivars with low incidence with optimal nutrition levels and water quantity.     Sun scald Caused by sun hitting fruit surface directly.  Maintain good canopy for shading of fruit.  Do not allow harvested melons to lay by roadside for long periods before pickup.

Blossom end rot

HARVESTING
    Watermelons are non-climateric and therefore harvested by hand when they have fully ripened.  Ripeness is not easily determined for an inexperienced picker, but here are some helpful hints.

Check for:     1. A pale yellow ground spot     2. A brown melon tendril (see photo right)     3. A change in sound when thumped from a metallic ringing sound to a soft hollow sound.     4. A breakup of green bands at the blossom end of the fruit.     5. Development of ribbed indentations that can be felt with finger tips.

(photo provided by www.acesag.auburn.edu)

    The best way to determine maturity of an entire field is to randomly select melons from across the field and use a hand refractometer to measure the sweetness of the melon.  Soluble sugars should be 10% or more near the center of the melon.
    When harvesting, make sure that the melon is cut from the vine instead of pulled.  Pulling creates a cracking wound that pathogens can enter and quickly destroy the quality of the fruit, not to mention ruining the appearance of the fruit.  Leave the stems on the melon for as long as possible, and treat for stem end rot after picking.
    Harvesting is usually an 9-12 person job, with 1 truck driver, 2 stackers, 4-6 loaders, and 2-3 harvesters.  Ensure that the employees handle the watermelons in a manner that will not cause damage to the fruit.  Do not allow the melons to be tossed up onto the truck, nor allow workers to stand on the crop while sorting and loading.  Trucks, wagons, and crates should be padded and watermelons should be arranged to limit movement to protect from interior bruising.  Pack the watermelons in layers no more than 4 deep.

POST HARVEST

Optimum temperature for watermelon storage is 60°F.  The fruit can be stored for up to 2 weeks.  The relative humidity is not critical due to the thick waxy rind. For transportation, melons should be ventilated and kept at a temperature range of 55° to 70°F.  Be careful not to allow temperatures to approach 90°F, for the tissue begins to breakdown at this temperature.  Once sliced, watermelons should be wrapped in cellophane and stored at 32° F.  Do not store or ship with other fruits that emit ethylene.  This will cause over ripening and tissue breakdown. When shipping, recut and retreat stems for stem rot.     Melons can be marketed in fiberboard encased pallet bins that are easy to unload from the truck and consumers can easily pick fruit out of.

Some information and photos were obtained from Commercial Watermelon Production Cooperative Extension Service, The University of Georgia, College of Agriculture, Athens, Ga. 1988. B-996