Melons are vining crops that require a lot of space, especially watermelons. For this reason they are not well suited to small gardens and should be grown only in lot-size gardens in urban areas or larger gardens in rural areas. Melons can be grown in small gardens if the vines are trellised and the fruit is supported.
Secondly, the site for watermelon must have enough sunlight. Remove all shade plants; the soil must be fertile with good organic matter content. Melons grow best on a deep, well drained, sandy or sandy loam soil with plenty of organic matter. Heavy soils with a lot of clay often cause small, weak plants that produce fewer melons. Melons prefer soils with a neutral pH, and if the soil is too acidic the plants will drop their blossoms.
Watermelons grow and produce fruits ideally during dry, sunny periods. Excessive rainfall and high humidity reduce productivity by affecting flowering and encouraging the development of leaf diseases. Elevations up to 1,000m normally provide suitable conditions for growth although excessively high temperatures of more than 300C may be harmful, reducing the degree of fertilization. Stable day-night temperatures promote a rapid growth rate.
Clear the land of all vegetation covers and plant debris. Spray a systemic herbicide (Glyphosate) to control noxious weeds such as spear grass, etc. Prune trees; remove other shrubs that could impose shade. Plant residue need not be burned as they could be used as mulch material. Conservation tillage is best for watermelon especially when the soil is of sandy loamy texture class. But in cases where the soil texture is clayey, a little ploughing and harrowing may be necessary to facilitate deeper rooting and moisture penetration.
Watermelons grow best on non-saline sandy loam or silt loam soils. Light-textured fields warm up faster in the spring and are therefore favored for early production. Very sandy soils have limited water-holding capacity and must be carefully irrigated and fertilized to allow for high yield potential. Clay soils are generally avoided for watermelon culture, but they can be productive if irrigated with care to prevent prolonged saturation of the root zone (a condition that favors the development of root rot pathogens) and to allow good drainage between irrigations.
If organic matter or manure is added, it should be well composted. Apply manure or compost at 50 to 100 pounds (23kgs to 45kgs) per 1,000 square feet, or about 2 to 4 tons per acre, to build the organic matter content of the soil. Turn the soil over so all organic matter is covered completely.
Since melons require well-drained soils, work the soil into ridges or hills 4 to 8 inches high and 12 to 14 inches wide for planting. Heavier soils require higher ridges.
Place the rows of irrigated watermelons 10 to 12 feet apart, and rows of un-irrigated watermelons 12 to 16 feet apart.
Selecting the best watermelon variety is the most important decision made by a producer. Planting a variety that is not suited for the available market and the particular production situation leads to lower profits or possibly crop failure.
In addition to market acceptability, a variety must have acceptable yield, be adapted to the production area, and have the highest level of needed pest resistance.
Buy hybrid watermelon seed from the seed store. This guarantees good taste, good fruit sizes, and disease resistance that conform to varietal specification.
Do not use seed from previous watermelon fruit as such will produce crops with low yield, reduced sweetness, and disease susceptibility.
The seed of triploid watermelons is notoriously sensitive to very specific conditions during germination, as the tiny embryo is contained in a relatively large, hard seed coat. Temperature and moisture control is crucial to success, and too much moisture during germination can kill the seed.
Due to the higher seed cost, and since the outside climate is very difficult to control or predict, it is highly recommended to have seedlings made by a reputable nursery.
A farmer needs about 500gms of watermelon seeds per acre.
Seedlings must be transplanted and watered as soon as possible after they have been obtained from the nursery. Planting trays should be kept cool and moist in the shade until used. When transplanting, roots should not be damaged by application of unnecessary pressure around the root module. Soil should be watered into contact with the roots rather than pressed in.
Start the water melon seeds in the ground, right where they are supposed to grow. They do not like transplanting and so not necessary to put the seeds in a nursery bed. Put enough manure to the soil before planting and plough to mix well with the soil. 1 table spoon of DAP (Diammonium phosphate) should be put in every hole and properly mixed with the soil to make sure that the fertilizer does not burn the seed. DAP (Diammonium phosphate) contains phosphorus and helps the crop with root development. Always fertilize the soils after every three to four weeks with CAN (Calcium ammonium nitrate) also known as nitro-limestone which helps to fix nitrogen in the soil. Watermelon fruit grow well in soils with alkaline pH. It is therefore wise to add lime to the soil to maintain an alkaline pH. This tough should be done at intervals of 3years. Watermelon germinates in 7 days and the first fruits are seen from day 30.
Plant the watermelon seed with a spacing of 2m between rows and 1m between the holes where the seeds are to be planted. If there is not enough rainfall, water regularly to keep the soil moist. It is best to have a watering schedule if using irrigation because the fruit becomes stressed when the pattern changes and this affects the fruit development and the spray program.
Dig holes of 45cm wide, 45cm length and 30cm deep. Mix top soil with 2 spades full of manure and fill the hole leaving a space of 15cm. Sow two seeds per hole. Watermelon vines require considerable space.
Two crops can be planted in a year. Plant the first crop with the first or second rain, which occur mostly around February or early March (at this time moisture is not so much; as the plant establishes, the moisture increases into the growing season). The crop sown at this time will hit the market between May and June.
Plant the second crop in September (at this time, the moisture is reduced as the season is gradually folding out). The crop planted at this time will hit the market around December.
Watermelon has long taproot and it does not transplant well that is why it is better to sow the seeds directly in a pot. Sow 3-4 seeds directly in a pot once the temperature starts to reach 650F (190C) and above in the dry season. The germination takes place within 6 to 10 days. Thin out and leave only one of the strongest seedlings per pot.
Growing watermelon in containers is not much difficult though tricky. You need to understand the basics. As watermelon has long taproot choosing a deep pot is essential. A large pot or bucket that is at least 2 feet deep and half wide is required.
Watermelons should be grown in a sunny position. If you are growing it on a balcony or on a roof garden where space is tight, growing watermelon vertically on a trellis is a solution. Trellis should be minimum 4 feet tall and sturdy enough to carry the weight of melons.
Temperature
Watermelons are warm weather annuals but they can be planted in both tropical and temperate regions easily. It is possible to grow watermelons in temperature around 50-950F (10-350C). The optimum growing temperature is around 65-850F (18-300C).
Sandy and loamy soil is suitable for growing watermelons. Ideal soil pH is around 6-6.8. Avoid compact, clayey soils. Airy and well-drained substrate promotes the growth of the plant. Also, application of the well-rotted horse, rabbit or cow manure improves the texture of soil and provides nutrients constantly.
Watermelon requires a lot of water. Keep the soil evenly moist but not wet, the water must drain freely from the bottom. When growing watermelon in containers, you’ll need to water the plant every day and sometimes twice in a warm day. Once the fruits start to swell up and mature, reduce the watering. In that period, water carefully and moderately. Avoid overwatering and under watering both to get the sweetest melons.
It is important to weed the land to remove weeds that compete for water and nutrients with the plant. It can be done the 2nd or 3rd week after germination using herbicides or hoe.
If not controlled continuously, weeds can reduce watermelon quality and yields. Weeds compete for sunlight and moisture and create conditions favorable for disease and insect growth.
Weed control consists of hand weeding, mechanical cultivation, and the use of herbicides. Increasingly, growers are using black plastic mulch and herbicides as a weed control method. Plastic mulch controls weeds within the rows, while herbicides are used for weed control between the rows.
Apply pre-emergence herbicide prior to or within 12 hours of planting.
Several brands of pre-emergence herbicides are available to control germinating broadleaf weeds and grasses in seeded watermelons if used properly. Herbicides are economical when used appropriately. The following herbicides are commonly used in Uganda.
Shallow mechanical cultivation or hoe weeding are needed to control weeds before the vines start trailing. Pruning roots and vines with cultivating equipment slows melon development and reduces yield.
Watermelon vines should be mulched to keep down the weeds and conserve moisture, but the mulch should not be applied until the soil is thoroughly warm. In the meantime, keep the area clean with shallow hoeing. Straw, hay or chopped leaves are the best mulching materials to use.
Spread them in a six-inch mulch over the entire watermelon patch and draw the mulch up to the base of the vines. This should be done before fruits begin to form, because the small fruits may be damaged by handling. The best time to apply mulch is right after a rain, when the soil is thoroughly damp.
Insect Identification and Control
Treat fields previously in sod (the surface of the ground, with the grass growing on it; turf) or fields with heavy infestations of weeds in the previous year with a soil applied insecticide at planting to control soil insect pests including cutworms.
Seedling plants are extremely susceptible to feeding damage from adult striped and spotted cucumber beetles; you may need to treat plants with a foliar applied insecticide to prevent complete defoliation.
Aphids
Aphids are soft-bodied (usually wingless) insects that feed on the undersides of the leaves with their piercing-sucking mouthparts. The leaves of plants curl downward as the aphids suck the plant sap. Heavy populations cause plants to turn yellow and wilt.
Aphids secrete a substance known as “honeydew,” which collects on the surface of the lower leaves. Under favorable conditions, honeydew promotes the growth of sooty mold, a fungus that blackens the leaf surface. Sooty mold reduces the plant's ability to photosynthesize, thereby reducing melon quality and/or yield. Aphids also transmit several viruses that can reduce melon quality.
Aphid Control Measures
Cucumber Beetles
Cucumber beetles feed on the stems and leaves of young watermelon plants and transmit bacterial wilt disease. Bacterial wilt is one of the more damaging diseases of watermelons. Cucumber beetles can be controlled with foliar insecticides.
Red pumpkin Beetle
In watermelon, it makes holes in the cotyledons (first leaves of the seedling) and the young seedlings die.
Control: Dusting the plants with 1% Lindane or spraying Carbaryl (4g/liter of water) or Metacid (1ml/liter of water) during the seedling stage effectively controls the pest.
Cutworms
Cutworms feed on young seedlings or developing melons.
Damage to the melon is often confined to the rind. Rind damage may be superficial.
Inspect fields during land preparation and just before and during the planting operation. Treatments should be made either by incorporation of a soil insecticide or a directed spray if plants are already present.
Melon Fly
This is the major pest of watermelon. The damage by maggots results in rotting of young and ripened fruits or drying and shriveling of fruits before maturity. Maggots of this fly causes severe damage to young developing fruits. Fruit flies are usually a problem as soon as female flower initiation takes place.
Management: The affected fruits should be regularly pinched off and buried in a pit. Place 3 Para Pheromone traps per acre to attract and trap male fruit flies. Spray with recommended fungicides.
Spider Mites
Spider mites are very small spiders found on the undersides of the leaves.
Mites reproduce very rapidly, completing a life cycle in five days when the temperature is 75o F or above. As a result, they can become very numerous in a short period of time.
Mites feed by sucking sap from the plants, and if present in large numbers, they stress the plant, reducing vigor and eventually yield. Mites reproduce most rapidly during hot, dry weather. Mites can be controlled with: miticide sprays; cutting and burning of severely infested plant parts reduces further multiplication of mites. Ensure proper ventilation, irrigation and clean cultivation.
Rind worm
Rind worm refers to any worm that attacks the rind of the melon, the most common of which are cutworms, corn earworms, loopers, beet worms, and armyworms. When rind damage occurs, it is important to correctly identify the culprit and treat for that specific insect.
Thrips
Thrips are very small, spindle-shaped insects that reach a maximum length of 1/10-inch. Certain thrip species cause early foliage damage, while others are present during the period of heavy fruit set. Thrips damage plants by rasping the leaf surface during feeding. Severe damage usually occurs only during periods of slow growth. Damage is quickly outgrown when the plant is growing rapidly, and usually no treatment is required. If treatment is necessary, thrips can be controlled with foliar insecticide applications.
Nematodes
Root knot nematodes are small, eel-like worms which live in the soil and feed on plant roots, impairing the plants' ability to take up water and nutrients.
Moreover, they allow diseases like fusarium wilt to enter the plant. Serious root-knot injury results in stunted, wilted growth, a galled-root system, and reduced yields.
Root knot nematodes remain a major problem in commercial watermelon production because there are no easy-to-use nematicides. Applying fumigants effectively reduces nematode populations, but the waiting period after application often delays seeding until after optimum planting dates.
Below are some of the animal pests that affect watermelons:
(a) Field mice and rats: These can cause major problems in melon crops prior to emergence because they dig out and eat large quantities of seed. If this occurs, you may need to replant the crops several times, resulting in delayed harvests. You can reduce losses by pre-germinating seed or planting container-grown seedlings. The fungicide thiram, when used as a seed treatment, is a good repellent against mice and rats.
(b) Deer: Deer like watermelons, particularly as the fruit becomes ripe. Damage inflicted by these animals usually is less extensive. They may make holes in the rind and scoop or chew some of the inside of the flesh, but they do not usually consume an entire melon. Deer hoof prints look like two elongated tear drops that almost meet at the tip to form an upside down heart shape.
(c) Crows: Crows can be a devastating and annoying pest. Just before harvest, they can make melons unsaleable by punching holes through the skin with their sharp beaks. Often they damage many melons, and populations of crows can wipe out an entire crop in just a few days. Crows can be deterred with a sound device, such as a gas gun or bird alarm.
(d) Monkeys: Monkeys are really a pain somewhere quite far from the neck! They can cause enormous damage to the fruits and hence result into huge losses.
(e) Wild hogs: The feral hogs will consume the watermelon fruits, seeds, leaves and the stems. As a result huge loses can be caused by these creature. Control can be by use of wire mesh fence around the garden.
Fences are one of the best deterrents against deer, but they are not 100 percent foolproof. For best results, use a wire mesh with openings of less than 4-by-6 inches and make the fence at least 5 feet tall.
Brightly colored windsocks will discourage bird invaders, or you can stretch strings across your watermelon patch and attach aluminum pie plates or strips of aluminum to ward off birds during daylight hours, when they are most active.
Diseases that affect watermelons are similar to those of pumpkins.
A preventive program that combines the use of cultural practices, genetic resistance, and chemical control as needed usually provides the best results.
Many of the fungal, bacterial, and nematode pathogens survive in old crop debris and in soil. Rotate fields with non-cucurbit crops for at least three years to reduce pathogen levels.
Below are the common watermelon diseases:
Bacterial Fruit Blotch
Bacterial fruit blotch is a relatively new watermelon disease. It is thought to be a seed borne disease. The symptom of bacterial fruit blotch of watermelon is a dark olive green stain or blotch on the upper surface of the fruit.
The blotch is first noticeable as a small water-soaked area, less than 1 cm in diameter, but it rapidly expands to cover much of the fruit surface in 7-10 days. As the blotch increases in size, the area around the initial infection site becomes necrotic. In advanced stages of lesion development, the epidermis of the rind ruptures, and frequently a transparent or amber-colored substance is exuded.
Fruit lesions rarely extend into the flesh of watermelon, but when this occurs, the bacteria contaminate the seeds. Secondary rotting organisms are responsible for the ultimate decay and collapse of the fruit. Rapid expansion of fruit lesions usually occurs during the few weeks prior to harvest. Bacterial fruit blotch also affects melon, often resulting in water-soaked pits on the fruit surface, but the disease is best characterized in watermelon.
The fruit blotch bacterium also infects leaves, although foliage surrounding infected fruit may appear healthy to the untrained eye. Leaf lesions are small, dark brown, somewhat angular, and often inconspicuous. During periods of high humidity, the margins of leaf lesions often appear water- soaked. The initial symptom on seedlings is a water-soaked area on the undersides of the cotyledons.
As the cotyledons expand, the lesion becomes necrotic and often extends along the length of the midrib. Lesions on young true leaves are small and dark brown and may have chlorotic halos. Seedlings infected with fruit blotch often do not collapse and die in the greenhouse, but the incidence of foliar symptoms will increase slowly in a warm, moist environment.
Bacterial Wilt
Bacterial wilt causes runners to wilt, and eventually causes the entire plant to die. It is transmitted by cucumber beetles feeding on the young watermelon plant. Prevention consists of controlling cucumber beetles with foliar insecticides.
Anthracnose
Anthracnose, caused by the fungus Colletotrichum orbiculare, is a common postharvest watermelon disease. Dormant infections may exist at the time of harvest, with no external evidence of the disease. During storage, the latent infections may become active at high temperatures or after exposure to chilling injury inducing conditions. Disease development is rapid at temperatures between 20°C to 30°C (68°F to 86°F). The fungus can penetrate the fruit surface and wounding is not necessary for infection. Symptoms of anthracnose include sunken spots on the rind, which eventual become black. Red or orange colored spores may appear in the decayed areas.
Anthracnose spores are spread by water, insects, or pickers’ hands. Infection is particularly severe after prolonged wet periods. A combination of seed treatment, crop rotation, removal of infected debris, and fungicide applications are necessary for controlling this disease. Protective spray applications of the fungicide chlorothalonil should be made when vines start to run and should be continued at 7 to 10 day intervals during periods of humid or rainy weather. Also, storage of the fruit at 10°C (50°F ) will retard the growth of this fungus.
Damping-Off
Damping-off is a seedling disease in which the stems of young plants rot at the ground level and die. Damping-off is most serious in the presence of cool, wet weather, which retards rapid seedling emergence and early plant growth. In some years, the disease can reduce stands by up to 50 percent, while in other years, losses are very rare. Seed treatment and the use of cultural practices that encourage young plant growth are essential in preventing damping-off.
Downy Mildew
Downy mildew, a fungal disease, attacks the leaves of watermelon plants, causing lesions and wilting. Under conditions favoring the spread of downy mildew, an entire field may become infected. Downy mildew is not a problem in every year, but growers must monitor their plantings frequently for signs of the disease. Downy mildew can be controlled with fungicide sprays; Remove old plant debris. Do not overcrowd plants; avoid overhead irrigation, water plants through furrows.
Powdery Mildew
Powdery mildew also affects only the leaves, causing white, powdery mold on the leaf surfaces. Powdery mildew can be controlled with fungicide sprays; Remove old plant debris. Plant in sites with good air circulation and sun exposure; do not overcrowd plants.
Watermelon Mosaic Virus
Watermelon mosaic virus is an aphid-transmitted disease that causes plant stunting; a bumpy, mottled appearance on the fruit; and reduced yields. Extended high temperatures promote development of this disease.
Gummy Stem Blight
Round or irregular brown lesions with faint concentric rings on cotyledons; brown or white lesions on crown and stems; soft, circular brown lesions on fruit; lesions on stems and fruit may be oozing an amber coloured sticky substance. Fungus can be spread infected seed, air currents or water splash; Survives on plant debris in soil; Disease emergence is favoured by warm, wet conditions.
Rotate crops every 2-3 years to a non-cucurbit to reduce disease build up in soil. Spray:
Mancozeb, Copper Oxychloride, Chlorothalanil, Mandipropamid
Fusarium is a soil-borne fungus that attacks the roots, stems, and fruit of watermelons. The fungus can attack both sound and wounded tissue. Fruit symptoms first appear as spots on the underside of the fruit, and eventually spread to the upper surface. Infected tissue is usually spongy or corky. Under humid conditions, the fruit may become covered with a white or pinkish mold.
Decay may be shallow or it may extend deep into the flesh of the fruit. There is usually a sharp separation between healthy and rotted tissue. The temperature range that favors Fusarium growth is 22° to 29°C (72°F to 84°F). Use of resistant varieties can minimize the risk of Fusarium. Rotating the planting site and removing and destroying all plant debris at the end of each growing season will also reduce the incidence of the disease. For watermelon, a minimum eight-year planting site rotation is recommended to avoid Fusarium. This disease may also be spread by planting previously saved seed that came from contaminated fruit.
Stem-end Rot
Stem end rot is caused by the fungus Lasiodiplodia theobromae. The disease is first seen as a shriveling and drying of the stem followed by browning of the area around the stem, which progressively enlarges as the disease develops.
The cut flesh is noticeably softened and lightly browned. If the cut melon is exposed to the air for a few hours, the diseased areas become bla