Water melon

Land Preparation of Watermelon

Watermelon does well on sandy loam soils which are well drained and slightly acid. Ideal pH is 6-7. When planted on very heavy soils, the plants develop slowly, and fruit size and quality are usually inferior.

1.1. Propagation

Watermelon is propagated by seeds, directly planted in the field or by transplants, instead of planting directly in the field and have 3 weeks of accumulated weeds germination and insect attacks to battle with, planting of seeds in seed trays or pots in a protected area for later transplant into the field when at least 2-4 true leaves have developed (4-6 weeks after sowing), is a very viable option. The seeding rate is 0.5 kg/ha.

3.2. Fertilisation

Watermelon has moderate nutrient requirements compared to other vegetable crops, and because of its deep rooting, it is efficient in extracting nutrients from the soil. In general, the fertilizer recommendation is 90:60:60 kg of N:P:K/ha. However, watermelon can be grown with little or no fertiliser after heavy fertilizer crops have been harvested.

Planting of Watermelon

Watermelons are grown throughout the year in lowland areas but peaks of rainy season should be avoided. The holes are dug at a distance of about one meter within the row and about 2 meters between the rows. Plant 2 seeds per hole, placing them 3 to 4 cm deep into the soil.

Crop management of Watermelon

1.1. Weeding and mulching

Watermelon does not require deep intercultural operation. The field may be made weed free by intercultural operations like hoeing and earthing up along with top dressing of fertilizers. Mulching is very useful in preventing the fruits from touching the ground.

1.2. Pollination

Watermelons produce separate male and female flowers. Male flowers are produced initially, followed by production of both sexes usually at a ratio of 1 female to 7 males. Watermelon flowers are viable for only one day hence important to have pollinating insects.

1.3. Irrigation

Although watermelon is a deep-rooted crop able to tolerate a significant degree of soil moisture stress, peak production requires timely irrigation. After crop establishment (either by seed or transplant), irrigation may be withheld for a period of several weeks to encourage deep rooting.  However, irrigation should be managed to minimise water stress throughout the fruit set and fruit-sizing periods. Water stress during early fruit development can result in small, misshapen fruit and the occurrence of blossom-end rot (a physiological disorder in which the blossom end of a fruit ceases to grow and becomes dark and leathery). As harvest time approaches care must be taken to avoid large fluctuations in soil moisture content, as heavy irrigation (or rainfall) can result in fruit splitting. Irrigation should be reduced or stopped 7 to 10 days prior to harvest.

1.4. Vine and fruit pruning

Pruning of plants by removing excess shoots (3-4 main shoots) increases yield and quality of fruits. The following method is followed: “The main vine is pinched off after 5 leaves (at 5-7^th node). Then almost 15 days after pinching, three to four (3-4) vines are maintained but only 2-3 vines are allowed to have fruits on tertiary vine arising from secondary vine); the remaining vine  which is not allowed to have fruits will support the other 2-3 vines to feed their fruits”. To avoid disease spread, do not prune melons when vines are wet.

Thinning of fruits to 2-3/vine results in good sized fruits. Remove malformed and blossom-end rot fruits as and when noticed so as the remained fruits develop properly.

Pests and diseases management of Watermelon

1.1. Fusarium wilt

Watermelons are attacked by Fusarium wilt at all stages of development. Seeds may decay in the soil. Seedlings wilt collapse and die before or after emergence. Older plants wilt, wither, and die any time during the growing season. If melons do form, they are generally small and unpalatable. Wilting of runners usually progresses slowly, showing initially during the midday heat. Such plants recover at night, but after a few days they wilt permanently and die.

Management:

• Use resistant varieties, if available;
• Use disease-free seeds;
• Avoid spread of the fungus through contaminated farm implements and furrow irrigated water.>

1.2. Anthracnose

Anthracnose is a very destructive disease of watermelons and other curcubits. Anthracnose attacks all above-ground parts of the plant. Watermelon can be infected at any stage of development; however, disease symptoms are first noticed as round to angular reddish brown spots on older 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.

Management:

• Use certified disease-free seeds;
• Treat own seeds in hot water for 20 minutes at 43° C ;
• Plant resistant varieties, if available;
• Practice crop rotation with non-cucurbits;
• < Destroy volunteer cucurbits in the field.

1.3. Powdery mildew (Erysiphe cichoracearum and Sphaerotheca fuliginea)

Symptoms first develop as a whitish talcum-like powdery growth on lower leaf surface. The powdery growth is composed of fungal spore mass. These areas covered by white powdery growth may enlarge and join up to cover both lower and upper leaf surfaces. Severely affected leaves dry, turn brown and become brittle. Vines can be also attacked. Secondary effects of the disease include sun-burning and premature ripening of fruits.

The powdery mildew fungi are influenced by plant age, humidity and temperature. Foliage is most susceptible 16 to 23 days after unfolding. The fungi reproduce under dry conditions. Infection increases as humidity increases, but does not occur when leaf surface is wet. Optimum temperature for infection is about 27.4º C. However, infection can take place at a temperature as high as 32º C and relative humidity as low as 46%.

Management:

• Use resistant varieties, if available
• Spray with sulphur based fungicides, which provide good control
• Destroy weeds belonging to the cucurbit family

1.4. Downy mildew (Peronospora cubensis)

Symptoms on leaves appear as small, pale-yellow areas on upper leaf surface. Under humid conditions, a purplish, grey whitish growth may be seen on the underside of the yellowish spots. Affected leaves curl, shrivel and die.

Most downy mildew fungi require cool weather for reproduction and development. This is not true of the cucurbit downy mildew fungus. Optimum temperature for infection is at 16 to 22º C.  It can survive when temperatures are over 37.8ºC. The most critical factor for infection is a film of moisture and / or long dew periods on leaves.  Disease spread is primarily thorough by wind and rain splash. The fungus attacks only members of the cucurbit family, mostly those that are cultivated, although it can infect wild cucumber and a few other weed hosts.

Management:

• Use resistant varieties, if available;
• Leave wide spacing between plants;
• Avoid overlap cucurbit plantings;
• Copper fungicides at 0.1% can provide control.

1.5. Watermelon mosaic virus

Caused by two distinct viruses referred to as Watermelon Mosaic Number I and Watermelon Mosaic Number II. The most common symptom is mottling of the leaf, some plants are stunted with abnormally shaped leaves. The diseases is usually spread by aphids which can spread through an entire planting during the growing season.

Leaf symptoms include a prominent light and green mosaic pattern, mottling (yellow with green islands or blisters), and in severe cases, leaf distortion whereby affected leaves appear fern-like. Diseased fruits are malformed (slightly to severely misshaped with wart-like lumps).

Management:

• Use tolerant / resistant varieties if available;
• Remove infected plants (disinfect hands and tools with 70% alcohol after contact with infected plants);
• Do proper weeding
• Control insect vectors. A sustainable approach of controlling aphids is important to prevent aphids reaching the crops and transmitting virus.

1.6. The Epilachna beetle (Epilachna chrysomelina)

Adults of the Epilachna beetle, also known as the African melon ladybird are 6-8 mm long, reddish in colour with a number of black spots on the wing covers. The larvae are 7-9 mm in length, soft and covered with dark coloured spines. They pupate on leaves. Both adults and larvae feed on the leaves leaving a fine net of veins.

Damaged leaves shrivel and dry up. They may also gnaw (chew) stems and eat holes in fruits. These beetles are most likely to be a problem during establishment when plants are small, young plants can be entirely destroyed. Older plants can tolerate considerable leaf damage, but during flowering fruit set maybe affected. This beetle is a vector of squash mosaic virus. The Epilachna beetle attacks all cucurbits. They often fly into a crop from nearby crops.

Management:

• Do not grow any cucurbit near crops attractive to the Epilachna beetle (e.g. other cucurbits, potatoes, maize)
• Whenever necessary apply neem products. Simple neem-based pesticides are effective controlling this pest.

1.7. Fruit flies (Bactrocera cucurbitae, Dacus spp  and Ceratitis capitata)

Fruit flies are important pests of cucurbits. They pierce the fruits and lay eggs in them. The fruit fly maggots feed inside the fruit causing sunken, discolored patches, distortions and open cracks. These cracks serve as entry points for fungi and bacteria, which cause fruit rot.

Management:

• Avoid continuous cultivation of cucurbits at the same place.
• Destroy all infested fruits.
• If possible, wrap or bag individual fruits with newspaper or paper bags to prevent fruit flies form laying eggs on the fruit. Wrapping or bagging should be started shortly after fruit set.

Harvesting of Watermelon

Harvesting usually begins 3-4 months after planting. Change in the colour of the portion of the fruit which rests on the ground from white to creamy in case of light skin colour, or to yellow in case of dark skin colour, is a useful guide of maturity. A metallic sound when the fruit is tapped with the back of hand or with fingers denotes immaturity, whereas a heavy dull sound indicates ripeness. The drying of tendril at the base of the fruit is also a sign of maturity. The average fruit yield varies from 20 to 25t/ha and may go beyond 30t/ha in some high-yielding varieties/hybrids.

Post harvest processing of Watermelon

Watermelon requires careful handling ( picking and transport) and they can be stored for maximum of 2-3 weeks in a cool place.Watermelon is eaten raw or processed into juice either alone or blended with other fruits, yoghurt, watermelon syrup watermelon spread, watermelon sweets. etc