Your growth our growth

Watermelon farming guide 101

our growth

www.facebook.com/greenlife.co.ke

www.twitte

DENNIS MUINDI

6/10/2014

Watermelon farming guide 101

www.facebook.com/greenlife.co.ke

www.twitter.com/greenlifeagro

DENNIS MUINDI

6/10/2014

Watermelon farming guide 101

WATERMELON FARMING

Watermelons, botanically called Citrullus lanatus belong to the family of Cucurbitaceae, they

originated in Africa. Watermelons grow large -- but how do you know when they are ready for

picking? With the many different types of watermelons and the many different sizes, it can be

confusing. There are some signs to watch for that can indicate your watermelon is fully grown.

We’ll show you how to grow and harvest watermelons here.

Planting Instructions

Watermelons prefer a hot, dry climate with mean daily temperatures of 22 to 30°C. Maximum

and minimum temperatures for growth are about 35 and 18°C respectively. The optimum soil

temperature for root growth is in the range of 20 to 35°C. Fruits grown under hot, dry conditions

have a higher sugar content compared to those grown under cool, humid conditions. The crop is

very sensitive to frost.

The length of the total growing period ranges from 80 to 110 days, depending on climate.

Spacing: Watermelon vines require considerable space. You can sow seeds in hills or rows.

Seeds are placed on hills spaced 1m x 1m and planted 2cm deep. One-two weeks after the

seedlings are established, thin to the best three plants per hill.

Soils: Plant watermelons in good, well-drained soil. The crop prefers a sandy loam soil texture

with pH of 5.8 to 7.2. Clay soils do not raise a good crop. Cultivation in heavy textured soils

results in a slower crop development and cracked fruits. If your soil is difficult, create raised

beds by adding organic matter to improve the drainage and aeration.

Fertilizer Requirements: Watermelons are heavy feeders. Add generous amounts of manure,

compost and leaves to your garden. Work the soil well. Make sure it drains well. Fertilize with a

phosphate fertilizer at planting, 3-4 weeks later, top dress with CAN for leaf development and 4

weeks after this, top dress again with NPK triple 17 for fruits and flowering. You may also apply

recommended foliar feeds for vegetative growth and flowering.

Micronutrients: Apply as determined by soil test. Micronutrients that should be tested for are

zinc, manganese and boron.

Watering: Watermelons need adequate water for productivity, though their requirements are

slightly lower than those of other vegetables. Plant stress from limited water availability will

cause them to stop growing and reduce fruit size and quality. All the same, be careful not to over

water. Excessive irrigation can reduce crop yields by leaching crop nutrients or promoting

disease, it can also cause fruiting plants to collapse from lack of oxygen. Watermelons have

extensive root systems and can obtain available ground moisture, thus reducing irrigation

requirements. Check the soil moisture regularly and water as necessary before the melons start to

wilt or go into stress. Allow the top 1” to 2” of soil to dry between watering.

Plant Development and Care: Maintaining a healthy plant is the first step in disease control.

This includes weeding, pruning and proper spacing to allow good air circulation, especially in

wet and humid weather. Sunlight- Watermelons need full sun and heat to grow healthy vines and

big fruit. Weeding- Watermelons are not good competitors and do not flourish if weeds shade

them or compete with them for moisture and fertilizer. Remove small weeds to avoid stunting or

stressing the melons. Avoid disturbing the root by cultivation as this weakens vines and keeps

them from producing fruit. Rotate planting locations and use resistant varieties to avoid pest and

disease accumulation.

Pruning - Remove deformed and melon fly-stung fruits. Deformed fruits result primarily from

water stress and/or insufficient pollination. These fruits are removed at an early stage in order to

obtain uniformly well-shaped fruits. In some instances growers remove well-formed fruits if

there are more than two or three melons already developing on the plant. Reducing the number

of melons per plant, concentrates the plant’s producing power in a smaller number of fruits,

thereby increasing size and perhaps quality.

Insects and Pests

Early use of insecticides is important. While constant scouting is crucial in controlling pests and

diseases, Fungicides can be effective if used early.

Major insect pests include aphids, melon fly and mites.

Powdery and downy mildews, anthracnose, alternaria leaf spot, gummy stem blight and

Fusarium wilt are some of the common diseases affecting watermelon. However, some cultivars

are resistant to some diseases.

Harvest Recommendations

It is difficult to tell if a watermelon is ripe by just looking; it must be examined. Watermelons

will not continue to ripen after harvest. For best quality, be sure to scout the crop daily so that

melons can be picked when they are at their best. Here are indications you can look for:

• Thump it: When thumped an immature melon will give a metallic “plank” and a mature one a

dull “plank”, if the harvester can determine the difference. This method should only be used

when the melons are cool; an immature melon will sound mature if it has become warm

throughout.

• Look at the color on the top. The fruit is ripe when there is little contrast between the stripes.

Another indication is when the surface color of the fruit turns dull.

• Look for the spot where the melon rested on the ground; a yellow or a cream-yellow colored

spot suggests ripeness and a white or pale green spot indicates immaturity.

• The curly tendril immediately opposite where the melon is attached to the vine will be brown

and withered when the melon is ripe.

Storage and Handling

Watermelons are not adapted to long storage. At low temperatures they are subject to various

symptoms of chilling injury and loss of quality, and at high temperatures they are subject to

decay. Between 10 and 150

C is a good compromise. Watermelons should be consumed within 2

to 3 weeks after harvest, primarily because of the gradual loss of crispness. Quality hybrids are

able to keep longer. Watermelons should not be dropped, thrown, or walked on, as internal

bruising and flesh breakdown will occur.

Fruit disorders

Blossom-end rot is caused by calcium deficiency and water stress. It is worse in hot, dry, windy

conditions where moisture stress is more likely to occur. Symptoms include young fruit drop and

brown rotting lesions at the blossom end of older fruit. Good water management and ensuring

sufficient soil calcium availability will usually address the problem. Soil or irrigation water

salinity may also promote blossom end rot. It tends to occur more readily in oblong varieties.

Watermelons having blossom-end rot are unmarketable. FERRARI SPRAY 80-100mls will

supply sufficient calcium to prevent the disorder

Internal cracking is caused by cool temperatures during early fruit-filling period. Other

influences are stop-start growth, excess nitrogen, low boron levels, or heavy infrequent watering

at fruit fill. Affected melons tend to be flattened in shape and feel lighter than usual.

Spongy end occurs in melons, which have been poorly pollinated. These melons may turn

yellow and drop off the vine early in their development or partly develop with the stylar end soft

and spongy. This area is also slightly pointed. Internally, there is very poor seed development at

the spongy end.

White heart is white streaks or bands of undesirable flesh in the heart (center) of the fruit. This

is caused by excessive moisture (and probably too much nitrogen) during fruit maturation.

Hollow heart is a disorder that varies among varieties. Causes are unknown.

Sunburn occurs most frequently in varieties that have dark green rinds. "Charleston Gray" types

and other melons with grey-green rinds rarely sunburn. Good healthy foliage will minimize

sunburn as well as favor good yields and quality. Strong winds can blow unprotected vines away

from the developing fruit along the edges of the rows and cause full exposure of the fruit to the

sun.

Rind necrosis is an internal disorder of the watermelon rind. Symptoms are brown, corky, or

mealy textured spots in the rind which may enlarge to form large bands of discolouration that

rarely extend into the flesh. Experienced pickers often can detect affected melons by the subtle

knobbiness that is visible on the surface of affected melons. The cause of rind necrosis is

unknown. Bacterial infection has been reported to be a cause, although similar bacteria are found

in healthy melons. Drought stress also is reported to predispose melons to rind necrosis

COMMON PESTS

Aphids (Aphis gossypii)

The cotton aphid (Aphis gossypii) is common on cucurbits, including watermelons. Colonies of

green to blackish aphids are found on tender shoots, mainly on the lower leaf surface, where they

suck sap. The growth of the attacked shoots is stunted and the leaves are curled and twisted.

Aphids excrete honeydew, which leads to growth of sooty mould, and may attract fruit flies.

Aphids, in particularly winged aphids, transmit virus diseases (e.g. cucumber mosaic virus) when

feeding from plant to plant.

Control: spray with EMERALD (imidacloprid) 10mls/20l

Whiteflies (Bemisia tabaci)

They suck plant sap and excrete honeydew where moulds grow, which may affect plant growth

and vigour. The tobacco whitefly is considered a major pest due to its ability to vector various

virus diseases, which cause considerable damage to watermelons and other cucurbits.

Control: spray with EMERALD (imidacloprid) 10mls/20l

Epilachna beetles (Epilachna chrysomelina, Henosepilachna elaterii )

Adults of this 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 cases. The larvae are 7-9 mm in length, soft and

covered with dark coloured spines. Adults and larvae feed on leaves leaving a fine net of veins.

Damaged leaves shrivel and dry up. Young plants can be entirely destroyed. Older plants can

tolerate considerable leaf damage. This beetle is a vector of squash mosaic virus. Epilachna

beetles attack all cucurbits.

Control: spray with PENTAGON (lambda cyhalothrin) 10-12mls/20l

Flea beetles (Podagrica spp.)

They are tiny to small (1.5 to 3 mm) long leaf beetles with well-developed hind legs. They are

named for their habit of jumping like fleas when they are disturbed. The colour of the adult

beetles varies from black, brown, black and yellow striped or metallic blue-green depending on

the species. Adult flea beetles chew small round holes (shot holes) in leaves, giving them a sieve

like appearance. This damage is usually seen only in plants that show extreme foliar stress

resulting from lack of water or powdery mildew. Seedlings are most vulnerable to flea beetle

feeding when stressed, particularly by inadequate moisture. Older plants can withstand

considerable leaf perforation.

Control: spray with PENTAGON (lambda cyhalothrin) 10-12mls/20l

Red spider mites (Tetranychus spp.)

Red spider mites attack leaves of watermelons. Adults are about 0.6 mm long. Attacked leaves

have a stippled appearance, turn yellowish to whitish and dry up. Often young plants are entirely

destroyed. In older plants growth can be severely stunted and the fruit set considerable reduced.

Spider mites can be a problem in dry and hot conditions. Plants under water stress (drought) are

more likely to suffer damage by spider mites.

Control: spray with BAZOOKA 10mls/20l

Melon fly

Control: Use PENTAGON at the rate of 15mls/20l

Cutworms and wire worms

Drench the planting holes with RANGER at the rate of 30mls/20l

Root-knot nematodes (Meloidogyne spp)

Symptoms of infestation by root-knot nematodes are similar in all crops: wilting of plants and if

infested plants are pulled from the soil the roots can be seen to be distorted, swollen and bearing

knots. The infested roots eventually rot and affected plants die.

Control: drench the planting holes with PLANTGUARD 200-500mls/20l

Diseases

Damping-off diseases (Pythium aphanidermatum)

They cause reduced plant stand (population). Diseased seedlings exhibit rotting and death of

infected roots. A white cottony growth appears on affected tissues. Loss of young plants occurs

through damping-off.

Control: Drench the planting holes with CHARIOT (carbendazim) at the rate of 30mls/20l

Powdery mildew (Sphaerotheca fuliginea and Erysiphe cichoracearum)

Symptoms first develop as a whitish talcum-like powdery growth on upper 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.

Apply KATERINA (chlorothalonil) on a preventive 7-10 day schedule at the rate of

40mls/20l.When powdery mildew appears spray MILESTONE(Azoxystrobin) at the rate of

15mls/20l

Angular leaf spot (Pseudomonas syringae pv. lachrymans)

Spots on leaves angular in shape and variable in size due to leaf veins that limit their

enlargement. Initially, spots are water-soaked. In moist weather, bacteria ooze from the spots in

tear-like droplets, which dry making the tissue white. Affected leaf dries and shrinks and it may

tear away from the healthy portion leaving irregular holes. Leaves approaching maturity are

more susceptible than older leaves. Fruits may also be attacked. Fruit spots are small, nearly

circular and superficial. The bacteria survive in association with seed. When infected cucumbers

are used for seed extraction, the seed can be contaminated during fermentation process. The

bacteria can also survive in soil or infected crop debris. Drainage water can spread the bacteria in

the soil. Angular leaf spot disease is favoured by wet conditions, frequently associated with

rainfall and overhead irrigation. Optimum temperature for disease development is 23.9 to 27.8º

C. The disease attacks watermelon, gherkin, muskmelon, pumpkin, squash, and vegetable

marrow.

Apply FOSET (Fosetyl aluminium) at the rate of 50gms/20l

Anthracnose (Colletotrichum graminicola) Symptoms are most noticeable on fruits. Spots on fruits are circular, black, and sunken. When

wet, the centres of the spots become salmon coloured due to a mass of fungal spores. Affected

fruits can be destroyed by secondary soft-rot organisms, which enter through broken rind. The

fungus is seed-borne. It can survive in crop debris and in weeds belonging to the cucurbit family.

Fungal development is promoted by wet conditions, high relative humidity and moderate

temperatures (20 to 23.9º C). Its host range includes watermelon, cucumber, gherkin, gourd and

muskmelon. Cucurbit weeds can also be attacked.

Apply MILESTONE (Azoxystrobin) 15mls/20l or KATERINA(Chlorothalonil) 40mls/20l

Fusarium wilt (Fusarium spp.)

In seedlings, the cotyledons lose their healthy look (luster) and wilt. This is followed by

complete collapse of the plants. Older plants initially exhibit wilting and yellowing of leaves

near the crown. Later individual vines and then the whole plant wilt and die. If the taproot and

stem are split open, an orange-brown discolouration of the water conducting tissues will be seen.

Fruits from affected vines are small with poor flavour and colour.

Drench the planting holes with CHARIOT (carbendazim) at the rate of 30mls/20l

Watermelon mosaic virus [Papaya ringspot virus-watermelon strain (PRSV-W), Watermelon

mosaic virus 2 (WMV-2)]

This virus is mechanically transmitted and also spread by several species of aphids in non-

persistent mode. It is not seed transmitted. Its host range is primarily restricted to cucurbits

although one of its strains infects peas.

The disease is transmitted by aphids and beetles. Apply PENTAGON 10-12mls/20l to kill the pests

NB: During sprays incorporate INTEGRA 2-3mls/20l to reduce surface tension and ensure

maximum spreading of pesticides

THE END