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Members of MDI and UoN at ICT introduction and training event in Kambu

What are watermelons?

Watermelons are large round fruits that thrive very well in dry lands. Some varieties have seeds while others are seedless. They are a good source of water in the diets of human beings but can also be used for making jams and other preservatives including jell preparation. They are also useful in flavoring summer drinks and smoothies. They are quite nutritious, for instance, one cup serving of watermelon can provide calories, vitamin C, vitamins A, B6, B1 and minerals such as potassium, magnesium, antioxidants among others. They can also be prepared as grilled watermelons as found in the case of watermelon stake which is commonly found in restaurants in certain countries.

Watermelon Varieties

Yellow watermelon
This variety has a yellow colored flesh and is said to be sweeter and more honey flavored than the red fleshed watermelon.

Orangeglo
This variety has a very sweet orange pulp, is large and oblong and weighs 9-14 kgs (20-300pounds). It has a light green rind with jagged dark green stripes and takes 90-100 days from planting to harvest.

The moon and stars variety
This variety has a purple rind and has many yellow circles (stars) and one or two large yellow circles (moon). It weighs 9-23kg and the flesh is pink or red and has brown seeds. The foliage is spotted and planting takes 80-85 days.

How do you plant watermelons?

Watermelons seeds can be planted directly in the field or indirectly through the nursery. In the tropics direct planting should be done between 20th April to15th May while nursery planting should be done between 1st May to 20th June. The seeds should first be grown in nurseries or containers and then transplanted through plastic mulch when the daily temperatures are 60degrees F.

Before field planting is done, one should lay clear plastic mulch since this would help in conserving moisture but also increases total early yield. The mulch could be black plastic or paper. Fumigation of the soil is also necessary to control weeds and soil borne diseases. Prepare the planting bed 30 days before actual field planting.
When applying fertilizer, at least 50% of nitrogen should be in nitrate form and should be applied during field preparation.

Spacing
The recommended spacing for watermelons is 6 to 8 feet between rows and 3 to 4 feet between plants in a row. For seedless varieties, you need a pollinator variety placed in every third row to ensure there is good fruit set.

Where are the potential watermelon markets in Kenya?

Domestic players such as Nakumatt are beginning to open stores in smaller towns outside the capital city Nairobi, whilst pan-African player Shoprite has been rumored to be considering market entry through the acquisition of struggling local player Uchumi. While the farmers deliver direct to Uchumi, the supply of indigenous vegetables to Nakumatt is done through traders who supply to its subsidiary company

There are several other local vegetable markets for water melons in Kenya. These include; supermarkets, Aghakhan market, city market, Kangemi market, Gikomba among others in Nairobi and other towns in Kenya. We also have a few export markets such as the South Africa one that imports watermelons and other vegetables from Kenya.

Fusarium Wilt

Seedling wilts and dies soon after emergence. Other symptoms include large roots and red colored inner tissue.
Cultural control – Crop rotation.

Downy Mildew

Yellowish to brown spots on the upper leaf surface. Loves wet temperatures so one should avoid overhead irrigation.

Damping off

Causes young seeds to wilt and die and is common in low temperatures / wet weather
Control – Broad spectrum fugicides

Anthracnose ( C lagenarium)

Symptoms include raised circular water soaked spots on crown leaves, yellowing color , kills leaves, dark sports on fruit.
Chemical control– Apply earl chlorotha lonil and azoxystrobin
Cultural control– use resistant varieties, Disease free varieties.

Alternaria leaf blight ( alternaria cucumerina)

The disease defoliates vines , reduces fruit yield, Size and quality. It attacks oldest leaves, show round water soaked lesions
Chemical control– Chlorothalonil
Cultural control– Resist varieties , crop rotation , remove or burn crop debris

Watermelons - Common Pests

The most common pest that affects watermelons is the spider mites which thrive in the hot, dry season and the aphids which are common after cool seasons. Others include seed corn maggots, melon worms, cutworms, leaf miners, cabbage loppers and cutworms.

Aphids

Feed on plant saps reduce vigor size and field feed under leaves, extract honey dew, lead to growth of black sooty vector plant virus e.g. Cucumber mosaic virus.
Chemical control – Phimetrozine
Biological control- using natural enemies such as lady beetles, wasps
Cultural – Use resistant cultivars, avoid barriers like hedgerows or woodlots which encourage aphids falling in field.

Cabbage Loppers

These are pale green with thin white stripes on back and sides. Feed on underside of leaves produce ragged holes. Use chemical Bacillus thuringiensis as a form of control.

Cucumber Beetles

These eat leaves and stems and blossoms of developing plant and transmit bacterial wilt disease.
Chemical/ Biological control: azinophos methyl
Cultural control: use resistant varieties, cultivate thoroughly before planting, use plastic or straw as bedding , reduce weeds.

Melon Worm

These feed on leaves and flower buds, vines and fruits.
Cultural control: After harvest remove debus from field, destroy vines and unused fruit and control weeds.
Chemical control: Abamectin and Carbaryl.

How to harvest a watermelon

Harvesting should be done in the middle of July to August. When harvesting, cut melons from the vine and avoid pulling, twisting or breaking of twigs because pulling provides room for entry of bacteria and fungi that causes souring or decay of inner flesh.

How do you know a watermelon is mature?

There are a number of signs which can be used to tell whether watermelon is ripe or not. Maturity however depends on location, variety and plant growth. To check whether a watermelon is ripe, one could use the following indicators;

• Tendrils or pigtails on vines nearest the fruit are wilting and have changed color from green to brown.
  
• The ground spot on the belly of the watermelon has changed from white to light yellow.
  
• The thumbing sound changes from a metallic ringing when immature to a soft hollow sound when mature.
  
• The green bands on stripped varieties gradually break up as they intersect at the bottom of the watermelon.