Being a warm season crop, the plant requires ample sunshine and dry weather for production of fruits. In case they are grown in places where winter is prevalent, then they must be provided with adequate protection from cold and frost. They are extremely sensitive to the slightest of frost and hence care must be taken to keep the frost away from the crop. 24-27⁰C is ideal for the seed germination and growth of watermelon plants. A cool night would ensure ample development of sugars in the fruit.
Watermelons grow best in sandy loam soil that drains easily. It also grows well in black soil and sandy soil. However, they must have a good amount of organic content and must not withhold water. Water must easily drain off from the soil else the vines are likely to develop fungal infections.
pH for Watermelon Cultivation
The pH of the soil must be between 6.0 and 7.5. Acidic soil would result in withering away of the seeds. While soil with a neutral pH is preferred, it can also grow well even if the soil is slightly alkaline.
Watermelon is a dry season crop and it must be planted with irrigation. The watermelon beds are irrigated two days prior to sowing and then again 5 days after sowing the seeds. As the plant grows, irrigation is done on a weekly basis. Attention must be paid to water stress at the time of irrigation since it can lead to fruit cracking. While irrigating, water must be restricted to the root zone of the plant. Wetting of vines or other vegetative parts must be avoided especially during flowering or fruiting time as wetting can lead to withering away of the flowers, fruits or even the plant as a whole. In addition, wetting of the vegetative parts can also lead to development of fungal diseases. Moisture must be maintained near the roots so that the plants develop taproot system. As the fruits near maturity, irrigation frequency is reduced and it is completely stopped during the harvesting stage. This helps in developing flavor and sweetness in the fruit.
Crop Rotation with Watermelon
Owing to the risk of developing various diseases, watermelon is grown on the same soil only after a period of 3 years. It is usually rotated with paddy or with vegetables like tomato, chillies, etc.
Watermelon Planting Material
Watermelons grow from seeds. However, it is advisable to sow the seeds of watermelons bought from trusted place. There are different varieties of watermelon in India yielding a good harvest such as Vandana, Kiran, Sugar Baby, Watermelon Sultan, Improved Shipper, Madhubala, Arjun, etc.
The land is ploughed until the soil becomes very fine tilth. The land is then prepared according to the type of sowing to be done. Watermelons are generally seeded directly in the farms. However, in case it has to be protected from frosts, then it is seeded in nurseries or greenhouses and later transplanted into the main field.
It is sowed during the months of February to March in North India and then during November to January in west and North East India. The seeds are sown at a depth of 2-3 cm from the top soil.
- ‘Sugar Baby’: 80 days to maturity. Produces 10-pound melons with bright red flesh. This variety of smaller fruit can be planted just 4 feet apart.
- ‘Sweet Beauty’: 80 days to maturity. A 2004 All-America Selection. Bears 6-pound, oblong melons with red flesh.
- ‘Golden Midget’: 70 days to maturity. Bears petite, yellow-skinned 3-pound melons with pink flesh. Good for Northern gardeners.
Weeding is needed only in the initial stages of watermelon growth. Being a vine, use of herbicides must be done very carefully else the healthy plants may get affected. The first weeding is done about 25 days after sowing. Subsequently, weeding is done once a month. Once the vines begin to spread, weeding is not necessary as the vines take care of the weeds.
Diseases and Plant Protection
Watermelon is affected by numerous diseases such as aphids, thrips, anthracnose, mildew, wilt, etc.
Nature of Damage
This disease occurs wherein there are frequent rains and hence a high relative humidity. It also occurs when the moisture content in soil is high. The affected plants have a stunted growth. The fruits produced by such plants do not mature and hence have a poor taste.
- Yellow colored spots appear on the upper surface of leaves which spread upto the veins. It gets restricted at the veins. This gives the leaf a mosaic appearance.
- Owing to the presence of moisture, the corresponding lower surface of the affected leaves have a purplish growth.
- The leaves turn necrotic, yellow and ultimately fall off.
The pathogens primarily spread through soil and weeds. They also spread through rain water splashes.
- While transplanting watermelons ensure that the plants are free of the disease.
- Apply fungicide before and after installing the row cover if any.
- There must be enough air circulation in the crop and the humidity level must be kept in check.
- Excess irrigation must be avoided- drip irrigation would ensure just enough water in the soil.
- The field must be constantly monitored.
Nature of Damage
The pathogen mainly affects the upper foliage and growing younger parts. The diseased plants defoliate prematurely and die. In case fruits mature, they are deformed.
- Powdery, whitish, superficial growth on the growing parts, stems and foliage. The growth covers the entire area superficially.
- Diseased areas turn brown and dry.
- Fruits remain underdeveloped.
The fungus is found in dormant buds and parts of plants. It spreads through the infected plant debris and also through conidia by means of wind.
- Ensure proper air circulation
- Aerate the soil before sowing
- Monitor the leaves constantly for appearance of superficial powdery white growth.
- Apply fungicide regularly.
Nature of Damage
The fungus needs an optimum temperature of 30⁰C with high levels of humidity for 24 hours. It produces a thin film of water on the leaves.
- Begins with a thin film of water on the leaves
- The lesions gradually turn into yellow, dark brown and black irregular spots.
- Stem lesion girdle the stem.
- Vines wilt away.
- Fruits produce circular, sunken cankers that maybe about 6mm deep. This is the most diagnostic symptom of the disease.
- The center of the lesion which is the black in color is covered with a mass of spores (salmon colored) that is gelatinous in nature. This happens in presence of moisture.
The fungus typically spreads from the debris residue of previous crop.
It is hard to control the disease. One way to deal with it is to treat the affected plants with neem oil and crop rotation.
Alternaria Leaf Spot
Nature of Damage
Caused by fungus the disease is favored when the weather is wet for a long period of time.
- Spots first appear on the topmost portion of the plant.
- The older leaves have broad spots on them that vary in shape from round to irregular.
The fungus mainly spread through soil and plant debris. However, it can also spread through rain.
Crop rotation and burning the debris after harvests are some of the ways to manage the disease. If detected during cultivation, then spraying chemicals like mancozeb (0.2%) or copper hydroxide would help keep the disease in check.
Nature of Damage
- Chlorosis of leaves is the first symptom of the disease.
- Leaves wilt from bottom to top progressively.
- The infected stem exhibit a brown discoloration
It spreads through soil in the form of chlamydospores.
Seeds and plants ready for transplantation must be free of infection. The soil must be fumigated before sowing. Using resistant varieties of the seeds would help deal with infection.
Watermelon Bud Necrosis Virus
Nature of Damage
Caused by viruses, thrips play host to the virus. The population of thrips increases during the hot and dry climate.
- Leaves develop chlorotic rings and mottling
- Plants are stunted in growth
- The ring spots turn brownish black and leaves become brown and distorted.
- Fruit surface have ring spots ta tan, become necrotic and develop lesions.
Thrips population increase rapidly when the climate is hot and dry thus aiding the spread of disease.
One of the best ways to check the spread of diseases is to check the plants, leaves, soil, weather etc. on weekly basis. Action must be taken when needed such as removing the infected plants, collecting the egg masses, etc.
Watermelons don’t sweeten after they are picked, so harvest time is important. They generally ripen over two weeks so keep your eye on them.
how to tell if watermelons are ripe:
- Thump it. If the watermelon sounds hollow, it’s ripe.
- Look at the color on the top. The watermelon is ripe when there is little contrast between the stripes.
- Look at the color on the bottom. A green watermelon will have a white bottom; a ripe melon will have a cream- or yellow-colored bottom.
- Press on it. If the watermelon sounds like it gives a little, it’s ripe. (Rhodes doesn’t like this method because it can ruin the quality of the fruit.)
- Check the tendril. If it’s green, wait. If it’s half-dead, the watermelon is nearly ripe or ripe. If the tendril is fully dead, it’s ripe or overripe; it’s not going to get any riper, so you might as well pick!
- Stems should be cut with a sharp knife close to the fruit.
- Watermelons can be stored uncut for about 10 days. If cut, they can last in the refrigerator for about 4 days. Wrap tightly in plastic.