Storage

Watermelons are not adapted to long storage. Temperature management is important for optimum watermelon quality.

Watermelons store satisfactory at 15°C for up to 2 weeks. For long-term storage, the fruits should be kept at about 12°C and 85% RH.

At temperatures below 50°F, chilling injury can develop, causing decreased redness and juice leakage of the internal flesh, and surface pitting and Alternaria decay to the melon rind. Chilling will also cause discoloration in the internal flesh after the melon is warmed to room temperature if it was bruised before cold storage.

Holding watermelons for up to a week at room temperature can improve flavor and color. However, after several weeks at room temperature, they have very poor flavor and texture.

Handling

Watermelon fruits are rather fragile and susceptible to breakage and bruising and should be handled and shipped with care. In Africa, fruits are often greatly damaged as a result of poor handling and transportation.

Ensure that the employees handle the watermelons in a manner that will not cause damage to the fruit. Do not allow the melons to be tossed up onto the truck, nor allow workers to stand on the crop while sorting and loading.

Trucks, wagons, and crates should be padded and watermelons should be arranged to limit movement to protect from interior bruising. Pack the watermelons in layers no more than four deep. The tops of the containers should be covered to prevent sunburn in transit.

Melons should not be shipped in closed trucks or stored with fruits (bananas, peaches) and vegetables (tomatoes, cantaloupe) that emit ethylene. Ethylene is a colorless gas regarded as the natural aging or ripening hormone. When exposed to ethylene, watermelons break down internally, and the flesh takes on a water-soaked appearance. This leads to flesh softening and flavor loss.

Yield

The yield of watermelon varies according to the system of cultivation, variety, season and several other factors. The average fruit yield varies from 20 to 25 t/ha.

The sweet flavor of watermelons

Sugar content does not increase after harvest; however, red color will continue to develop after a slightly immature melon is picked.

There are differences in sugar content from one variety of watermelon to another. Poor flavor and lack of sweetness due to poor fertility, low potassium, magnesium or boron; cool temperatures; wet weather; poorly adapted variety; loss of leaves from disease or picking melons unripe.

Harvesting

Watermelons reach harvest maturity five to six weeks after pollination, depending upon variety and season. The harvest may continue for a further 40-50 days.

Make sure you know the approximate number of days to maturity for your variety.
Watermelons should be harvested before vines become withered, in which case the fruit is over mature.

Over maturity is characterized by flesh mealy in texture and reddish-orange in color.

Determining optimum maturity of a watermelon can be difficult. There are several clues to look for when harvesting:

1. A change in the color of the ground spot (where it lies on the soil) from white to light yellow.

2. A change of tendrils nearest the fruit from green to brown and dry.

3. A change in sound when thumped from a metallic ringing sound to a soft hollow sound.

4. A breakup of green bands at the blossom end of the fruit.

5. Development of ribbed indentations that can be felt with fingertips.

6. The skin becomes resistant to penetration by the thumbnail and is rough to the touch.

No single indicator is absolute for determining ripeness, because maturity differs with variety, location and plant growth.

If harvested immature, red color will develop, but the flesh will never develop acceptable sweetness, because sugar content does not increase after harvest.
Watermelons should be cut from the vine rather than pulled, twisted or broken off. Pulling stems out provides an entrance for bacteria and fungi that can cause souring and can decay the internal flesh.

A sharp knife is used to cut the fruit from the vine, leaving about 3 cm of peduncle attached to the fruit This helps to reduce rotting or deterioration at the stem attachment during storage.

Do not place melons with bottom sides turned up, as the ground spot is easily sun scalded.

Never store picked melons in the sun.

Harvest early in the morning when field heat is low and the fruits are most turgid.

Watermelons should be consumed within two to three weeks after harvest, primarily because of loss of crispness.

Pest and disease

Insect: Thrips, aphids, cucurbit beetle, melon fruit fly, spider mites, and cutworm. Spray insecticide at manufacturer recommendation.

Disease: Downy mildew, powdery mildew, mosaic, anthracnose, use appropriate chemicals in controlling these diseases by following the manufacturer recommendation.

Melon Defects:

Blossom-end rot (BER):

It is a physiological or no parasitic disorder related to calcium deficiency, moisture stress or both.

Prevention recommendations include adequate amounts of calcium, proper soil pH (6 to 6.5), and a uniform and sufficient supply of moisture.

The incidence of BER usually is quite variable from season to season and tends to occur more readily in oblong melons. Watermelons having BER are considered unmarketable.

Hot, dry winds, nematode damage, excessive fertilizer, low levels of calcium in the soil, pruned roots from late cultivations, and other conditions are contributing factors.

Hollow heart (HH) and white heart (WH):

They are two physiological disorders influenced by genetics, environment and, probably, a number of nutritional factors.

To decrease the incidence of these two problems, only cultivars that have not shown unusually high incidences of HH or WH should be planted.

In addition, the crop should be grown under optimal (as close as possible) nutritional and moisture conditions. HH and WH harm watermelon quality and may be severe enough to cause potential buyers to reject melons.

Sunscald:

Sunscald Caused by sun hitting fruit surface directly. Sunscald occurs most frequently in varieties that have dark green rinds.

Developing and maintaining adequate canopy cover to afford protection (shade) to the melons may prevent sunscald. Do not allow harvested melons to lay by roadside for long periods before pickup.

Sunscald reduces quality by making melons less attractive and may predispose the melon to rot.

Stem splitting:

Stem splitting can occur in seedlings grown for transplanting. This problem seems to be associated with high humidity and moisture that can occur under greenhouse conditions.

Watering evenly to maintain soil moisture, avoiding wet-dry cycles in the media and good air circulation may help alleviate these problems.

Sandblasting:

Sandblasting occurs when wind and blowing sand damage seedlings when first planted.

This appears as dead or dying tissue usually on the side of the prevailing winds.

Transplant handling damage:

Transplant handling damage may result at the soil line because of handling. Tops will flop around and may wilt more readily. In addition, brown or callused tissue may appear at the soil line.

Transplants with this damage should be planted slightly deeper to prevent any further damage.

Misshapen melons:

Misshapen melons (gourd-necked or bottlenecked) are commonly produced by varieties with long fruits.

Misshapen melons caused by poor pollination during wet, cool weather and lack of bee pollinators.

Occasionally melons of any variety may be misshapen because they lie on uneven ground or were injured while small.

Bursting:

Bursting may result from an uneven growth rate, which is particularly associated with heavy rainfall or irrigation when fruits are maturing.
The percentage of bursted fruits is usually low, and types with round fruit are more susceptible.

Rind necrosis:

Rind necrosis is an internal disorder of the watermelon rind.

Symptoms are brown, corky or mealy textured spots in the rind that may enlarge to form large bands of discoloration 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.

Pollination

A poor fruit set in watermelons is usually a result of poor pollination. Watermelons bear separate male and female flowers on the same plant (monoecious).

When flowering begins in watermelon, male flowers will be produced at every node while female flowers will be produced approximately every seventh node.
Pollen must be transferred from flower to flower by pollinating insects - primarily honey bees. For proper pollination, a female flower should receive eight or more bee visits. Insufficient pollination results in misshapen melons.

Flowers open one to two hours after sunrise. Female flowers are receptive to pollen throughout the day although most pollination takes place before noon. In the afternoon the flowers close, never to reopen, whether pollinated or not.

Watermelon flowers are not nutritionally attractive to honeybees; therefore, blooming weeds or other crops can out compete watermelons in attracting honeybees. Destroy nearby flowering plants that may be attractive to honeybees. This will ensure that the bees work the watermelon flowers exclusively.

Since numerous visits are required to each flower during a relatively short period, it is necessary that sufficient numbers of bees be available near the field. It is recommended that at least one honey bee colony be introduced for every acre during the blooming period since native bee populations may not be adequate, or may not coincide properly with the blooming period.

Common causes of poor fruit set include lack of bees for pollinating or cool, wet weather that slows bee activity during bloom.

Bees require water for survival and their efficiency may be improved by a water source near the hives. Some shade may also be beneficial.

When flowers are developed on the plants, do not use insecticides, which are extremely toxic to bees, and apply them at dusk after the bees have bedded for the night.

Q. Do watermelons readily cross with other vine crops resulting in off-flavor and poor quality fruit?

Watermelon varieties readily cross with each other and with the wild watermelon. Watermelons will not cross with cantaloupes, cucumbers, pumpkins or squash. Off-flavor or odd-shaped fruit is generally caused by growing conditions and not cross-pollination.

Pruning

Watermelon plants need to be pruned of excess fruit to allow the correct number of fruit to properly develop and obtain marketable size.

Pruning is performed to achieve a balance between vine growth and fruit set. Pruning increases average fruit weight while reducing the number of unmarketable (cull) fruit.

Pruning should occur in two stages:

The first pruning removes all of the unmarketable fruit (Remove misshapen and blossom-end rot fruit).

While the second removes the late set fruit in order to increase the size of the remaining melons.

There should only be two fruits per vines of varieties, which produced large size fruits and 4-6 in the case of small-fruited varieties after pruning.

To avoid disease spread, do not prune melons when vines are wet.

Fruit in contact with soil may develop rotten spots or be damaged by insects on the bottom. Place a board or several inches of light mulching material, such as sawdust or straw, beneath each fruit when it is full-sized.

Turning

Turning:

Watermelon vines need to be ‘turned’ or adjusted along the rows 25 days after planting to facilitate watering and weeding but main vines should not be touch anymore.

Weed Control

Watermelons, as with most crops, require early season weed control to ensure a quality crop. Watermelons should be kept free from weeds by shallow hoeing and cultivating.

Weed control is essential for good yield and it makes harvesting easier. In addition, the spreading nature of this crop makes weed control difficult once the vines begin to form.

Shallow cultivation by off baring, 15 days after planting followed by hilling up at 30 days after planting and hand weeding thereafter until the crop have attained sufficient size to cover the soil which in turn will suppress the growth of weeds.

Most of the pre- and post emergence herbicides are phytotoxic to the seedlings or reduce plant growth. When this herbicide is used for control, it should be applied to weeds 3 days before watermelon seeding.

Irrigation

Watermelons, with their long vines and large leaves, have high rates of water loss via transpiration. Consequently, they benefit from supplementary irrigation, especially when grown on light, sandy soils.

Heavy soils that have been soaked just before planting may contain sufficient moisture for average crops of watermelon without the need for additional irrigation. Watermelon has deep roots and can survive relatively dry conditions.

Melons are drought tolerant. The plants are deep rooted. Growers with limited irrigation capabilities can often increase yields with only one or two irrigations. However, they require uniform irrigation for optimum growth and yield

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Critical periods, when moisture stress is most harmful, are:

• 
  Before seedling emergence: Inadequate moisture at planting results in poor and uneven emergence.
• 
  At early bloom: Moisture shortage at bloom results in poor fruit set and misshapen fruit.
• 
  The last ten days before harvest: Moisture stress close to harvest greatly reduces melon size and results in rapid vine decline.

Excessive irrigation after the melons have been water stressed may result in fruit splitting.

Avoid irrigating in the late afternoon or at night to reduce foliage diseases. Do not allow the fruits to get wet while irrigating.

Reduce irrigations as fruit reach harvest stage. Watering during the ripening season may delay harvest, cause splitting and reduce sweetness. Two weeks prior to maturity irrigation should be stop.

Soil type does not affect the amount of total water needed, but does dictate frequency of water application. Lighter soils need more frequent water applications, but less water applied per application.

Watermelons respond very favorably to drip irrigation. Applying water regularly, will increase fruit set, fruit size, and yield.

Fertilization

Watermelon responds well to fertilizers, especially to organic matter. The amount required depends on the nutrient status of the soil. In general application at a rate of 20–30 t/ha organic manure, 50–60 kg N, 10–15 kg P and 20–30 kg K per ha is suitable for good performance.

A soil test is recommended for each field to be planted. The fertilizer doses to be applied depend on variety, fertility of soil, climate and season of planting. Changes in bed spacing often lead to needed changes in fertilizer amounts.

Generally well decomposed FYM (15-20 t/ha) is mixed with the soil during plough.

The recommended dose of fertilizer to be applied per hectare is 100 kg N, 50 kg P2 O5 and 50 kg K2 O.

Watermelons are a relatively long-season crop; therefore, applying fertilizer in small amounts several times throughout the season will maximize production.

Current recommendations include applying All required phosphorus (and should remain available throughout the growing season because it is relatively immobile in the soil.) plus one third of the N and K before planting and following this with two more applications at 3 and 6 weeks of the remaining N and K.

It is better to complete all the fertilizer applications just before the fruit set.

Planting

Direct seeding is the most common method of planting. In cooler climates, it may be necessary to start the seedlings in a greenhouse to ensure good germination.

Seed rates per ha are 1–2 kg for direct-seeded and 0.3–0.5 kg for transplanted watermelon.

Plant spacing requirements vary depending on variety selection, growing area, time of planting, and soil type, but should be around 60-90 cm and approximately 2 meters between rows.

A. Direct seeding:

Watermelon seed should not be planted until soil temperatures are warm enough to ensure rapid germination. Plant after the soil is warm and when all danger of frost is past.

Triploid plant population density should be 10 to 20% less than that recommended for production of standard watermelon varieties.

Per hill, 3–4 seeds are sown at a depth of 3–4 cm; 3–4 weeks after sowing, at the 2–4 leaf stage, seedlings are thinned to 1–2 per hill (Thinning is practiced 15 to 25 days after sowing). The plants should be thinned to one plant per hill (two if selection is not good).

Seed will remain viable for at least 8 years when stored dry at temperatures below 18°C.

There is no seed dormancy in cultivated seed- and watermelons, but germination is retarded under high temperature regimes.

Germination can be accelerated by pre-soaking in water for 24 hours after scarifying the seed at one end, especially for cultivars that have a hard seed coat. When planted in warm soil, seedlings will emerge in a week or less.

Use fungicide-treated seed. Watermelons are subject to damping off and decay in cool wet soils.

B. Transplanting:

Transplanting watermelons offers several advantages:

1- Plants can be produced under greenhouse conditions when outdoor conditions are not conducive to plant growth.

2- Seed-use efficiency increases, which is especially important with costly hybrid and triploid seed.

3- Soil crusting and damping off, detrimental to seedling growth, can be eliminated or reduced.

4- Planting depth is uniform.

5- It usually results in earlier harvests.

6- It is the only cost-effective way to grow seedless watermelons.

Watermelons suffer transplant shock if the roots are even minimally disturbed. So seedlings must be grown in containers such as peat pots, Speedling trays, or Jiffy pots to be successfully transplanted.

Sow seeds in small plastic pots or containers using a potting mix that has good water-holding capacity and good drainage such as peat moss, commercial potting soil, or a potting mix prepared from soil, compost, rice hull, and vermiculite or sand.

Sow one to two seeds per container for open-pollinated varieties and one seed per container for hybrids to reduce seed costs. Pinch off or cut seedlings to avoid disturbing the roots. Do not pull seedlings out of the container to thin.

1- Watering:

Uniformly moist media will ensure good germination, but overly wet media will encourage damping off and high seedling mortality.

Established transplants should be watered only when necessary. Excessive watering leads to succulent plants with restricted root growth. Water should be applied only when the surface of the media is dry to the touch.

As plants grow larger, their water needs will increase. They may need water daily when approaching transplant size. The media should be moistened thoroughly until water drips through the container’s drain holes.

Water the seedlings in the morning, to allow the foliage to dry before night. Wet foliage encourages disease.

2- Fertilizing:

Plants are fertilized every three days with a solution containing 50 ppm N from Ca(NO3)2 and KNO3 from cotyledon expansion until the first true leaf is fully expanded, then with a 200 ppm N solution applied every other day until the second true leaf is fully expanded, finally the fertilizer is reduced for several days before transplanting to the field.

3- Hardening-off:

Watermelons need not undergo a long hardening-off period; three to four days are sufficient.

Hardening-off can be initiated by reducing greenhouse temperature and by withholding water or limiting fertilizer. Hardened plants are more able to withstand chilling stress, mild water stress, drying winds or high temperatures. Hardened plants generally produce new roots more rapidly than unhardened plants.

4- Planting:

Plants generally will take three to five weeks to be field ready depending on variety and growing conditions. Plants grown under less than ideal conditions will take longer to produce.

Seedlings are ready for transplanting when they have 2 or fewer true leaves at the time of transplanting. Older plants establish very slowly in the field.
Bare-root plants will not survive so pull seedlings with their root balls intact before transplanting.

Transplant seedlings into the field at spacing similar to those used for the direct seeding method.

Transplants should be watered as soon as possible after transplanting to remove air pockets surrounding the roots and to ensure sufficient soil moisture for good root establishment.

If you grow seedless melons, you must also plant a row of a standard seeded variety for every three rows of the seedless melons. The seedless melon varieties do not have the fertile pollen necessary to pollinate and set the fruit.
Use a starter fertilizer solution when transplanting. Use a water-soluble fertilizer such as 10-34-0. Mix 1 quart of this material in 50 gallons of water.

Preparing the field

About one month before planting the watermelons, the field should be prepared thoroughly by plowing and harrowing and removing the different plant debris. It should also be pulverized and leveled, furrows are made 2 meters apart.

Land preparation involves one or more tillage operations performed:

(1) To make the soil more suitable for seeding and seedling (or transplant) establishment,

(2) To enhance productivity by providing the best soil structure for subsequent root growth and development,

(3) To help control some disease problems.

Before planting, the ploughed field can be treated with herbicide to kill germinating weeds, particularly perennial grasses. After the weeds have died, the soil may be fertilized with organic material or inorganic preparations.

Adding OM improves soil structure, which, in turn:

Helps to reduce compaction and crusting.

Increases water infiltration and decreases both water and wind erosion.

Also of importance, OM serves as a storehouse of many plant nutrients.

Furthermore, OM improves the efficiency of applied fertilizers by increasing the soil’s ability to retain plant nutrients under leaching conditions.

Choosing a variety:

There are hundreds of cultivars available for production and contain much diversity.

Watermelons range in shape from round to oblong. Rind colors can be light to dark green with or without stripes. Flesh colors can be dark red, red or yellow.

Selection of a cultivar for production should be based on the optimal yield and profit that can be obtained. Also, the market availability of seed or transplants, and cultural conditions of the site should be taken into consideration.

Selecting varieties acceptable for your market is important. 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 and amount of accumulated sugars, be adapted to the production area (drought tolerance), and have the highest level of needed insect and disease resistance available.

Watermelon varieties fall into three broad classes based on how the seed was developed:

Open-pollinated:

Open-pollinated varieties are developed through several generations of selection.
The selection can be based upon yield, quality characteristics and disease resistance.

Open-pollinated varieties have true-to-type seed (seed saved from one generation to the next will maintain the same characteristics) and are less expensive then F1 hybrid varieties.

F1 hybrid:
Hybrid crosses are beginning to take rise to the watermelon industry.

F1 hybrids are developed from two inbred lines that have been selfed for several generations and then crossed, with the subsequent seed sold to growers.

F1 hybrid seed will exhibit increased uniformity of type and time of harvest compared with open-pollinated seed and can exhibit as much as a 20 percent to 40 percent increase in yields over open-pollinated varieties grown under similar conditions.

The disadvantages of F1 hybrid seed are cost and availability. F1 hybrid seed will be as much as five to 10 times as costly as open-pollinated seed, and available F1 hybrid varieties will change from year to year.

Triploid (seedless):

These are developed by creating watermelon plants with double the usual chromosome number (tetraploid male plant ) and crossing them with normal watermelon plants (diploid female plant).

The seeds from this cross-breeding will germinate and grow into a plant that have one-and-a-half times the normal chromosome number. Consequently, they can bears flowers, but the flowers will not produce viable sperm-bearing pollen or eggs because of the odd number of chromosome sets. Because of this, seeds are not usually formed.

Triploid seeds will be even more expensive than F1 hybrid seeds, and the melons should command a premium in the marketplace.

Although triploid watermelons are referred to as seedless, they are not truly seedless but rather have undeveloped seeds that are soft and edible.

Growth-promoting hormones produced by the developing seed enhance fruit enlargement in seeded watermelons. Because triploid melons do not contain developing seed, they require pollen to stimulate fruit growth. This creates a problem because triploid plants are essentially sterile and produce little, if any, pollen. The solution is to interplant rows of seeded pollenizer melons with rows of triploid watermelons.

Keep in mind that melons from the pollenizer variety must be easily separated from the triploid melons at harvest. The normal cultivar chosen usually has a different rind color or pattern from the seedless variety.

Make sure the seeded melons are also acceptable to your buyers because about one-third of all the melons produced will be from the seeded pollenizer.

Because seedless types do not put energy into seed production, the flesh is often sweeter than normal types and the vines are noticeably more vigorous as the season progresses.

Watermelons are also grouped according to fruit size and shape (Watermelons range in shape from round to oblong), color of rind (Rind colors can be light to dark green with or without stripes), flesh (Flesh colors can be dark red, red or yellow), and seeds (can range in color from black to white).

Climate and soil requirements

Climate:
The crop prefers a hot, dry climate with mean daily temperatures of 22 to 30°C. The crop is very sensitive to frost.

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.
Melon seed do not germinate well in cold soil.

Fruits grown under hot, dry conditions have a high sugar content of 11 percent in comparison to 8 percent under cool, humid conditions.

The length of the total growing period ranges from 80 to 110 days; depending on variety and climate (Temperatures above 35°C or below 18°C will slow the growth and maturation of the crop).

Soil:

Watermelons grow best on soils that hold water well and have good air and water infiltration rates. Soil should have a pH of 6 to 7. Apply lime if soil pH is too low.

It is more tolerant than muskmelon to medium salt concentration with EC(e) values (EC(e)x1000) ranging from 10 to 4.

Fine sands produce the highest quality melons when adequate fertilizer and water are provided. Cultivation in heavy textured soils results in a slower crop development and cracked fruits.

To show a profit, a grower must produce good yields of high-quality melons. High yields of quality melons can be obtained only with careful management.

Nutritional value and health benefits:

Watermelons are low in calories and very nutritious.

Watermelon is high in lycopene, second only to tomatoes. Recent research suggests that lycopene, a powerful antioxidant, is effective in preventing some forms of cancer and cardiovascular disease.

Watermelon is also high in Vitamin C and Vitamin A.

Potassium is also available, which is believed to help control blood pressure and possibly prevent strokes.

Introduction:

Watermelon Citrullus lanatus (Thumb.) is native to the dry areas in tropical and sub-tropical Africa south of the equator.

Although watermelon is native to central Africa, it was first grown by ancient Egyptians (Egyptians grew watermelons more than 5,000 years ago).

The uses for the watermelon at this time included a source for water (watermelons are comprised of 90% water), staple food, animal feed, and fermentation for alcohol production.

The crop can survive the desert climate when groundwater is available.