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.