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.