As its name implies, blue mold, caused by the fungus Penicillium italicum , differs from green mold by the bluer color of the powdery mass of spores that develops over the surface of the fruit. Conditions favoring the two diseases are similar. Both fungi grow best at a temperature of 75 o F and their development is slowed by lower temperatures. Cooling citrus fruit during storage and shipping is an effective way to decrease damage. Most citrus fruit can be injured when exposed to low temperatures for extended periods of time even though these temperatures remain well over the freezing point.
Grapefruit is more susceptible than oranges to damage caused by chilling temperatures.
The symptoms are varied, consisting usually of irregular, superficial discoloration of the surface of the fruit and rind pitting. The size of the sunken lesions tends to be smaller and lesions are more numerous as the temperature nears 32 o F. Chilling injury to citrus fruit can be avoided by carefully selecting temperatures for citrus storage or transport. However, because rot and decay increase as the temperature increases, a proper balance must be maintained. Fruit must be picked at proper maturity and handled carefully both in the field and in the packinghouse to avoid chilling injury. Chilling Injury of citrus fruit.