Therefore, the disease can occur on fruit on the tree, in the packinghouse, in transit, in storage and in the marketplace. A white mold is first seen growing on the peel. The mold later turns green because of the large number of green spores produced. Decayed fruit becomes soft and shrinks. 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.