Blue Mold of Apple
Blue mold, a common rot of stored apples and pears, is caused by the fungus Penicillium expansum. Other names for the disease are "soft rot" and "Penicillium rot." Soft rot is a disease of ripe fruit and develops mostly on apples that are picked before they are mature. Firm fruit in the same container as decaying fruit might absorb a moldy odor and flavor.
Soft rot appears as soft, light-brown, watery spots that begin around injuries or lenticels on the outer surface of fruit. Rotted fruits have a characteristically moldy odor and flavor. When the relative humidity is high, grayish-blue masses of spores might appear on the fruit surface. Under favorable conditions, the entire fruit can rot in 2 weeks.
Spores of the soft rot fungus are present almost everywhere and can survive long periods of unfavorable conditions. Injuries to fruit, especially during picking and handling operations, are the primary points of entry. At ordinary temperatures, infected fruit can rot in 2 weeks or less.
To control blue mold, it is important to prevent fruit from becoming bruised during picking and handling. Fruit should be harvested at optimum maturity. It is also essential to move harvested fruit into cold storage as rapidly as possible.