Blue mold is a fungus that commonly affects fruits that are put into cold storage; the mold develops quite slowly at these cold temperatures. When it is brought to room temperature, green mold (which does not grow well in cold temperatures) predominates most infections where both molds are present.
Blue mold is actually Penicillium italicum and is not as serious as the green mold that occurs in Florida. The spores become airborne and grow large colonies on the surface of fruit that have become infected.
They will go on to contaminated the equipment, water in any tank the fruit comes into contact with, the packinghouse, transit containers, any storage room, and eventually the retail market area if the infected fruit is allowed to travel that far.
The fungus survives outside of the fruit packing industry in soil debris and since the spores are airborne, they can infect fruit on the tree or on the ground whose skin is damaged.
Any infected fruit that is boxed with healthy fruit will cause the whole carton to become infected and care should be taken to remove any diseased fruit from the lot as soon as possible. Before it makes it to the retail market, any diseased fruit must be removed.
The cycle of producing spores and infecting fruit can be repeated a great number of times in storage rooms and fruit packing houses and since this is true, it will eventually develop a strain that has a resistance to any chemical fungicides.
The symptoms of blue mold appear similar to sour rot or green mold; a small area of decay begins to form and this manifests as a soft, somewhat watery spot. These lesions will enlarge to about 1 to 2 inches in diameter and white mycelium will form in the center.
Blue spores will begin to form shortly afterward and these are easily turned airborne by either moving the fruit around physically or by a simple air current in the room.
To reduce the incidents of blue mold, both harvesting and handling of the fruit needs to be very careful. High populations of blue mold spores cannot be let to gather in the storage rooms or packinghouses.
Any fruit that is infected should be removed from the area where clean fruit is located immediately and put in a different facility used especially for disposing of it. Equipment should be sanitized on a daily basis.