Market Diseases of Apples, Pears, and Quinces
Occurrence and importance
Gray mold rot develops faster at cold-storage temperatures than any other fungus rot of apples. Apples carrying infection in the fall when placed in storage at 31° to 32 °F are often completely decayed by February or March.
Gray mold rots that develop in storage from incipient infections at harvest occur principally at the stem or calyx end. From these initially rotted fruits the rot then spreads to fruits in contact with them to produce "nests" or "pockets" of decaying fruits in the stored package. Hence the disease is often called nest rot or cluster rot.
The Botrytis fungus can also cause a condition known as blossom-end rot of apples in Northeastern orchards.
In Washington a new species was reported as Botrytis mali Ruehle in 1931 from stored apples. This species has not been reported since and appears to cause little loss.
It is believed that the source of gray mold infection is in the orchard. The fungus grows and sporulates abundantly on dead and dying plant material found in orchard cover crops, especially during cool, moist weather. Fruits hanging near the ground are more likely to become infected than those farther from it. As mentioned earlier, fruits infected at the time of storage nearly always decay at the stem or the calyx end. The spores lodge in these cavities and under favorable conditions may develop and attack the stem or calyx parts. From such superficial infection the fungus spreads to the edible part of the fruit. Infected fruits may be completely decayed after 3 or 4 months in cold storage, then they begin to infect fruits touching them.
Apples should be handled carefully, stored and cooled promptly, and maintained at 31° to 32 °F throughout storage.
In the Northwest, most apples are treated with a formulation of sodium orthophenylphenate as a fungicidal wash at packing time. This should aid in controlling gray mold rot. (See Pears, Gray Mold Rot).