Apple and Pear Disease - Gray Mold

The disease develops very quickly at cold storage temperatures. Also known as nest rot or cluster rot, gray mold can cause large losses because of its ability to spread from infected to adjacent healthy fruit in storage.

Symptoms

Gray mold lesions first appear as pale tan areas without sharp margins. Infections may originate from wounds, stem punctures, or the stem or calyx end of the fruit. As the decay enlarges, the older portions of the decay may turn darker brown, but the edges often remain a paler color. On red apples, dark areas may persist around lenticels even after the fruit are completely decayed, and these give the fruit a speckled appearance. On firm green pears, the decay is often water-soaked and gray-green, but it is brown on riper fruit and at higher temperatures. On less mature apples and pears, the rotted tissue is firm and does not separate easily from healthy tissue, but the rot is softer on riper fruit. In advanced stages, the decayed flesh has a sweet, cider-like odor. Under high humidity, white or gray-white mycelium may develop on the surface of decayed areas. Little sporulation occurs at cold storage temperatures.

Disease cycle

Gray mold lesions first appear as pale tan areas without sharp margins. Infections may originate from wounds, stem punctures, or the stem or calyx end of the fruit. As the decay enlarges, the older portions of the decay may turn darker brown, but the edges often remain a paler color. On red apples, dark areas may persist around lenticels even after the fruit are completely decayed, and these give the fruit a speckled appearance. On firm green pears, the decay is often water soaked and gray green, but it is brown on riper fruit and at higher temperatures. On less mature apples and pears, the rotted tissue is firm and does not separate easily from healthy tissue, but the rot is softer on riper fruit. In advanced stages, the decayed flesh has a sweet, cedarlike odor. Under high relative humidity, grayish spore masses and/or fluffy white or gray-white mycelium may develop on the surface of decayed areas. Occasionally infections can produce sclerotia (hard, black fruit bodies) on the surface of the infected fruit.

Management

Bin sanitation is an important measure for control of gray mold in order to minimize spores brought in from the field. Postharvest fungicides are also effective for controlling gray mold; however, fungicide resistance is an issue and rotating chemicals with different FRAC groups is recommended.