WSU Tree Fruit Research & Extension Center

Tree Fruit Market Diseases

Sunday, March 24, 2019

WSU-TFREC/Postharvest Information Network/Tree Fruit Market Diseases/sootyblotch

Gloeodes pomigena (Schw.) Colby

Occurrence and importance
Sooty blotch is a superficial disease of apple and other pome fruits. It is common throughout the central and eastern apple-growing sections of the United States, but it is rare in the Northwest. The disease occurs in the orchard mainly on late-summer and winter varieties, blemishing the fruits and reducing their market value. Sooty blotch does not develop or spread in transit or in storage and is of minor importance on the market.

Sooty blotch appears as dark granular spots or smudges that may occur anywhere on the fruits (top photo). The spots have irregular shapes and indefinite outlines. They vary greatly in size. The blotches, which are thin fungal crusts, can be removed by scraping or rubbing. Due to moisture loss through the damaged cuticle, the spots become slightly sunken in storage.

Causal factors
The fungus, Gloeodes pomigena, overwinters in infected twigs of many plants. It usually attacks the apples during cool, rainy periods in late spring and summer. Late-summer rains combined with periods of low temperature are conducive to fall infections. Following favorable weather, sooty blotch is often associated with flyspeck, another superficial disease, and this combination may cause serious losses in poorly sprayed orchards.

Control measures
The application of fungicides to protect fruits during the summer will control sooty blotch as well as flyspeck. Recommendations of the State agricultural experiment station or extension service should be followed.

Sooty blotch
Sooty blotch

Sooty blotch, Golden Delicious
Sooty blotch, Golden Delicious

Sooty blotch, Morgenduft
Sooty blotch, Morgenduft

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