WSU Tree Fruit Research & Extension Center

Tree Fruit Market Diseases

Sunday, March 24, 2019

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

Mycosphaerella pomi (Pass.) Lindau.

Occurrence and importance
Fruit spot (Brooks' spot) is most common in apple orchards of the Northeast, but it appears occasionally in areas east of the Great Plains. It is generally considered a minor disease that occurs erratically, but it may cause severe losses at times. Varieties most seriously affected are Baldwin, Jonathan, Rome Beauty, Delicious, Grimes Golden, and Stayman.

The disease appears on the fruits in midsummer as scattered, small, highly colored spots, usually more abundant around the calyx end (see photo). The spots are 1/8 to 1/4 inch in diameter and deep red or black on the red areas and dark green on green or yellow areas. The roughly circular to irregular spots darken sink slightly, and become flecked with black in their centers late in the season or after the apples are in storage. The flecks in the flesh are best observed by making the thinnest possible paring of the surface of the spots.

The speckled appearance readily distinguishes fruit spot from all other spot diseases of apples. Fruit spot is further distinguished from bitter pit by not being markedly sunken except in the later stages, by the absence of brown, spongy tissue below the surface spot, and by having no connection with the vascular tissues.

Causal factors
Fruit spot is caused by the fungus, Mycosphaerella pomi. Starting in early summer, fruits are infected during wet periods by spores arising from fallen leaves of the previous year. Infections overlooked at packing time will develop extensively if fruits are not cooled quickly. There is very little disease development once the fruits have been placed in cold storage.

Control measures
The disease can be controlled by spraying with many of the organic fungicides now available. The recommendations of the State agricultural experiment station or extension service should be followed.

Fruit spot (Brooks' spot)
Fruit spot (Brooks' spot)

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