Black Rot on Apple

The black rot fungus, Botryosphaeria obtusa, covers a wide geographical range, attacking the fruit, leaves, and bark of apple trees and other pomaceous plants. The fungus is a vigorous saprophyte and may colonize the dead tissue of many other hosts. However, its parasitic activities are confined mainly to pome fruits.

The disease may occur in three forms: a fruit rot, leaf spot, and limb canker on apple trees, and a fruit rot on pear and quince. In northern regions, losses from black rot result principally from the cankering of large limbs and dieback of twigs and branches. Losses from fruit rot and defoliation resulting from leaf spot can be considerable, especially in warm, humid areas of southern and central fruit-growing regions of the eastern United States.

Symptoms
The first signs of black rot are small, purple spots appearing on the upper surfaces of leaves and enlarging into circles 1/8 to 1/4 inch in diameter. Leaf margins remain purple, while the centers turn brown, tan, or yellowish brown. After a few weeks, secondary enlargement of leaf spots occurs. Because this is not a uniform expansion, the spots become irregular or lobed in shape, at which time they assume a characteristic "frog eye" appearance: a purple margin with a zone of dark brown surrounding the tan-to-gray center. Small, black pycnidia (pimplelike fruiting bodies of the fungus) may appear in the centers.

For more information, please see this Penn State Tree Fruit Production Guide Web page.

Penn State Horticulture Department

For more information on this subject, Please visit the College of Agricultural Sciences Publications Web site.

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