Infection by the cherry leaf spot fungus causes small purple leaf spots (up to 3mm) that eventually turn brown. These spots sometimes drop out, causing a shot hole appearance. Affected leaves turn bright yellow and drop prematurely.
The causal fungus, Blumeriella jaapii (once known as Coccomyces hiemalis) may infect sour cherry, sweet cherry, chokecherry, common plum, wild plum, and other Prunus species.
Leaf spots usually first appear when the leaves reach full size. Spot may coalesce together and cause large areas of leaves to turn brown. Mild wet weather promotes cherry leaf spot.
The fungus that causes the disease survives the winter on infected leaves that fall to the ground. Spores that are released from these leaves during rainy periods in the spring may infect newly emerging leaves. Raking and removing fallen leaves helps to break the disease cycle. Fungicides can be used to protect leaves from infection. The first spray should be applied at petal fall and continued at two-week intervals through harvest.
This article originally appeared in the July 30, 1999 issue, p. 106.