Leaf Spot

Leaf spot diseases produce defined areas of dead or discolored tissue on leaves. They are among the most common tree diseases and are caused by a wide variety of fungal and bacterial pathogens. Spots may be circular, angular, or irregular in shape, and they often feature distinct colors, borders, or concentric ring patterns that aid in diagnosis.

Common leaf spot diseases include anthracnose on sycamore, oak, and maple; Septoria leaf spot on various species; tar spot on maple; and shot hole disease on cherry and plum. Most leaf spot pathogens overwinter on fallen infected leaves and release spores during spring rains, initiating new infections on emerging foliage. Cool, wet spring weather typically favors leaf spot epidemics.

While leaf spots are unsightly, most are cosmetically damaging rather than life-threatening to established trees. A single season of moderate leaf spot rarely requires treatment. However, severe or repeated defoliation from leaf spot diseases can weaken trees over time. Cultural management includes raking and removing infected fallen leaves to reduce overwintering inoculum, improving air circulation through selective pruning, and avoiding overhead irrigation. Fungicide applications may be warranted for recurring severe infections on high-value trees.