Oak Anthracnose

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Oak Anthracnose is a somewhat common but not especially harmful pest of oaks. It infects all oaks but is especially severe on white oak and bur oak. It appears in the spring and summer after a prolonged period of rainy, wet weather.

It first appears as irregular, water-soaked spots on young and wounded leaves of lower and inner branches. The spots soon turn black. When the spots dry out the infected part of the leaf is dead and turns tan or brown. Spots may coalesce into large brown areas. As leaf expansion continues around the dead or infected area, the leaf shape becomes deformed and often cupped.

An infection can cause complete defoliation but that is not fatal. Since the infection occurs early in the growing season, the tree will produce a second flush of leaves.

The fungus overwinters in leaf litter, on twigs and stems, and in cankers.

Oaks

Spring and summer after wet weather

Sources

4, 7, 24, 26, 29, 30, 77.

Forest Insect and Disease Newsletter - Wet Summer 2017. Minnesota Department of Natural Resources

Widespread and common

Oak Anthracnose on northern pin oak