My oak tree leaves have brown spots and are falling off. What’s wrong?
With all the rain and cloudy, cool, humid weather this year, many gardeners have oak tree leaves with brown splotches of dead areas. We could see that the brown splotches were actually preceded by light green blisters, and the affected leaves were malformed and twisted.
This damage is caused by oak leaf blister, a fungus that attacks the leaves of certain oak species as they are emerging in early spring. The spores of this fungus overwinter on the tree, but only become infectious if conditions are right for their development.
Cool, wet weather favors this pathogen, and we definitely had that this year, much more so than any spring in recent memory, which is likely why our outbreak seems to be especially prevalent this year.
This fungus only affects the first flush of growth in the spring, so leaves that develop later in the season won’t be affected at all.
In severe infestations, the tree may drop all of its leaves, but that usually doesn’t happen. And the infection doesn’t progress past the leaf tissue, so there’s no long-term damage to worry about. Just let the issue run its course. Oak trees will grow new leaves and recover quite quickly.