Oak Leaf Blister
2 (1 = rare 5 = annual)
2 (1 = very little damage 5 = plants killed)
The fungus attacks species in both the red and white oak groups.
The infection site bulges upward on the upper surface and is sunken on the lower leaf surface. The infected area starts out tan and turns brown as the disease progresses.
The fungus overwinters on twigs and bud scales and infects new leaves while they are emerging from the bud when there are mild and moist conditions.
At this time, no chemical control is really necessary in the Midwest since this disease does not cause enough damage to justify a preventive fungicide treatment.