Because oak trees are slow-growing, any disease that can shorten its life span should be taken seriously. Many oak tree conditions will first become apparent in the tree's leaves. By diagnosing tree leaf symptoms, you can determine the proper treatment for oak tree problems.
Determine which variety of oak you have. Diseases such as oak anthracnose affect mainly oaks within a white oak family, while bacterial scorch affect red and black oak trees. Knowing your tree variety will help you to narrow down your troubles to a specific range.
Note the time of year that the damage occurs. Many insects and diseases are most common in certain times of the year. Infestations of oak leaf blister that cause leaves to curl occur mainly in spring, while powdery mildew is active in fall and spring and bacterial scorch occurs during summer months.
Compare leaves from various parts of the tree to determine where the damage occurs. Some diseases strike new growth first. Powdery mildew will cause leaves on the interior canopy to curl and distort, but will not affect exterior leaves.
Note the characteristics of your leaves. Although there are many diseases and pests that can cause oak leaves to curl and turn brown, each one has specific characteristics. Galls are a pest problem that causes brown lumps on your leaves. Although oak leaf blister also causes raised bumps on leaves, the bumps are not brown. But they do cause leaves to curl once they merge into larger blisters. Oak anthracnose causes leaves to become distorted and brown around the edges.
Take cuttings of leaves and place them in a plastic bag. Take these leaves to your county extension service. Agents with the extension service can tell you what diseases and pests are active in your area, and can positively identify your leaf issues.