Some common diseases affecting oak trees include anthracnose, oak branch die-back, leaf blister and twig blight. Most of these diseases can be controlled if they are identified in their early stages and the appropriate steps are taken to protect the tree from further damage.
Anthracnose is a fungal disease that first afflicts the foliage of the oak tree, appearing as black spots with a tar-like appearance. The fungus curls and distorts the leaves. If untreated, it causes die-back and girdling. Branches infected by anthracnose should be removed from the tree, and a dose of fertilizer should be applied in the spring to strengthen the tree.
Oak branch die-back results in wilted leaves, die-back of the tree's branches, and peeling bark. Pruning the tree can control the spread of the disease.
Leaf blister causes infected leaves to curl, gall and drop from the tree. It occurs when the leaves are wet. Pruning can prevent the spread of leaf blister and improve the appearance of the tree, while watering only when adequate rainfall is unavailable can prevent it.
Twig blight also affects the appearance of the leaves, causing them to discolor and creating unattractive foliage that remains on the tree. Over-watering is a common cause of twig blight.