During wet seasons, oak leaves can turn brown prematurely due to fungal leaf diseases such as anthracnose and Actinopelte leaf spot. However, many oaks, especially pin oak and red oak, are infected with bacterial leaf scorch, caused by Xylella fastidiosa. Leaves of infected branches are green in springtime, but in late summer become brown around the leaf edges or at the tips, while the part of the leaf nearest the mid-vein or the base remains green. Scorched leaves fall from the tree prematurely, but the tree again leafs out normally in the spring.
After several years, all the branches of the tree are infected and small twigs and branches fail to leaf out and die. Eventually (10 -15 years), the die back becomes so pronounced the tree must be removed.
There is no practical cure for bacterial leaf scorch disease. Towns and neighborhoods should replace lost trees, and emphasize planting diverse species along streets and roads and in home and public landscapes.
You may want to read the following publication from the United States National Arboretum: BACTERIAL LEAF SCORCH OF SHADE TREES.
