You wait all summer for that brilliant red display from your pin oak (Quercus palustris), but the leaves turn a disappointing brown. Hardy in U.S. Department of Agriculture plant hardiness zones 4 through 8, these trees grow up to 70 feet tall and 60 feet wide. The deeply cut leaves grow up to 5 inches long. Sometimes the leaves naturally turn bronze in the fall, but diseases and other problems can turn the leaves brown. When treating diseased trees, keep pesticides and pruning tools away from children, and do not let children or pets play near treated trees until the pesticide dries. If you are pregnant or nursing, someone else should apply pesticides for you.
Leaf scorch usually shows up in late summer or early fall, after a drought. At first, pin oak leaf margins turn red or yellow, but they soon turn brown and drop prematurely. The bacteria Xylella fastidiosa causes this disease, which leads to a five- to 10-year period of dieback, decline and death. Proper watering and fertilizing can help an infected tree live longer. Eventually you can hire a landscaper to remove a dying, heavily infected pin oak. Plant different tree species together to prevent the disease from spreading. Leafhoppers and spittlebugs spread this disease, so you should remove weeds that provide a habitat for these bugs. A certified professional can inject the antibiotic oxytetracycline to control symptoms, but this expensive option will not cure the disease.
Anthracnose is a fungus disease that infects pin oaks during wet weather. Light brown patches appear near the veins of infected leaves, and eventually blend together. The brownish leaves drop prematurely. If these symptoms occur several years in a row, you can spray the tree with a mixture of 2 teaspoons of chlorothalonil-based fungicide in 1 gallon of water in early spring to help the tree recover. To protect an infected tree from moisture stress, spread a 2- to 4-inch layer of wood chips or other organic mulch around the tree as far as the branch canopy, but do not place the mulch against the tree trunk. Water the tree when the soil is dry until the top 6- to 8-inch layer is moistened. In the fall, rake and dispose of leaves, and trim dead twigs.
If a pin oak has wrinkled, pale leaves, it may have early symptoms of oak wilt. As this disease progresses, the outer leaves wilt and develop brown margins. The entire leaf eventually turns brown. These symptoms work their way to the center of the tree, until the tree dies from the disease. A professional tree care company can cut underground roots to prevent oak wilt from spreading to uninfected trees. Tree care professionals may be able to save a tree by injecting propiconazole fungicide and pruning infected branches. Treatments may save a tree if no more than 30 percent of the tree is infected, states the University of Minnesota Extension.
During a drought, pin oak leaves may turn brown as the tree goes dormant to conserve water. Prevent drought stress by providing 3 inches of water every two weeks, preferably from a sprinkler that lets the water gradually soak into the soil. Drought stress, frost or waterlogged soil can lead to fatal oak decline, which is caused by armillaria root rot and the two-lined chestnut borer. Symptoms last two to five years and include dieback and sudden leaf wilting and browning without leaf drop. Proper cultural practices such as mulching and watering helps trees resist oak decline. A tree care professional can inject the insecticide imidacloprid to control the two-lined chestnut borer.