Live oak leaves should be flat, dark green and healthy. This allows the oak tree to photosynthesize and turn sunlight into energy for processing nutrients and moving water throughout the structure of the branches, trunk and roots. Black spots on the leaves indicate a serious health problem that affects the overall health and growth of the oak tree.
Anthracnose of Oak Trees
Anthracnose is a serious fungal disease that has the potential to affect live oaks; serious infections may kill the tree. One of the symptoms of an anthracnose infection is black spots on the oak tree. Other symptoms that indicate anthracnose in an oak tree include leaf blotches, dead portions of the leaves between the veins and premature leaf drop. Anthracnose is treated by gathering and removing fallen leaves and branches from around the oak, applying fungicide to the oak tree and pruning severely affected branches.
Sooty Mold of Oak Trees
Sooty mold is a fungal disease spread to oak trees by aphids and scale insects; it causes black spots to appear on the live leaves. Over time, the black spots will spread to cover the entire leaf as the disease progresses and releases more spores into the surrounding atmosphere. Sooty mold is controlled through pruning affected areas and spraying the oak tree with a fungicide, as well as pesticides to control the aphids and scale insects on the tree.
Fungal Leaf Spot Disease of Oak Trees
Phyllosticta fraxinicola is the most common type of fungal leaf spot disease, according to the Oklahoma State University Cooperative Extension Service website. This disease causes large yellow or brownish spots to form on the underside of oak leaves; the spots later develop brown or black centers as the fungus matures and begins to release spores. Remove fallen leaves from around the oak tree and prune branches that have suffered from dieback. Apply a fungicide to the oak tree to kill the remaining spores.
Prevention and Care for Oak Trees
Begin a spray schedule of fungicides in the early spring to prevent fungal spores from infecting the tree. Remove fallen leaves and branches from around the tree throughout the year to keep them from becoming hosts to fungal diseases and the pests that spread them. Taking proper care of the oak tree throughout the spring and summer reduces the likelihood of pest attacks and fungal infections that cause black spots.
- Oklahoma State University Cooperative Extension Service; Anthracnose and Other Common Leaf Diseases of Deciduous Shade Trees; Sharon von Broembsen
- University of Illinois Extension; Fungal Leaf Spot Diseases of Shade and Ornamental Trees in the Midwest; July 1998
- Clemson Cooperative Extension; Oak Diseases and Insect Pests; Joey Williamson; Dec. 2010