There are three main types of oak trees (Quercus spp.) that grow in U.S. Department of Agriculture plant hardiness zones 3 through 9; white, red and live oaks. All three are susceptible to most oak diseases. Fungi, insects and poor growing conditions can cause leaf curl or scorching. There are a few ways to narrow down the possible cause of the damaged leaves without having the leaves professionally tested.
Examine the edge of the leaf. If there is a distinct line between the healthy green part of the leaf and the browned leaf edge, the tree may have anthracnose, a fungal disease. Anthracnose usually shows up in the early spring.
Look for cankers on the tree bark that may be oozing or bleeding. This accompanying the leaf scorching may indicate Phytophthora ramorum, a fungal disease that can lead to sudden oak death.
Check recent rainfall amounts. Lack of water during drought conditions may lead to drought injury that shows up as brown edges on leaves. Make sure trees have plenty of water during dry periods to prevent water stress or wilt.
Determine when the damage began. If the leaves turned brown in late winter, they may have suffered frost damage. If the damage began in the hottest part of the summer, it may be drought stress. If the leaves began to curl or drop after a wet spring, it could be anthracnose.
Look at the area around the tree. Damage from nearby salt spray can cause leaf edges to appear scorched. Overfertilization of the lawn around the tree can lead to the same type of damage, burning roots and leaving salts in the soil.
Examine the undersides of the leaves for mites. You may need to use a magnifying glass. Mite infestations may cause leaf curl. A mite spray will help eliminate the pests.
- Texas A and M University Forest Pathology: Oak Pathology- Using Leaf Symptoms to Diagnose Recondite Maladies
- United States Department of Agriculture: Sudden Oak Death and Phytophthora Ramorum: A Summary of the Literature
- University of Minnesota Extension: What's Wrong with My Plant
- City of Boulder Colorado: Tree Care During Drought
- UGA Center for Urban Agriculture: What's Wrong With My Tree
- APSnet: Sudden Oak Death and Ramorum Blight
- Aggie Horticulture: Oak
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