What disease is causing my oak trees to have brown leaves? ASK THE HORT AGENT
Question What disease is causing my oak trees to have brown leaves?
Answer An ailing oak tree is certainly cause for concern. In nature, very few of the hundreds of biotic agents that attack oaks can cause the death of a mature tree. Insects and pathogens that attack leaves and twigs sometimes create obvious damage, but their effects are more disconcerting to people than damaging to the trees. Oak trees didn’t earn their “mighty” reputation by bowing to the threats of every little bug and disease.
The cool spring followed by rainy hot weather has created a great environment for one of North Carolina’s most common diseases. It is called oak anthracnose. White oak is the oak species most susceptible to this leaf spot disease. Oak anthracnose may look bad, but it does not permanently damage vigorously growing trees.
Raking leaves and pruning dead or dying branches helps reduce the number of new infections the following year. Spring fertilization of severely stressed trees may also improve tree vigor. Fungicide sprays can be applied using a helicopter, but this control tactic may be cost prohibitive for most homeowners.
Oak anthracnose is sometimes confused with oak wilt, a deadly systemic disease of oak trees. All species of oak are susceptible to oak wilt, with red oaks being most vulnerable. Oak wilt is almost always lethal and death can occur in as little as one month. There is no known cure and the best way of dealing with oak wilt is to isolate and destroy the affected trees. This disease is primarily found in midwest states. Although there have been cases of this disease confirmed in the mountains of North Carolina, it is not commonly found in the Atlantic coastal states.
By far, the disease that kills the most trees is man. Isn’t it ironic that the caretaker of the trees is also the primary killer (maybe the butler did do it)? The fine balance that exists between oaks and their insects and pathogens can easily be knocked out of kilter by various human activities.
Damage, stress, and harmful cultural practices may take many years to kill an oak, but once initiated the process of decline is generally irreversible. People fail to make the connection between construction disturbances and the eventual decline (death) of their oak trees. When dealing with existing oaks incorporated into developed areas, "Why did this oak die?" is often less of a wonder than "How did this oak survive?"
If you want more info about tree diseases, then visit this website http://pubs.caes.uga.edu/caespubs/pubs/PDF/B1286.pdf If you do not have internet access, then call me at 910-893-7533, write me at PO Box 1089, Lillington, NC 27546 or email me at gary_pierce@ncsu.edu
Contact me if you need your trees sprayed, so I can begin my helicopter flying lessons. I’ll fly if you buy (the helicopter and the lessons).
Gary L. Pierce
Horticulture Extension Agent
Harnett County | 
