Types

• Oak leaf blister is a disease caused by the fungus Taphrina deformans. All species of oak trees are susceptible to this disease, which usually occurs in the spring. Oak trees become infected through fungal spores carried on the wind or through rain. Once fungal spores reach oak leaves, symptoms of infection will appear in 2 to 4 weeks. Anthracnose is another fungal disease that affects all oak species, but is most common in bur oak. This disease is caused by the fungus Gnomonia veneta, which overwinters in infected leaf litter and plant debris. Spring time weather conditions are favorable for the development of anthracnose and occur most often when daytime temperatures range from 50 to 57 degrees Fahrenheit.
  
  

Effects

• Oak trees infected with oak leaf blister, develop dark brown or green spots on plant leaves which are small, rough lesions. As these dark spots enlarge, the entire leaf may be covered and drop prematurely. Oak trees with this disease often defoliate before the middle of the summer but do not usually die from infection. Anthracnose causes leaf blight, which often has a dark, scorched appearance. Leaves infected with anthracnose often develop dark spots at the leaf tips or along leaf veins. Oak trees with anthracnose may develop a "witches broom" appearance, which is characterized by clusters of dead twigs at the ends of oak tree branches. Wet weather promotes the development of dark lesions, blighting large areas of leaves.
  
  

Cultural Control

• If your oak tree has symptoms of fungal disease, there are ways to prevent it from spreading to other trees in close proximity. Pick up and destroy all fallen leaves and plant debris, as many fungal disease overwinter in dead or decaying plant tissue. Prune out all diseased or cankered twigs and branches and apply adequate amounts of water to prevent drought stress. Applying fertilizers can help keep your tree vigorous and healthy.
  
  

Chemical Control

• Oak leaf blister infections causing severe symptoms in oak trees may require chemical control methods to prevent further damage and the spread of disease. Oak trees with less severe symptoms do not require fungicides for control. Anthracnose is especially damaging to newly transplanted trees, and fungicides should be used as a preventative measure. After bud break, oak trees may benefit from applications of lime sulfur to control of this fungal disease. When applying fungicides, always follow the directions on the label for best results.