Bur Oak Blight
Bur oak blight is a common fungal disease in the Midwestern U.S. Impacting only bur oaks, it occurs most commonly on mature trees. Purplish lesions on the underside of the leaves, along the veins, are the first sign of infection. These lesions then begin to increase in size. Spots of chlorosis, or yellowing, develop and leaves begin to brown and die.
The disease typically gets more severe each year, with greater leaf mortality over time. The loss of healthy leaves makes it difficult for infected trees to adequately produce food. The tree becomes weak and highly susceptible to infestation by secondary pests.
Fertilization to maintain vigor can help trees impacted by bur oak blight. Treatments applied in May or early June, before leaf symptoms appear, can also aid in managing this disease.