- Colorful leaf spots and lesions
- Small black pustules on leaf undersides
- Swollen petioles with black pustules
Bur oak blight symptoms develop mid-summer as small circular leaf spots displaying colors of reds, purples, and browns. Next, the major leaf veins start dying and display similar colors. Leaf death occurs in sections or wedges. Small, black fruiting bodies develop the undersides of leaves on the veins. Petioles(the stem of leaves) begin dying and swell at the base. As the disease progresses, the petioles die, turn brown and develop black pustules. Dead leaves remain attached to the tree throughout the winter. Leaves may break off, leaving only the petioles attached.
Repeated defoliation by bur oak blight predisposes trees to secondary problems like Armillaria root rot or two-lined chestnut borer.
Severely affected trees that suffer repeated defoliations early in the summer may die. Tree death is usually caused by the secondary insects and pathogens. Fungicides are not labeled for control to date. Because the fungus persists on the petioles of infected leaves still attached to the tree, removing fallen leaves does not provide effective management.
Pesticides are neither available nor recommended for managing this disease.
