A fungal disease causing leaf damage

Bur Oak Blight is a fungal disease affecting the leaves of bur oak trees in Midwestern states. The disease can begin gradually and build in severity until it kills the tree. The symptoms of Bur Oak Blight might look similar to those found with other conditions of oak trees. High value oaks should be inspected by a qualified arborist for accurate diagnosis.

Infested trees require treatment for control
Bur oaks with Bur Oak Blight can be treated with a combination of fungicidal treatments, delivered as leaf sprays and as a trunk injection. Additional treatments may also be necessary if other conditions affect the tree at the same time.

What to look for
• Purple–brown lesions along middle vein of leaf
• Wedge-shaped areas of leaf yellowing or dieback
• Leaves turning brown and curling
• Black pustules at the base of leaf stalk
• Dead leaves remaining on the tree through the winter

Life Cycle
• In spring, spores are released from the black pustules that developed on leaf stalks the previous fall and winter.
• Rain and wind disperse the spores onto new leaves, and the new infection begins.
• Leaves appear healthy in the early part of the season. Symptoms become visible in late July, August and September.
• Dead leaves and leaf stalks form black pustules and remain on the tree to begin the cycle again the following spring.
• Secondary infections continue throughout the growing season during wet periods

Treatment and Prevention
• Increase plant vigor and disease resistance using:
– Forest Floor Service
– Fertilization with slow released, low-nitrogen fertilizer
– Application of Cambistata tree growth regulator
• Water at ground level only
• Your consulting arborist may prescribe early season fungicide sprays and a trunk injection.
• Affected bur oaks should also be treated against two-lined chestnut borer and other conditions as warranted by the situation

Purple –brown lesions form on midvein of leaf.
Wedge-shaped areas of leaf yellowing.
Symptoms of BOB look similar to those of other diseases.