A leaf blight disease called Bur Oak Blight (BOB) has been identified in central Minnesota, including Monticello. The disease only affects bur oak trees, particularly those that are mature and naturally established.
Leaf symptoms appear in late summer and look similar to oak wilt disease. The leaves of infected trees will develop purple-brown lesions on underside leaf veins, eventually noticeable on the top of the leaf. Over time large sections of the leaves may die or appear to have a wilted or scorched look.
Bur Oak Blight is slow-moving, and there appear to be methods to control the disease in trees that have been infected.