Bur oak blight (BOB) is a leaf blight caused by the fungus Tubakia iowensis. It is a disease of concern to anyone who has bur oak trees on their property. BOB is most prevalent on Quercus macrocarpa var. oliviformis, an upland variety of bur oak characterized by its relatively small, olive-shaped acorns.
Susceptibility of bur oaks to BOB is highly variable and trees of all sizes are at risk. Occasionally, BOB can infect swamp white oak (Q. bicolor); it is unknown whether hybrids of bur oaks are susceptible. Repetitive defoliation of trees by BOB increases susceptibility to secondary problems such as the two-lined chestnut borer (Agrilus bilineatus) and Armillaria root rot, which ultimately cause tree decline and death.