First Report of Powdery Mildew Caused by an Oidium sp. on Banana Shrub (Michelia figo).

Banana shrub (Michelia figo (Lour.) Spreng.) is an evergreen grown in southern landscapes in hardiness zones 7 to 9. A powdery mildew disease has been observed sporadically on this plant for several years in the Baton Rouge area during fall months, but symptoms were always mild. During the summer and fall of 1998, banana shrub plants were observed with moderately severe powdery mildew infections that resulted in leaf chlorosis, distortion, and some defoliation. An Oidium sp. was present on both leaf surfaces, but sporulation was more abundant on the abaxial surfaces. Conidia were ellipsoid, produced in chains, devoid of conspicuous fibrosin bodies, and averaged 37 × 19 μm. No sexual stage was found. Conidia brushed from infected leaves to healthy leaves of a potted banana shrub maintained in a greenhouse caused new infections in 5 to 8 days. Factors responsible for the increased severity of the disease in 1998 are unknown, but the unusually dry summer may have contributed to the increased incidence of this disease. An Oidium sp. was listed on M. figo in Australia and the United States (1), but no other reports were found to confirm this. This is the first report of the occurrence of a powdery mildew on M. figo in the United States. Reference: (1) K. Amano. Host Range and Geographical Distribution of the Powdery Mildew Fungi. Japan Scientific Press, Tokyo, 1986.