Leafspot of Ash and Phyllosticta Viridis

Summary

The foliage of several species of Fraxinus may be affected by a fungus commonly identified as Phyllosticta viridis Ellis & Kellerm. This organism is widely distributed within the United States in the area east of the Rocky Mountains.

In late summer lesions form on the leaves and severe defoliation may follow. The presence of black stromata, protruding from the lower leaf surface, aids in diagnosis. The stromata at this stage have been found to contain both spermogonial and carpogonial locules, and the spermogonial stage is identical with Phyllosticta viridis. The carpogonial locules, each with one or more carpogonia, become transformed, by early spring, into mature perithecia. The perithecial stage has been identified as Mycosphaerella fraxinicola (Schw.) House.

The period of ascospore discharge extends into early summer. Infection is first apparent by the presence of stromata. The evidence in hand indicates that M. fraxinicola does not develop a conidial stage.