Epidemics of several fungal diseases were observed in Austria during summer and autumn of 1999. Melampsoridium betulinum (Pers.) Klebahn, the leaf rust of birch, caused a premature leaf cast of Alnus incana (L.) Moench on many sites in the Limestone-Alps as well as in the Central Alps. Severely attacked trees lost leaves almost completely during August. In contrast to previous years Betula pendula Roth. and B. pubescens ERH. had a late leaf-fall, but the leaves showed an increasing yellow mottling due to the infection by Phyllactinia guttata (Wallr.) Lev. Tilia spp. was sbuject to epidemic occurrence of Cercospora microsora Sacc. again, causing a characteristic leaf-fall on the youngest leaves by the end of July and August. Rarely, a premature leaf-fall could be observed in the past; this year, even tall trees lost the almost green leaves of the lower half of the crown in early September caused by Phyllactina guttata (Wallr.) Lev. This host reacted very different by birch. The economic aspect of the mentioned diseases can be disregarded. Such epidemics are interesting, when crown-symptoms (as translucent crowns, early defoliation etc.) are mapped and understood as indicators for decreased viability of tree species or stands.
