Incidence and severity of dieback in birch plantings associated with Anisogramma virgultorum and Marssonina betulae in Scotland

Abstract

Betula pendula and B. pubescens were surveyed at nine Scottish Woodland Grant Scheme (WGS) sites in 2004 to assess the incidence and severity of two fungal pathogens, Anisogramma virgultorum and Marssonina betulae, and their association with crown dieback. Of the surveyed trees, 47% had at least 40% crown dieback, with B. pendula more severely affected than B. pubescens at most sites. Overall, 57% of surveyed birch trees had A. virgultorum and 28% had M. betulae, with the incidence of trees infected with both species varying among sites. Incidence and severity of A. virgultorum were greater on B. pubescens than on B. pendula, whereas the reverse was true for M. betulae. The relationship between incidence of M. betulae foliar disease and sunken cankers was significant, with 83% of M. betulae-infected trees having these cankers. The presence of M. betulae foliar disease resulted in a greater percentage of crown dieback compared with non-infected trees in both birch species, whereas the presence of A. virgultorum caused greater crown dieback in B. pubescens only. Across all sites and both birch species, as severity of infection with either A. virgultorum or sunken cankers increased, so did the severity of crown dieback. This study showed that A. virgultorum and M. betulae appear to contribute significantly to birch dieback at the nine sites surveyed.