Field guide to exotic pests and diseases: Blue gum mycosphaerella
Mycosphaerella juvenis Crous & M. J. Wingfield
Leaf spots on blue gum
Source: Mike Wingfield, University of Pretoria, Republic of South Africa
Distribution: Kenya, South Africa, Tanzania, Gambia.
Hosts: Eucalyptus globulus, E. grandis, E. nitens.
Signs: leaf spots on both sides, round to irregular, separate, then becoming joined, 2-12mm diameter, evenly light brown on surface nearest to the leaf axis, whitish brown on surface furthermost from the axis, surrounded by raised borders. Spore containing structure (pseudothecia) under the leaf - single, evenly distributed, black, and globe-like. A number of other species of Mycosphaerella may be associated with leaf blotch diseases of eucalypts.
Likely pathway: seeds, foliage, nursery stock, bark crevices.
Potential impact: infected leaves develop spots, blotches; affected trees suffer premature defoliation; severe infection can cause tree death.