Phloeospora-leaf spot disease of elms - Phloeospora ulmi
Symptoms / species
Impact / measures
Initially inconspicuous, minute (<0.25mm), characteristically angular, pale green to yellowish leaf spots, with poorly defined margins. On the lower leaf surface in these - often scarcely recognizable spots, conidiomata from which (hand lens!) white shining spore masses emerge as small tendrils which remain after drying. The asexual spores (conidia) are long, crescent-shaped to almost thread-like, colorless and showing several septa. A sexual stage forms in late autumn. The leaf spots turn brown and eventually large parts of the leaf may be discolored. Of the various leaf diseases of the elm, Phloeospora leaf spot is the most common and fairly recognizable by its symptoms.
Affected tree species
The disease often occurs in rainy years but also in damp locations. On the other hand, even severe and repeated infestations have hardly any consequences for the elms. Even premature leaf fall is of no particular importance, since the development of this fungal species occurs in the second half of the year. The damage is purely visual.
Curative measures Generally none necessary. Local conditions that promote the disease (high, long-lasting humidity, e.g. due to dense planting) should be avoided. In urban locations, it is advisable to remove fallen leaves in autumn, as the fungus overwinters in the fallen leaves.