rust diseases
Order Pucciniales
Fungal leaf diseases, among the most damaging pathogens in agriculture and horticulture. Among trees, rust diseases are prevalent in poplar (Populus spp.), willow (Salix spp.) and birch (Betula spp.). They are characterized by orange spore-filled pustules on the leaves in late summer.
This definition is abridged from A – Z of tree terms: A companion to British arboriculture.
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