In summer, small, yellowish or reddish spots on the leaves (Picture 1). The undersides at the respective sites have initially yellow-brown, later blister-like sporocarps turning black (Picture 2). Severely affected leaves shed.
Rust fungi [Pucciniales]
Rust fungi occur on many ornamental plants. They are mainly seen in unprotected ornamental crops.
Host needs to be eliminated in alternate host rust fungi. In case of infection, repeat pruning of affected shoots. For prevention, treat plants with a fungicide ensuring the spray reaches both leaf surfaces.