Rust on an Acer
 

We have two Acer Pensylvanicum Erythrocladum s. The leaves are starting to show
patches (quarter to half an inch long) which are rust coloured, and a very
vivid rust colour at that. Does anyone have an idea of what causes that, and
what should be done to prevent it spreading (or to prevent is occurring in the
first place)?

With thanks

Laurie
Laurie (Laurence) Moseley

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