Pest or disease

[DeeBee]

Does anyone keep if this is a pest or disease on my hardy garden hibiscus?

 

[Mike Allen]

Not a fungal problem that I readily recognise. Mallows are usually trouble-free in this respect. I am wondering if the leaf of your hibiscus has been adopted as a nursery for some spider or other visitor. If in doubt, remove the affected leaf and keep if for a while, say, in a glass jar and observe. Otherwise, remove and burn.

 

[Marck]

This is a rust fungus, most likely Hollyhock Rust (Puccinia malvacearum) which affects many members of the Mallow Family (Malvaceae) including Hibiscus.