Plum leaf cut-out disease

Plum leaf cut-out disease

Observation - Plum leaf cut-out disease. Description: Lots of leaves on my Victoria plum have small discs nearly cut out, but attached on one side. There are circles in the brown disc, but the actual cut-out part can be irregular. My guess is that this is a rust fungus of some kind, but it is distinctive

Lots of leaves on my Victoria plum have small discs nearly cut out, but attached on one side. There are circles in the brown disc, but the actual cut-out part can be irregular.

My guess is that this is a rust fungus of some kind, but it is distinctive and I'm sure will be identifiable. I had thought it might be a eaf-miner but can't see any creature inside.