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Thanks for the replies I have started spraying the affected leaves and yes they are infected with bug's (black fly) when I was spraying I saw a lot of ladybirds on the tree so perhaps I should stop spraying!!. The tree came from a local nursery at Cews hill here in north London, it was about 5/6 feet high when I purchased it and towards the end of last summer it shot up and now it's covered in cherries some are turning red, when I lived in Manchester I didn't see any in the nurseries I think the weather is a bit warmer further south (more bugs though!!!)