Problem with cherry tree

[pot shadley]

We have a small cherry tree in a large pot that is a couple of years old, and this years has a black sticky mess on the leaves. Any ideas what this could be and how to resolve. Thanks.

[nickdub]

The damage to the leaves is probably caused by aphids. Whatever it is just pick the affected leaves off and bin them, then give the other leaves a good squirt with clean water to wash off any remaining nasties.

[peanut]

Cherry Blackfly/Aphid Cherry blackfly / RHS Gardening Annoying things that I could never get rid of. Didn't cause problems with fruit but looked awful.

[ameno]

It's leaf curl aphid.
Unless it's a very severe infestation then it shouldn't actually do the tree any hard; it just looks unsightly. If the the infestation is very severe then it can stunt the new growth, so it may be worth either trying to squash them or else spraying them.
Check to see aphids are still there, though. They tend to vacate fruit trees and move on to other plants around mid summer, so there's no point struggling to get rid of them if they are already gone. The affected leaves will never uncurl, but that won't really do them an actual harm.

[pot shadley]

Thank you for the replies.