The new leaves have just started curling on my apple, and under the leaves by the new shoots there are apple aphids, have you checked, and can you see any ants travelling up and down it? I have treated with warm soapy water, but am getting a bit obsessed, and have put a glue band round the bottom... the ants like the aphids 'honeydew' so harvests them but the ants also keep other aphid predators away.. I think this is right anyway! if I'm wrong please someone tell me!