Fertilize? Now you tell me.
I don't fertilize. Never have, never will. Potted trees get enough fertilizer with repotting - I don't need to add more. As PlantingOaks pointed out, JMs don't like fertilizer.
The leaves in ericscanon's photo are not rootstock leaves. This is a really old variety so reversion is not an issue either.
Its all about available light. Do I need to take photos of mine?