Whats wrong with myCoxes Pippin tree

I wonder if anyone can advise me. I planted my apple tree a year ago. It produced lovely apples last year, and there is a pretty good crop this year too. However over the lastthree weeks I have noticed rusty brown patches on the lower tier of leaves. Having looked again today, the branchesseemto havethe same colouring. What could this be? I have looked everywhere for information, but sadly I can't find anything.