What is causing odd growths on the leaves of my apple tree? - Cooperative Extension: Garden and Yard - University of Maine Cooperative Extension

Question: As I was inspecting/removing aphids from our young apple trees, I noticed an odd growth on a few of the leaves of one of the trees (a native bred Black Oxford from our local orchard and nursery). My inclination is to cut off any affected leaf to keep this odd growth from spreading, but read more