I planted some apple trees from 2-3 yr old nursery stock for the first time this spring. They are mulched beyond the drip line, and I've been making sure they get about 2-5 gallons of water/week. They were doing ok, but recently I'm starting to see what looks like something eating away at the leaves (see example http://i.imgur.com/poJ3nG2.jpg). The month of June and beginning of July was quite wet/rainy. Does anyone have any idea what this is?

Here is a link that might be useful: {{gwi:119281}}