While there are several signs of the presence of Emerald Ash Borer, you’ll be surprised at what people first notice. Woodpecker holes. Apparently ash borer larvae are woodpecker candy, so if you see an ash tree that’s getting a real going over by woodpeckers, you may want to look further.
Other signs of an infestation include die-back at the top of a tree, especially if several ash are planted together and they all look bad; D-shaped exit holes in bark; and sprouts of leaves and branches from the base of the tree.
Of course, the first thing to do when scouting for Emerald Ash Borer is to make sure you are looking at an ash tree. I put this guide up a couple of years ago, which might be helpful in determining if the tree you have is indeed an ash.