There is a chemical treatment available that will kill the insect, but often the borer has done the damage to the tree before it becomes apparent.
It was too late for the young ash tree in front of my house. This summer it produced hardly any leaves, and tell-tale holes appeared in the bark, indicating the Emerald Ash Borer was at work. So it had to go.
Within half an hour, the digger was back with a young tree, It's an Armstrong Maple. It will be tall, and not very wide, and the leaves turn red in the fall, just what I wanted. It took just two minutes to plant, and you can see it here. OlderSon and Callum arrived in time to witness the happy event.
All new family members should have a name, so Callum has christened my tree Mr. Armstrong.