Ash trees decline for a variety of reasons, and not just because of the emerald ash borer.
Reminder: Emerald ash borer has only been found in Allamakee County in Iowa. See the Emerald Ash Borer Team news release for January 17, 2013.
Declining, dying or recently-killed and cut ash trees will be infested by a variety of native borers. The most common is the flatheaded appletree borer (Chrysobothris femorata) that attacks a wide variety of hardwood trees. The larvae create galleries of scooped-out tunnels and chambers just under the bark. See photo below.
Ash bark beetle larvae are about one-eighth inch long and feed between the bark and the wood creating a feather-like pattern of parallel tunnels.
Spray treatments for these borers are not practical. Maintaining tree health and vigor is our best management option.