Emerald Ash Borer is an invasive wood boring beetle that came from Asia and it attacks Ash trees.
This metallic green beetle was originally found in Michigan and Ontario Canada in 2002 and continues to spread across the country. The way that damage is caused is by the larvae feeding internally in the vascular tissue of the Ash tree and interrupts the tree's ability to transport water and nutrients. Some early symptoms are the gradual thinning of the canopy and die-back of the limbs.
As the infestation progresses, the canopy will continue to thin and die back. In later stages of infestation, epicormic or new shoot growth at the base of the tree occurs. There are also visible "D" shaped exit holes in the tree as well as sloughing off of bark. If left untreated, death will occur.