Lilac Ash Borer exit holes. This is one of the most common insects damaging trees along the Front Range and also one of the most common things I treat for. Not to be confused with Emerald Ash Borer, this Lilac borer has been present in Colorado for decades.

Generally, trees that are irrigated can recover from even significant damage as long as treatments are begun. The most common treatments are either an annual trunk spray, or a trunk injection that typically lasts two years.


Severe Lilac Ash Borer damage frequently causes the death of the main stem of the tree. Side branches can take over but the form and aesthetics of the tree are significantly impacted.

Smaller trees can be killed outright. Notice the irrigated tree in the background is still half alive while the foreground tree that was not irrigated is stone dead.


More typical Lilac Ash Borer exit holes. The image at the top of the page shows what it looks like when a woodpecker tries to dig the larvae out, but is this image there is little woodpecker activity.

How many Lilac Ash Borer exit holes can you see in this image? If you said three or four, you don't need to get your eyes checked, but I can see 13!