Lilac Ash Borer- Holes in Ash Tree

Lilac Ash Borer is found on the trunks and large, lower limbs of Green Ash and White Ash (also known as autumn purple ash). Usually attracted to trees weakened by drought, poor planting methods, etc.

Identification

The adult moth looks like a blackish – yellowish wasp and causes no damage to plants. It feeds on flower nectar. The pupal cases often times stay intact when the adult emerges and can be seen sticking out of the trunk.

Don’t confuse the round exit holes of Lilac Ash Borer with the D-shaped exit holes made by Emerald Ash Borer. Please see our section on Emerald Ash Borer for more information.

Damage

The larval stage causes the damage to the host plants. They bore into the trunk up to two inches deep and tunnel up to 11″ in length. The damage interrupts nutrient and water flow. Usually one year will create minor stress while repeated attacks over several years can result in breaking limbs and death.

Life Cycle

Adults emerge in spring, mate, and lay hundreds of eggs in their short lifetime. Eggs hatch approximately 9-13 days later and the larvae burrow beneath the bark. Larvae continue to feed until weather cools off where they burrow deeper into the tree to overwinter. As spring arrives, larvae tunnel towards the bark and pupate. As the adult moth emerges, the casting from the pupal stage is often left wedged in the exit hole (1/4″ diameter) and is easily visible by the naked eye. There is only one generation per year.

Control

The best control is done with a trunk spray of permethrin in May. It will control the caterpillars from entering the tree’s trunk. Because there is only one flight (or generation) per year it is necessary to treat only one time per year.