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.
The adult moth looks like a blackish - yellowish wasp and causes no damage to plants. It feeds on flower nectar. 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.
This is a clear wing moth that emerges from the trees in May, June and sometimes July. Usually the adults begin emerging about the time Lilacs are finishing their blooming. The female lays hundreds of eggs in her short life time. The eggs are laid on the bark of host plants often near wounds. The eggs hatch in May or June and the caterpillar burrows under the bark where it overwinters. As spring arrives the caterpillar tunnels directly underneath the surface of the bark and pupates. 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.
The best control is done with a trunk spray of Permethrin in May. It will control the caterpillars from entering the trees trunk. Because there is only one flight (or generation) per year it is only necessary to treat one time annually.
Taddiken Tree Company uses a product called Astro (LABEL/MSDS).