Description
The adults of ash and lilac borers are wasplike moths. The forewings are a brown to chocolate color. The hindwings are clear with a brown border and veins. The body is mainly brown. The legs and abdomen are marked with yellow. The larva is a creamy white, has a light-brown head, and is about an inch long when fully grown.

Click on image for larger version

Figure 1. Adult Lilac Borer

Click on image for larger version

Figure 2. Lilac Borer Emergence Holes in Ash

Life History
The adult female deposits her eggs in cracks and loose areas on the bark of the host plant. Emerging larvae maintain contact with the outside and continue to expel sawdust and frass, which accumulates around the exit holes. The larvae are half-grown when they overwinter. They become active again in the spring, pupating near the end of the burrows. The adults, which are active flyers, emerge in the middle to later part of June in Illinois, There is only one generation a year.

Damage
Infestations by ash or lilac borers result in numerous holes through the bark and wood. The areas around the holes may be swollen, with the bark cracked and broken away and the sap exuding from the holes along with sawdust and frass. Branches may be severely weakened at the feeding site. During dry periods in the late summer, terminal shoots may wilt. Severely affected trees may die.

Click on image for larger version

Figure 3. Ash/Lilac Borer Pheromone Trap

Click on image for larger version

Figure 4. Lilac Borer Larva and Damaged Branch

Nonchemical Control
Protecting newly planted trees from the borers will help reduce problems. Water, mulch, and fertilize the trees as needed for your area. This helps the trees to become established. Water and fertilize older trees to reduce stress. Avoid wounds to the trunk and main branches.

Chemical Control
Insecticidal sprays can be applied to the trunk and upper branches in early June and then 4 weeks later.