Lilac and ash borers (Podosesia syringae)
Pest description and damage The lilac borer, also called the ash borer, is a clearwing moth that attacks lilac, privet and other members of the olive family. The adult moth ranges from 1 to 1.25 inches in length and resembles a paper wasp, with orange and yellowish markings on a black body. Initially a thin wet stain forms around the entry hole, but later a mix of frass and sap forms. Areas around the entry site may become sunken and frass and sawdust may accumulate around the base of plants. Eventually, plants show branch dieback, weaken or die. Borer holes are also entry for turkey-tail fungus (Trametes versicolor), which can further damage plants. Damage may be swift or slowly progressive.
Biology and life history Adult clearwing moths emerge in spring from a round hole at the top of their gallery. They mate and lay eggs on the bark at the base of plants and the young larvae tunnel under the bark.
Pest monitoring Deploy pheromone traps in spring to determine when the moths emerge. Watch for wet sunken areas in the bark at the base of the tree/bush. Often the pupal case will still protrude from the exit hole. Spotting even old damage will provide some indication of how heavy the infestation is and inform the next season's strategy.
Pheromone traps are available for this pest and will attract males thus preventing mating. Prune out infested branches during fall or winter when moths are not active as the moths often seek out injured areas on the bark. (Do not compost as moths may still emerge). Insert a knife or wire into the borer hole to kill larvae and pupae. Be sure to make good pruning cuts to speed wound closure.
Entomopathogenic nematodes are available. They are sprayed at the base of trees over entry wounds so the nematodes can find their way into the galleries.
See Table 4 in:
Chemical Control of Landscape Pests
For more information
See "Wood Borers" in:
Missouri Botanical Garden. Lilac borer and ash borer (http://www.missouribotanicalgarden.org/gardens-gardening/your-garden/hel...)