Lilac borer

Lilac borer larvae tunnel within the trunks and larger branches of lilac trees, creating exit holes in the bark with frass (insect droppings) visible around them. You notice the holes and sawdust-like material on the bark surface during summer and fall months. Internal tunneling weakens branches and can eventually girdle trunks of heavily infested lilacs. Damage becomes apparent by the appearance of emergence holes.

Prune out heavily infested branches below visible damage and burn or bag the material. Make clean cuts to encourage wound healing. Monitor lilac trunks during summer for evidence of fresh exit holes or frass. If borers are confirmed, treat trunk crevices with spinosad or pyrethrin-based insecticides in late June and early July.