(Podosesia syringae)
The lilac borer is the larva of a brownish, clear-winged moth that resembles a wasp. Moths may be seen flying around the plant in late spring. The moths lay their eggs in cracks or bark wounds at the base of the stems. The cream-colored larvae bore into the wood and feed on the sapwood and heartwood. The stems become swollen and may break where the larvae are feeding. Their feeding also cuts off the flow of nutrients and water through the stems, causing the shoots to wilt and die. The larvae spend the winter in the stems. In the spring, they feed for a few weeks before maturing into moths. Several other borers may infest lilac.
Before the moths emerge in the spring (April to May), cut out infested stems to ground level and destroy them. In late April, spray or paint the trunks and stems with an insecticide containing lindane. Repeat the treatment 2 more times at intervals of 7 to 10 days. Borers can also be destroyed by injecting liquid insecticides into the holes with an oil can. Holes should then be plugged with putty or a caulking compound. Or kill borers by inserting a flexible wire into the borer hole in early summer. Avoid pruning during the spring months when moths are present.
Plant Care for Syringa