Posted by Mike on September 24, 2002 at 18:16:00:
In Reply to: lilac bushes with sawdust underneath posted by Barb on September 24, 2002 at 11:49:40:
Sawdust is often found around holes in the stems and on the ground below infested stems.
The lilac borer, a.k.a. ash borer, is the larva of a brown colored moth. The moths lay their eggs in the cracks or wounds at the base of the stems. The larvae bore into the wood and feed on the sapwood and heartwood (source of food and water transportation for the plant). The larvae spend the winter in the stems and mature to moths in spring.
The solution is to cut out infested stems, in spring before the moths emerge, to ground level and destroy the stems. In late April spray or paint the trunks and stems of the plant with a borer/miner spray. Repeat the treatment two more times, once a week for two weeks. Avoid wounding the shrubs with lawn mowers.