Stressed trees are more susceptible to these borers and it is best to remove those infested trees. Where lilac borer has been a problem, chemical treatments applied where the bridalwreath spiraea is in late bloom should coincide with the hatching of the new larvae. Ensure good coverage of the bark. Mature larvae are protected from within their feeding burrows and are not as susceptible to chemicals. Rose sawfly and midge larvae have begun feeding on the underside of rose leaves.
Check leaves for first feeding damage.
It begins as small skeletonizing of the leaves. Flip the leaf over and you will find the larvae. They are about 6 to 9 mm in length. Where holes are becoming noticeable in the leaves of dogwood, check the leaf undersides for small, white sawfly larvae. The larvae are about 3 to 6 mm long and chew holes from the undersides of the leaves.