This method produces high-quality plants. The process requires a great deal of knowledge, however, and takes several months in a greenhouse or glass-covered frame, where the air can he kept moist continuously. Cleft grafting is the most common way of propagating the named varieties of lilacs on a commercial basis. And bud grafting is an especially economical and a very rapid method if you want to grow many new plants. A number of insects and diseases attack lilacs, but only a few cause serious injury.
Powdery mildew is the most common disease.
It appears on foliage in late summer, and gives leaves a whitish, dusty appearance. You can control it by dusting with sulfur as soon as you notice the disease. Oyster shell scale and San Jose scale pierce the bark and suck sap from the plant, thus weakening flower-bearing stems. To control scale insects, use either carbaryl or malathion. Lilac borers, as the name suggests, burrow into the wood of the plant, sometimes leaving small amounts of sawdust as evidence of their presence.