Its relatively compact branching habit commends it for hedges. The tree lilacs, Syringa amurensis and S. amurensis japonica , become small trees, sometimes 25 feet tall, with huge panicles of white, privet-like flowers blooming in early summer. They are speculator in bloom and the foliage is pleasing all season. Pests Several insects and diseases attack lilacs but only a few inflict severe injury. The most common pests are oyster-shell scale and San Jose scale.
Heavy infestations weaken the flower-bearing stems.
They are easily controlled by spraying, during dormancy, with miscible oil or lime-sulfur. Borers usually attack weakened, older stems but may cause trouble on normal, healthy plants. They can be dug from the stems or killed by probing the burrows with a wire. If burrowing is extensive, cut and destroy the infested stems. Mildew may appear on leaves in August and September.