Japanese lilac (Syringa reticulata) is an ornamental tree with lilac to white clusters of blooms in the summer. This tree is susceptible to pests when it is stressed by disease or drought. Caterpillars, lilac borers and other leaf miner pests are most common among lilacs, according to Colorado State University. Caterpillars feed on the leaves of the lilac, leaving holes and decaying leaf material behind, while borers tunnel through the bark and leaves of the tree. Regular inspection of the tree will alert you to pests sooner, making recovery a more efficient process.
Remove weeds from near the lilac tree. Apply a weed control product containing Surflan to kill weeds while not harming the Japanese lilac. Follow the label directions. Rake dead weeds away from the trunk and discard them.
Eliminate insects on the tree. Remove caterpillars by hand and discard them away from the tree. Eradicate leaves infected by borers. Detach the leaves near the stem with pruning shears.
Prune the Japanese lilac to allow more sunlight to reach the plant. Sunlight will aide in the removal of pests from within the leaves.
Apply an insecticide containing permethrin to treat the Japanese lilac for boring pests. Spray the bark of the trunk and limbs of the tree. Follow the label directions for the correct application procedure. Apply an insecticide containing carbaryl to leaves infected with caterpillars. Spray the leaves when the caterpillars are young or in early spring for prevention.
Prevent further pest by introducing parasitic wasps into the garden. Maintain a healthy tree to ward off insects and pests. Prune the tree regularly and prevent damage from drought, disease or pruning wounds.