At this time of year, several borers are susceptible to insecticide applications. Flatheaded appletree borer, roundheaded appletree borer, viburnum crown borer, and peachtree borer are susceptible to control when Vanhoutte spirea blossoms have mostly turned brown. Bronze birch borer is susceptible to control when Vanhoutte spirea is finishing bloom. Lilac and ash borer are susceptible when Vanhoutte spirea is in full to late bloom. These phenology indicators are taken from Don Ortonís book Coincide, which is available from the Illinois Society of Arboriculture and also from the publisher, Labor of Love Conservatory, at (630)668-8597.
All of these borers are controlled with one or more applications of chlorpyrifos (Dursban) to the trunk and base of the plant. In addition, bronze birch borer can be controlled with dimethoate (Cygon) concentrate applied once as a band that is as wide as the trunk diameter but no wider than 6 inches.