Several borers are susceptible to control in central and southern Illinois at this time. Timely application of insecticide is needed to provide borer control because most are difficult to control once they burrow into the tree.
Bronze birch borer, flatheaded appletree borer, and roundheaded appletree borer are susceptible to an application of imidacloprid (Merit) to the trunk and major branches. Bronze birch borer and flatheaded appletree borer are also susceptible to soil or trunk injections of imidacloprid.
Lilac borer, ash borer, peachtree borer, and viburnum crown borer are susceptible to an application of permethrin (Astro) to the trunk and major branches. Lilac borer and ash borer are the same insect, Podosesia syringae. Because permethrin is not systemic, it is effective only when sprayed on the bark surface to control the egg-laying adults and the hatching larvae before they penetrate the tree.
Lilac borer, ash borer, peachtree borer, and viburnum crown borer are all moths as adults; their larvae are caterpillars. Imidacloprid provides very limited control against caterpillars, making permethrin the insecticide of choice. Bronze birch borer, flatheaded appletree borer, and roundheaded appletree borer are all beetles as adults. Although they are controlled by permethrin, imidacloprid tends to be longer-lasting on the trunk of the tree. This effect is useful because adult beetles tend to live longer than moths. In addition, imidacloprid penetrates the bark, particularly that of younger trees or thinner-barked trees, providing additional control of newly hatched larvae under the bark.