Bronze birch borer is now susceptible to imidacloprid (Merit, Imicide, Pointer) application. Either spraying the bark or injecting beneath the bark with the Mauget, Wedgle, or another injection system should be effective. In either case, the imidacloprid should enter the cambium area in time to control any young larvae before much damage is done. Although it is not too early to treat in northern Illinois due to this insecticide’s longevity, treatment can be delayed for 2 to 3 weeks in that area if necessary. Heritage and other river birch varieties, as well as whitespire, are much less susceptible to this borer than other birches and should not require treatment. Early evidence of borer attack is dead branches at the top of the tree. This dieback progresses down the tree until the tree is dead. Infested trees also have meandering ridges in the bark associated with tunneling in the cambium and 1/8-inch D-shaped borer-emergence holes.
Peachtree borers can be treated at this time in southern and central Illinois with permethrin (Astro, Pounce). Treatment will be timely in northern Illinois in about 2 weeks. Peachtree borer attacks at the base of stressed ornamental Prunus, flowering plum, peach, and cherry trees, causing a thick sap flow near ground level called gummosis. The activity of these borers in the cambium area causes dieback in this area and associated branches on the tree. Lesser peachtree borer also attacks stressed Prunus, producing holes, gummosis, and dieback higher on the trunk and at branch crotches. Although peachtree borer emerges earlier than lesser peachtree borer, permethrin typically lasts long enough to control both species with one application.
Viburnum borers are controlled at the same time and with the same treatment as peachtree borers. There are at least two or three species of viburnum borer in Illinois. The larva feeds in the cambium at and below ground level. Most viburnums are susceptible to attack, but Viburnum opulus compacta is typically the most susceptible. These borers are most prevalent in nurseries and in new landscapes. It is uncommon to find active viburnum borers in established landscape plants, but they commonly have old, round emergence holes near the soil line from previous attacks.