Holes, where larval excrement is pushed out and where adults have emerged, are also signs of an infestation. This flatheaded borer occurs in most species of birch. Adult beetles emerge from infested trees in late May and are present until July. They feed on birch leaves for several days before laying eggs under bark and in cracks in the bark. The larvae burrow directly through the bark into the cambium layer.
Heavy infestations cause raised burrows that can be detected on the bark surface.
Adults prefer weakened trees for egg laying. Healthy, vigorous trees usually are less likely to be infested. Cultural practices are very important in the prevention of bronze birch borer injury. They are best suited for shaded, damp situations and should be watered regularly. Plant a ground cover over the root area to keep roots cool and moist.