During a normal year, a life cycle can be completed in five to six weeks. In Connecticut, each year there are three generations and sometimes a partial fourth generation. Only the first two generations are considered destructive, because adult females prefer to lay their eggs in soft, young tissue. Leaf surfaces are generally hardened when third and fourth generation adults appear. The birch leafminer may be controlled with sprays containing the recommended materials.
Proper timing is essential to good control.
Sprays should be applied just after the eggs hatch. Eggs of the first generation usually hatch around mid-May and those of the second generation in early July. These dates can be easily remembered as Mother's Day and the Fourth of July. For best results, repeat the application seven to 10 days later. The second spray is needed because all the adults do not emerge at the same time.