Birch leafminer is present throughout the state. In most parts of Illinois, the damage is light enough that it rarely warrants control, but miners can be a major problem in areas of northeastern Illinois.
These sawfly larvae feed between the top and bottom layers of the leaf. The result looks like a large, brown blotch on the leaf. Birch leafminers are usually attracted to healthy, vigorously growing trees that are able to withstand the damage. Usually, trees that are heavily attacked will continue to be heavily attacked for several years in succession, whereas nearby trees may be almost mineless.
Planting resistant varieties such as river birch (Betula nigra) and dahurian birch (Betula davurica) can reduce problems from this insect. For chemical control, treat at this time when the mines are small and light colored. Systemic insecticides such as dimethoate (Cygon) are particularly effective.