Mature larvae cut a hole in the leaf epidermis and drop to the ground. Here they dig one to two inches into the soil to form a pupation chamber. Birch leafminers usually produce two to three generations a summer. Birch Leafminer Larva. Control Strategies Birch leafminers prefer sunny areas but will attack susceptible trees almost anywhere.
Birches tolerate leafminers best when they are planted in shady, cool, moist areas.
Since birch leafminer attacks may weaken the trees, making them more susceptible to borer attack, good fertility and horticultural care are needed. When chemical controls are needed, control of the first generation will generally eliminate any need for additional applications. Since the larvae must find soil for pupation, place a black plastic or tightly woven fiber mulch under the tree drip line. Lightly mulch with organic material so that drying can occur rapidly. Unfortunately, the birches with the finest white bark seem to be more susceptible to the birch leafminer.