We have had reports from Effingham County of widespread dropping of maple leaves due to maple petiole borer. The larva of this sawfly tunnels into the petiole within about 1/4 inch of the leaf blade. As the larva matures, the petiole breaks in this weakened area, and the leaf blade drops to the ground.
One generation of borer is produced per year. Adults emerge in the spring and lay their eggs near the base of the petiole. The resulting larvae tunnel up most of the petiole over the next month. In May or June, the leaf blade drops to the ground, but the larva stays in the petiole on the tree. Later, the larva drops to the ground to pupate 2 to 3 inches below the surface.
Although the number of leaves falling to the ground is large enough to excite the average homeowner, rarely does more than 15 to 20 percent of the leaves drop from the tree. Thus, the impact on the tree is minimal. Raking up the fallen leaves does not reduce the number of insects because the larva stays in the petiole attached to the tree. No control is recommended.