Some, such as the Japanese beetle grubs, only eat grass roots. Others, such as the Green June beetle grubs, only eat dead organic matter on the surface of the soil at night. Though grubs are primarily a pest of young trees, older trees can also be damaged by grubs if grass growing between rows is suddenly killed because of herbicide applications or drought. The adult beetles feed on the leaves of hardwood trees, especially oaks. They mate and lay their eggs in short grass from May through July.
Grubs are common in old pastures or where grass is kept short through mowing.
During the winter, the grubs burrow several feet deep in the soil to keep from being frozen. When the soil warms up in the spring, the grubs gradually return to the root zone, feeding throughout the growing season. During the winter of their second year, they begin molting to the adult form. They will emerge as an adult beetle the following spring to begin the life cycle again. White grubs damage trees by eating the roots.