Grub damage is most prevalent during the fall and early spring when they feed on your lawns' root system. If not treated they will continue to feed on the roots and cause those areas in your grass to die. If you have damage we recommend you treat with a contact insecticide application to control what is in the lawn now, and then treat your lawn with a preventative application in June and July to control the new population that will hatch in early fall. The preventative will control the grubs during the fall and following spring when the damage occurs.
The picture shows the life cycle of a typical grub: