Grub damage can begin to occur between August and can damage turf until late October. If you suspect grub damage, grab a handful of the damaged turf and give a tug. If the turf pulls easily or rolls back like carpet, there is a good chance it is grub damage. We recommend you call us for a free service call if you suspect grubs. Click this link for a video on how to check: http://www.youtube.com/watch?v=1qsptrZGz18