If you see large, irregular areas of brown, dying grass in your lawn, you likely have a grub infestation. Grubs feed on the grass roots, causing the blades to detach from the roots and the sod to become easily lifted up from the soil like a carpet. You'll usually begin to see the damage occur in early August, when the grubs hatch and begin to feed. Lift up the sod using a spade or shovel in one-foot by one-foot squares to inspect the grub population near the grass roots. If you see more than 10 grubs in a one-square-foot area, you'll need to treat your lawn to control the grubs and their damage.
Treat your lawn grub infestation in early autumn, generally between early August and mid-September. Treat only the damaged or obviously infested areas of your lawn.
Apply an approved grub insecticide to the damaged areas of your lawn. You can use trichlorfon or carbaryl according to the instructions on the label.
Water your lawn immediately after applying the insecticide. Apply ¼- to ½-inch of water to the lawn.
Treat your lawn grub problem non-chemically, as an alternative to using insecticides, with beneficial nematodes of the Heterorhabditis bacteriophora species. Nematodes are microscopic worms that can kill the young grubs. Follow the instructions on the label to properly apply the nematodes to your lawn areas.