Plant wildflowers to lure parasitic insects, also enemies of beetles. Apply milky spore disease, a biological control for grubs. Use predatory nematodes to control grubs. Nematodes attack while swimming, so pour them on damaged areas with a watering can. Don't use beetle traps, which can attract more than they kill.
Damaged areas are small yellow or brown circles.
Larvae attack roots, so the affected grass can often be pulled up in mats. Peel back a piece of sod. If you see more than 10 larvae per square foot, take action. Use predatory nematodes, pouring them on the lawn, along with water. Add organic matter to the soil to improve water retention.