Peel back the grass. Just a couple grubs per square foot are not a problem to an otherwise healthy lawn. Ten or more per square foot are necessary to justify treatment. If the weather is hot and dry, cool season grasses such as Kentucky bluegrass will go dormant. If a few grubs are detected, water and fertilize appropriately so turf can recover from some feeding then reseed or resod areas damaged.
Several pesticides are available for grub control.
Diazinon has been the home gardener's standby for many years. Diazinon is long lasting and effective, but it can commonly take 3 weeks to kill treated grubs. Although treated grubs do little feeding, it can be upsetting to still see live grubs after treatment. Trichlorfon sold as Dylox is an effective pesticide, but it is short lived. Grubs need to be present when this insecticide is applied, but it kills grubs quickly.