White lawn grubs are the larval stage of beetles. According to the University of Rhode Island's website, the adult beetles locate rich green lawns to lay their eggs in July. Most larvae are present by August. Dry summers or lawns with no irrigation will slow the larval developmental process. Having a few grubs in the lawn may not entail any action. Grubs that total more than 12 larvae per square foot will require a method of control.
Sample a section of the lawn between August and mid-September. Cut a 6-inch by 6-inch square section of sod from the lawn turf using the shovel.
Remove the top 3 inches of soil. Count the number of grubs in the removed soil. Grub counts that exceed more than two to three grubs per sample area may warrant chemical treatment.
Take several samples from areas around the lawn. Keep all grubs found.
Take the grubs to your local agricultural extension service for identification. Proper identification will allow the extension agent to recommend the correct insecticide.
Apply the grub insecticide to the infected lawn. Follow all label directions for applications rates. Various insecticides will have different poison strengths.
Irrigate the poison into the soil using the garden hose and sprinkler attachment, if applicable, for that particular product.