White grubs are the larval stage of Japanese beetles. In most cases, brown spots will appear in the lawn in late August to early October, long after the grubs have done their damage. According to Donald Lewis, entomologist for Iowa State University, the severe damage is usually highly localized and is confined to irregular and isolated spots. The damaged areas may first appear as drought stress, with gray to green wilting of the grass. The onset of dry weather can lead to a sudden appearance of grub damage.
Apply a granular insecticide specific for white grubs in your area. Consult your local agricultural extension service as they may have specific recommendations for white grub treatments in your area.
Broadcast the insecticide to the spot areas that show signs of grub damage as described above. Follow all label directions for correct amounts to the spot sections of the lawn.
Water the granular insecticide into the lawn using a sprinkler attachment to the garden hose. In most cases you must add approximately ½ inch to 1 inch of water immediately after spreading the chemical on the lawn.
Continue to water the treated area weekly, to aid in the recovery of the turf.
Spread the correct species of grass seed over severely damaged areas of the lawn. In severely damaged areas, rake the dead grass from the soil. Sow grass seed. Rake the seed into the bare soil to improve soil contact with the new seed. Keep the seed well watered to improve germination and grass growth.