White Grubs

White grubs are the larvae of May beetles, June beetles, mask chafers, and other related beetles. A full-sized larva is about 1 inch long, has a brownish head, three pairs of legs, and rests in a characteristic C-shape. White grubs feed below ground, pruning the roots and causing the grass to yellow. You can easily roll or lift severely damaged sod from the ground by hand. Damage is often most obvious when infested turf doesn’t green up properly in the spring because of heavy feeding by large numbers of large, nearly mature grubs.

The adults vary in appearance, depending on species. June beetles are green, while May beetles are dark brown, and masked chafers are tan to brown. For most species, flights of adults occur early May through mid-June, and egg laying follows shortly. Because white grubs are easiest to control when small, the best time to apply white grub treatments is in mid to late summer. Check for grubs by cutting several 1 to 2-foot square samples 2 to 3 inches deep and lifting out, or rolling back, the turf square to look for grubs. Treatment is probably needed if you find an average of three to five grubs per square foot. When applying insecticides to control white grubs, water insecticides into the turf according to label directions. This leaches the insecticide into the zone where the grubs are feeding.