Grubs are C-shaped, with a brown head and white body. The grubs can be 1/3 inch to 1/4 inch long. The grubs are larvae of beetles that hatch and burrow underground. Depending on the beetle variety, the grubs will pupate and emerge as adult beetles from 1 to 3 years after feeding underground. The adult beetle will start the cycle over again by laying eggs in the lawn.
Grub damage can be minimal or severe. Grubs feed on the grass's root system, destroying the grass within that area and causing brown patches in the lawn. Before treating lawns for grubs, property owners must determine if grubs are the cause of the brown patches and the extent of the infestation. Pull back a 6-by-6-inch section of grass 3 inches deep; if there are 3 or more grubs in that area, the infestation needs to be treated. Check at least six to 12 areas of the lawn where brown patches exist.
One of two products applied to lawns will help to prevent grub larvae. Halofenozide and imidacloprid are applied to lawns before the beetles lay the eggs in July. Halofenozide mimics insect hormones and is effective against the Japanese beetle. The product is applied to lawns when the beetles are in flight. Halofenozide has a half life of 129 days; this means that at 129 days after application only half of the chemical remains in the soil. Imidacloprid is applied to lawns when the beetle is in flight and about to lay eggs in July. Applying imidacloprid from April to mid-August is effective in preventing eggs from hatching into grub larvae.
Treating Grub Infestations
Lawns that have grub infestations can be treated with milky spore, which is a non-chemical treatment that doesn’t harm the environment, humans or pets. Milky spores soak into the soil where the grubs feed. As the grubs feed on the roots exposed to milky spore, the grub slowly begins to die. Once the grub dies, its body explodes, sending millions more milky spores into the soil, continuing to protect the lawn and treat grub infestations.