Lawn grubs regularly cause damage to yards. Lawns infested with grubs show signs by exhibiting irregular brown patches; often, the turf will detach and peel away from the soil or abundant small dead spots appear throughout. Grubs feed on lawns with no visible damage until the grub population gets out of control. Dig up sections of the lawn to determine if grubs are causing the damage. Identification of the grub type will help determine the control methods needed to eradicate the infestation and return the lawn to health.
The European chafer beetle lays its eggs in lawn and turf grasses in July and August. Twelve days later, the eggs hatch and grayish-white grubs emerge to feed on the roots of the lawn. The grubs grow through three unique life cycles that require molting. With each molt the grub grows and so does its food consumption. During the winter months the grubs burrow deep into the soil to go dormant. When spring arrives, the grubs vigorously feed once more. In late spring, the grubs finally change into beetles, which quickly mate and lay eggs again within the lawn, so the cycle begins again. Carbary or permethrin-based insecticides applied in the fall normally control the grub population according to Cornell University. Follow the directions on the label for application.
The Japanese beetle produces white grubs. The beetles lay their eggs in well irrigated lawns in July. They avoid laying eggs in dry lawns because the grubs do not survive well if the soil is dry, according to Michigan State University. Eggs hatch 10 days after being laid. The grubs appear white and C-shaped. Once hatched they readily consume the roots of the grass. Japanese beetle grubs require one year of molting and growing before they emerge as adults to again lay eggs in the lawn. Control grubs by applying thiamethoxam or chlorantraniloprole prior to July 15.
The May beetle or June bug lays eggs in St. Augustine grass predominately. Grubs emerge from their eggs in the summer or fall. They feed voraciously on the grasses root system. Damage shows up in the lawn one year after infestation. The grubs appear white with an orange head. St. Augustine grass that is infested with grubs often feels spongy when walked on, according to the University of Florida. The grass peels away from the soil as the root system becomes severely compromised. Due to the mild climate that St. Augustine grass grows in, the grubs feed year round. The damage quickly becomes quite severe and may even destroy entire sections of the lawn if control is not gained. Use richlorfon or carbaryl for control late in the season. Apply Merit or Mach 2 in June for early season control. Follow the directions on the label of the pesticide for application instructions.