In April and May, mature grubs of the Japanese beetle and other closely related grubs, either as one species or mixed populations, feed on the grass roots, causing the turf to turn brown and die. In summer, the beetles enter the soils of the turfgrass areas and lay eggs that hatch into small grubs. During September and October, with ample soil moisture, nearly full-grown grubs are within an inch of the soil surface or in the soil-thatch interface. They can be equally as destructive to turf as in the spring.