White grubs are larvae that emerge from the eggs of the Japanese beetle. In late May or June, the beetle lays the eggs on the top of the soil. Within 50 days, the white grub emerges and burrows underground.
White grubs feed on the root systems of crops and lawns. After the grub burrows 1 to 3 inches underground, it begins eating. Smaller grubs do not do as much damage, but once the grub grows to full size, which is about 3/4 inch long, it can eat more and damage crops and lawns.
As the grubs feed on the root system of crops and grass, crops will die and brown spots start to appear in the lawn. Grubs may attack entire lawns and crops or only certain areas. Cold temperatures of autumn and winter to do not kill grubs, which burrow into the ground past the frost line.
As the grub feeds on the root system, it grows bigger. In spring, the larva enters the pupa stage, during which it is resistant to insecticides. In June or July the pupae emerge from the soil as beetles, and the cycle begins again.