White grubs are the larval stage of a beetle known as scarab beetles or more commonly as May/June beetles and masked chafers. White grubs have a characteristic “C” shape, are creamy white, with three pairs of legs and grow to a size of up to 1 to 1¼ inches long.
White grubs feed on grass roots causing severe wilting and eventually death of affected lawns. The sod will tend to lift away when pulled, but grass blades will generally stay intact since the grubs have mainly eaten roots. Additionally, skunks and raccoons in search of larvae will cause considerable damage as a result of their digging and feeding on grubs.
Grubs are generally found in the top inch or so of the soil and will go much deeper during the winter months. Masked chafer grubs have a one-year life cycle overwintering as larvae with the adults emerging in mid to late June.
The May/June beetles on the other hand have a three-year life cycle with adults emerging in May and June, laying eggs and the larvae feeding during the summer and overwintering. The second year, when most of the damage occurs, the grubs feed throughout the summer. In the third year, the grubs complete their development in the spring and early summer forming pupae and adults the following year to start the cycle again.
Control. Many insecticides are labeled for white grub control, however, it is very difficult to control white grubs because of the difficulty of getting the chemical into the soil where they are active. Excessive thatch can impede the movement of the chemical into the root zone where grubs are feeding. Core aeration can help increase the effectiveness of insecticide applications. Proper watering will also help, but it is important not to ove- water. Over-watering can actually decrease the effectiveness of insecticides.
Find additional information on billbugs and white grubs at Colorado State University.