Since the grubs work underground they are frequently not noticed. The first indication of damage is generally a gradual thinning and weakening of the lawn followed by small patches of dead or wilting grass even in the presence of adequate soil moisture. Bluegrass is especially susceptible. Damage is often most evident in the middle of August through September. Animals digging up the lawn for the grubs or large numbers of adult beetles being attracted to lights at night may also signal a problem.
Diagnosis requires peeling back areas of lawn with a sharp shovel and looking for the grubs.
If less than six grubs are present per square foot it is unlikely that control is required as the amount of damage caused is minimal. The two most common lawn grubs in St. Louis are the annual grub and May or June beetle. As the name implies the annual grub goes from egg to adult in one year. May or June beetles take two or three years to complete a generation. The grubs feed for two or three years in the ground before emerging as an adult beetle.