One of the most common root-feeding insects that infest lawns is grubs, which are the immature larval stage of several species of beetles. The adult beetles lay their eggs in the lawn turfgrasses that hatch into small, white C-shaped larvae with brown heads and three pairs of legs.
They live underground most of the year until they emerge as adults in the summer months. The beetle species belong to the scarab family of beetles that include masked chafers, May beetles, green June beetles, but the most common grub impacting turf grass stands in Georgia are the ones laid by adult Japanese beetles.
Adult Japanese beetles attack the foliage of ornamental plants, fruit trees, vegetable plants and shade trees in June and July. The Japanese beetle grubs feed on the roots of all types of turf grasses causing the grass blades to turn yellow-brown and die. The lawn may appear to be stressed by lack of water even when adequate amounts are present. The grass sometimes feels spongy and can be rolled back like a carpet exposing large number of grubs in heavy infestations.
The adult beetles lay eggs in the middle of the summer and the larvae hatch in late August. The larvae consume the roots of all types of turf grasses until colder weather arrives at the end of October. They then overwinter.
To control grubs, you need to know the extent of the infestation in the turf. Often they are not present in large enough numbers to be a significant problem for the homeowner. Examine the turf thoroughly. Birds, moles, and other animals digging in the soil are signs of a potentially serious grub problem. These animals often favor grubs as food. Use a large knife or spade and dig out a one square foot section of the sod 4 to 6 inches deep and then roll it back.
Closely examine the upper few inches of soil. Do this test in multiple locations. If you find five or more grubs present, then an application of a pesticide is needed to get the population of grubs under control. Also, take into account the condition, value, and the turf grass used before applying a chemical pesticide. The grubs are more numerous in times of adequate rainfall or when supplemental irrigation is applied, but during periods of droughts they are not as prevalent.
Several chemical pesticides are labeled for controlling grubs. During dry spells, the lawn will need to be irrigated so the grubs will move closer to the surface and then again after the application to get the granular material down into the root zone where grubs are feeding. The label will have specific directions and safety precautions.
Although grubs can ruin the appearance of your lawn, they can be brought under control. Observe the lawn for any signs of their activity and initiate control measures as soon as possible to limit the damage.
Timothy Daly, MS is an Agricultural and Natural Resource Agent with the Gwinnett County Extension Service. He can be reached at 678-377-4010 or firstname.lastname@example.org.