A common turfgrass pest throughout our region, white grubs are the larvae of scarab beetles, most commonly those of Japanese beetles, green June beetles, May and June beetles, oriental beetles and southern and northern masked chafers. These grubs feed on the roots of the grass, which reduces its ability to use water and nutrients. Consequently, heavily infested grass may wilt, thin out, turn yellowish or even die.
Most of these beetles go through a one-year lifecycle. The adults emerge from the ground in late spring/summer (May through about mid-August) to mate and lay eggs on the turf or ground. During this time, some beetles feed heavily on the leaves of trees and ornamental plants — as many gardeners and landscape professionals know, adult Japanese beetles can be particularly destructive, often “skeletonizing” the plants they attack.
In about two weeks, the eggs hatch and the larvae (grubs) move down into the soil surface and begin feeding immediately on grass roots. The grubs are whitish/grayish, C-shaped and soft-bodied. The larvae feed and grow quickly until the first frost in fall, after which they tunnel deeper into the ground to overwinter. As temperatures warm in spring, they rise back up to the grass roots to feed again until they pupate and later emerge as adults.
Now is a great time to check for white grubs in the lawn — while grubs are still small, they are highly vulnerable to insecticide treatments, particularly those that contain trichlorfon (Dylox) or carbaryl (Sevin). Although most turfgrass stands can survive a few grubs, 10 or more grubs per square foot of lawn area indicate a need for treatment. Many different products — typically granular — are available at gardening stores and home-improvement centers. As always, read the product label carefully, and follow all instructions. Note that many products should be watered in after application.