White grubs are the larvae of scarab beetles. The grubs of economic importance in North Carolina are those of the Japanese beetle, the green June beetle, the southern masked chafer, the northern masked chafer, and the Asiatic garden beetle. Several other species, such as May beetles and June beetles, are also present but usually in low numbers. The Japanese beetle is consistently the most damaging grub in this state. Two relatively new pests, the turfgrass ataenius (on bluegrass) and the oriental beetle, are present in western North Carolina. These insects appear to be expanding their range and may become serious problems in the near future.
All these grubs have cream colored bodies with yellow to brownish heads, brownish hind parts, and six legs. Mature grubs vary in length from 1⁄4 to 11⁄2 inches, depending on the species. White grubs usually lie in a curled or C-shaped position. Billbug larvae may also be present but can be distinguished by the absence of legs.
Identifying grub damage can be easier than most other pest or disease. If the soil is very “loose” to where you can basically peel back layers of grass like sod, chances are you’ve just discovered a grub infestation. Most of the times when you peel back the soil/grass you will find grubs lying just under the damaged roots of the fescue grass. Grubs kill the grass from the roots up & arms worms kill the grass from the tips of the grass down towards the roots.
The timing of the insecticide application is critical if control is to be effective. There are two approaches, preventative and curative. Some of the newer products (Merit® and Mach 2®) are preventative, and are most effective when applied prior to when the eggs are laid. This approach should only be used in areas that have a history of grub infestations. The curative approach is used when an existing infestation is detected. The best time to apply curative insecticides is when the grubs are actively feeding near the soil surface. Pesticides applied any other time will be ineffective. This feeding occurs from August through October, and again in April through early May. Curative treatments applied in late summer or fall are usually more effective than spring applications because the grubs are small. Specific timing depends on the species of grub, and on location in the state. Timing of applications in the mountains will generally be later than in the eastern part of the state. Timing of applications for control of the turfgrass ataenius varies.
Another factor affecting chemical control is irrigation. Irrigation prior to application is highly recommended, especially in dry weather. Grubs stay deep in the soil when conditions are dry, and irrigation a day or two before application helps to bring them closer to the surface and improves control. Insecticides kill grubs more effectively if watered in after application. After treatment, green June beetle grubs may be found on the soil surface, whereas other grub species will die in the soil.