by Daniel Frank, WVU Extension Service Entomology Specialist
White grubs are the larvae of beetles in the family Scarabaeidae (commonly called scarabs). Although there are many different species of scarab beetles in West Virginia, the larvae of only a few are considered significant pests. Among native white grub species, the most important and widespread include the masked chafer (Cyclocephala species), May beetle (Phyllophaga species), black turfgrass ataenius (Ataenius spretulus), and green June beetle (Cotinis nitida). Important invasive white grub species include the Japanese beetle (Popillia japonica), oriental beetle (Anomala orientalis), Asiatic garden beetle (Maladera castanea), and European chafer (Rhizotrogus majalis).
DescriptionAll white grubs are similar in appearance except for size, which varies with the species and age. When fully developed, they can range from 3/8 inch to nearly 2 inches in length. Grubs are whitish to cream-colored with a brown head and three pairs of short legs. White grubs are soft bodied and exhibit a characteristic C-shape posture.
Adult beetles are stout bodied, oval in shape, and have clubbed antennae. Depending upon species, they can be green, tan, brown, or black and can range from about 3/16 inch to 1 inch in length. With the exception of Japanese beetles and green June beetles, most species are active during dusk or at night and are not noticed except when attracted to outdoor lights.
White grubs feed below the soil surface on the roots of grasses. Early symptoms of feeding injury include grass wilting or yellowing and the appearance of scattered dead patches of grass. Overtime, dead patches can increase in size and begin to join together. Grass that is damaged by white grubs is loosely attached to the soil and can easily be pulled up or rolled back like a carpet. Damaged areas may also feel spongy underfoot.
Scouting for the presence of white grubs in turf and other grasses should begin early during the grub activity period to determine if the application of a control procedure is warranted. Since white grub infestations are usually patchy throughout an area of grass, several evenly spaced samples should be collected. At each sample site, cut three sides of a square turf section (up to 1 ft2 in size) and peel back the sod. Examine the roots and soil to about 3 in. depth for the presence of white grubs. After examining the soil, replace the grass and water it to encourage regrowth. Finding a few grubs is not cause for alarm. Healthy grass can outgrow the root loss caused by a small number of grubs without showing signs of damage. If areas of grass are dead or dying and grubs are not detected, examine the sod and soil for other causes of injury such as disease, moisture and/or heat stress, excessive thatch, or other insect feeding.
Potter, D. A. 1998. Destructive Turfgrass Insects: Biology, Diagnosis, and Control. Ann Arbor. Press. Chelsea, MI.