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White Grub

Background

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), May beetle ( Phyllophaga), 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).

Description

All 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.

Damage

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.

Sampling

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 square foot in size) and peel back the sod. Examine the roots and soil to about 3 inches depth for the presence of white grubs. After examining the soil, replace the grass and water to encourage regrowth. However, 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.

White Grubs – Control Measures

Cultural Control

Soil moisture can affect white grub populations and the severity of feeding damage. Since wet periods during July and early August normally favor survival of eggs and young grubs, limit the watering of lawns and turf during this time. However, once the eggs have hatched (around late August and September) increasing soil moisture can reduce feeding damage by encouraging the regrowth of grass roots.

Biological Control

Milky spore disease and insect-parasitic nematodes are two commercially available biological control products available for management of white grubs. Milky spore is a disease that is caused by the spore-forming bacteria Paenibacillus popilliae. Dusts containing the bacterial spores are fatal to Japanese beetle grubs when ingested. This product is not effective on other species of white grubs. An alternative biological control product marketed for control of a variety of white grub species are insect-parasitic nematodes ( Steinernema and Heterorhabditis spp.). These microscopic round worms seek out and kill white grubs in the soil. The effectiveness of biological control products is often mixed because their performance can be affected by a number of environmental factors (e.g., soil moisture, soil type/texture and temperature). Furthermore, it often takes time for their numbers to build sufficiently to control grub populations.

Chemical Control

If white grubs are abundant and causing damage, and non-chemical options have failed, application of an insecticide may be necessary. Rescue treatments with products containing the active ingredient trichlorfon or carbaryl should be applied mid to late August, or when young grubs are present. In areas with a history of white grub problems, a preventative treatment with products containing the active ingredient chlorantraniliprole, clothianidin, imidacloprid or thiamethoxam may be beneficial. These products allow some flexibility in the timing of applications and can be applied a month or so before egg hatch (mid-June to July). Insecticide applications are generally not recommended during the spring since they are not as effective against older grubs. For best results, mow and rake out dead grass, and thatch before treatment with a grub insecticide. All insecticide products should be applied as directed on the label. For more information, please contact your county WVU Extension Office.

White Grubs – Life Histories

Green June beetles, masked chafers, European chafers, Japanese beetles, oriental beetles and Asiatic garden beetles have annual life cycles, meaning they complete one generation per year. Adults mate and lay eggs in mid-summer (June to August). Newly hatched grubs immediately begin feeding on grass roots and organic matter. They continue to feed until around the time of first frost, at which point the nearly full-grown grubs move deeper into the soil and remain inactive during the winter. As the soil warms in the spring, the grubs move back into the root zone and resume feeding until turning into pupae (May to June). Pupae transform into adults and emerge from the soil several weeks later to complete the one-year life cycle.

May beetles (also known as June beetles) typically require two or three years to complete one generation. Adults mate and lay eggs from mid-April to June. Newly hatched grubs feed throughout the summer until the onset of cooler fall temperatures forces them deeper into the soil. As the soil warms in the spring, the grubs move back into the root zone and resume feeding. Species with two-year life cycles pupate by the end of the second summer, typically transforming into adults by late fall and emerging from the soil the following spring. Species with three-year life cycles pupate midway through the third summer, transforming into adults by early fall and emerging from the soil the following spring.

Black turfgrass ataenius have two generations per year. Adults spend the winter in loose soil, leaf litter or other organic debris before emerging in the spring. Beetles lay eggs from May to mid-June. Grubs typically feed for about four weeks before pupating. First generation adults emerge from the soil in June and July to mate and lay eggs. Second generation grubs mature and pupate from late August to September, producing adults that mate and overwinter in the fall.


Author: Daniel Frank, WVU Extension Service Entomology Specialist
Last Reviewed: May 23, 2017