WHITE GRUBS IN ONTARIO LAWNS

White grubs are common pests  of lawns and turf grasses in Ontario. The white grubs are the larval stage of scarab beetles (Coleoptera, Scarabaeidae), which feed on the roots of grasses and other plants. This feeding results in the wilting and death of the grass in irregular shaped patches on the lawn. The wilted grass can be easily pulled free due to the destruction of the root system. Secondary damage may occur due to animals such as skunks, raccoons, and other small mammals digging up the lawn to feed on the grubs. The damage to lawns resulting from white grub infestations can be quite severe.

The white grubs have white bodies that range from 4 mm when newly hatched to 40 mm for mature June beetle grubs. The grubs have six legs and normally curl their bodies into a characteristic "C" shape. The head is a reddish to brown colour. The tail end of the grub may appear a darker brown to black colour due to soil the grub has ingested during feeding. To tell the different types of grub apart, you must examine the grub's raster, which is a spine covered are on the underside of the tail. The pattern of spines on the raster varies with each type of grub.  Following are descriptions of the three most common types of white grub encountered in turf in Ontario.

European Chafer (Rhizotrogus majalis)

The European chafer is an introduced species, native to Western and Central Europe. It is the grub which can cause the most serious damage turf grass in Ontario. The distinguishing feature of the European chafer grub is the two rows of spines on the raster that diverge towards tip of the abdomen. Mature grubs can reach approximately 25 mm in length.  The mature adult beetles are approximately 14 mm long and a tan colour. The adults swarm in large numbers around trees at dusk in late June and early July, but will not cause significant feeding damage to plants or trees.

In the normal life cycle of the European Chafer, the adult females lay eggs in late June to early July (figure 3). The eggs hatch in late July and larvae mature by October, when they move down into the soil to overwinter. In March or April, the grubs return to the surface and resume feeding. In early May, the grubs pupate and develop into the adult beetle, which emerges in late June to mate. Less than 1% of the grubs may remain in the larval form through their second summer and emerge the following June.

The June Beetles (Phyllophaga spp.)

June beetles are native to North America. The grubs of the June beetle grub can reach a length of 30 to 40 mm, and have 2 rows of parallel spines on the raster.  Adult June beetles are a shiny, reddish-brown to black, oval shaped beetles, reaching 20 to 25 mm in length. The adults fly at night in late May or early June. The adults may inflict very minor feeding damage to broadleaf trees.

The life cycle of the June beetle is more complex than European chafers, taking three years for the insect to reach maturity  (figure 5). Eggs are laid in late May to early June. The eggs hatch within a few weeks, and the 1st instar (or larval stage) feeds through the rest of the summer. In the fall, the larva develop into the second instar, which moves deeper in the soil for the winter. The second instar returns to the surface in the spring and feeds throughout the summer. This second instar is the life stage responsible for the most severe damage. In the fall, the grubs again retreat deeper into the soil, returning to the surface in the spring as the third instar. The third instar feeds for a short period of time in the spring, then pupates into the adult. The adults remain dormant in the soil until the following spring, when they emerge from late May to early June to mate.

Japanese Beetle (Popillia japonica)

The Japanese beetle grub is the least common of the grubs encountered in Ontario, occurring primarily in the Niagara peninsula-Hamilton region. The Japanese beetle is also an introduced species, native to Japan. The grub of the Japanese beetle is smaller than June beetle or European chafer grubs, remaining smaller than 25 mm in length. The spines of the raster are arranged into a "V" shape.

The adult beetle is a metallic green colour, with copper coloured elytra (wing covers) and six tufts of white coloured hair along each side. The adults can reach 12.5 mm in length.

Eggs are laid in late July to Early August. Newly hatched grubs feed on roots into October before moving deeper in the soil to overwinter (figure 6). In the spring, the grubs again feed in the early spring until early to mid May, when they pupate. The adults emerge in July to mate. The adult beetle may cause considerable feeding damage to shrubs, flowers, and fruits.

Controls

Healthy lawns may resist feeding damage by the grubs. Refer to the Ontario Ministry of Agriculture and Food (OMAF) factsheet titled "Lawn Maintenance" (03-059) for information on promoting healthy lawn growth.

The nematode Steinernema carpocapsae is a parasite of white grubs. It is available for use in Ontario as a biological control for white grub. The use of this nematode control agent requires that the soil be kept very moist to support the nematode growth. It is very important that the application instructions for this product be followed closely, as nematodes are living organisms that can be killed through improper handling, rendering the control ineffective.

Insecticides registered for home use to control white grubs are chlorpyrifos and diazinon. Read and follow the directions for use on the label of the insecticide container. Chemical treatments should target the grubs when they are newly hatched and feeding near the surface to be most effective. The appropriate time to apply the insecticide is dependent on the type of white grub causing the damage, therefore accurate identification of the type of grub is required.

It is important that the lawn be watered heavily just after the application to move the pesticide down into the soil where it will come in contact with the grubs. Thick thatch may bind the insecticide, preventing it from reaching grubs, reducing the efficiency of the control.  White grubs will retreat deep into the soil during cold or dry conditions. Any spraying under these conditions will not be effective. It is best to wait until there are warm temperatures, when the weather has been wet or the lawn has been watered heavily before treating the lawn. Under these wet, warm conditions, the grubs will be actively feeding near the surface, and more susceptible to the pesticide.

In the spring, the grubs of all three species are mature, or are in their dormant pupal stages, and are more resistant to insecticides. Treatment in the spring will not be of benefit as the grubs present will have already finished feeding, or will be less susceptible to controls. Depending on the species, treatments should be delayed until later in the season, when the next generation of grubs is present.

For the European chafer, monitoring should begin in mid August and continue through September. Monitoring is accomplished by peeling back the sod, or cutting small pieces from the lawn to lift away. If the number of grubs found under the turf is more than 5 to 10 per 0.1 m2 (1 square foot), control measures are appropriate. The grass removed during grub monitoring will recover if simply replaced in the hole, gently patted back into place and watered.

For June beetles, monitoring should begin in early June, just after the adults cease their nightly flights. Grub densities of 3 to 5 per 0.1 m2 (1 square foot) may require treatment. Treatments will be most effective at killing the first year grubs.

Controls for Japanese beetles should begin in July, after the peak of beetle mating. Adult Japanese beetles may be captured using commercially available traps, baited with insect pheromones and other attractants. Spraying of the adults beetles with insecticides is possible, but will only result in short term control.

J.B. Stewart

References

Anderson, A., and J. Eggens. 1987. Lawn Maintenance (Factsheet 87-077). Ontario Ministry of  Agriculture, Food and Rural Affairs. Toronto, Ontario.
Leslie, A.R., 1994. Handbook of Integrated Pest Management for Turf and Ornamentals. CRC Press Inc. Ann Arbor, Michigan. pp. 230- 235.
Sears, M.K. 1984. Grubs in the Lawn (Factsheet 84-049). Ontario Ministry of Agriculture, Food and Rural Affairs. Toronto, Ontario.
Sears, M.K., T. Hsiang, and P. Charbonneau. 1996. Diseases and Insects of Turfgrass in Ontario: A Handbook for  Professional Turf Managers. Ontario Ministry of  Agriculture, Food and Rural Affairs. Toronto, Ontario. pp 17-22.
Vallani, M.G. Relations Among Soil Insects, Soil Insecticides and Soil Physical Properties In: Turfgrass TRENDS. September 1995. pp 11-16

PDCF-001 (Revised 04/03/10)