Distribution
White grubs are perennial pests of the cool-season and transition zone turf grasses. May/June beetles, masked chafers and Japanese beetles are found in most areas of Ontario. The European chafer, Asiatic garden beetle and Oriental beetle are more recent introductions. The black turfgrass ataenius can be found throughout Southern Ontario where it is a perennial pest on golf courses.

Damage Symptoms
White grubs eat organic matter including the roots of plants. Therefore, damage first appears to be drought stress. Heavily infested turf first appears off color, gray-green, and wilts rapidly in the hot sun. Continued feeding will cause the turf to die in large irregular patches. The tunneling of the larvae cause the turf to feel spongy under foot and the turf can often be rolled back like a loose carpet. Grub populations may not cause observable turf injury but predatory mammals such as skunks, racoons, opossums, and moles dig in the turf in search of a meal.

Description of Stages
Scarabs have a complete life cycle with eggs, larvae, pupae and adults. Japanese beetles, masked chafers, green June beetles, European chafers, Oriental beetles and Asiatic garden beetles have annual life cycles. The May/June beetles usually take two to three years to develop. The black turfgrass ataenius has two to three generations per summer. Most turf scarabs overwinter as larvae but the black turfgrass ataenius and mature May/June beetles overwinter as adults.

Eggs:
Most eggs are a creamy-white in color, about 1/16-inch (1.5mm) long and slightly oval when first laid in the soil. These absorb water from the soil and swell slightly, becoming more round.

Larvae:
The C-shaped white grubs are thick bodied, creamy-white with brown head capsules and short legs. All species have three instars, that is, the larvae molt three times.

Pupae:
The pupae are often slightly longer than the adults and are formed in chambers one to two inches in the soil. The pupae are first cream colored and darken before the adults emerge.

Adults:
The adults are typical scarabs - robust, oval beetles with the antennae ending in a large club of flattened plates. Most genera are easy to identify by sight but species identification of May/June beetles and masked chafers require a specialist. Identification of Species
The adults are easily identified to genus but the grubs are the stage usually found in the turf. The grubs are identified by the form, shape and arrangement of bristles (the raster) on the last abdominal segments. A 10 to 15 power hand lens is usually adequate for identification and the common white grub groups can be identified using a raster pictorial key.

Control Strategies
White grubs seem to be periodic pests, attacking turf areas irregularly from year to year. The major factor influencing development of damaging numbers of grubs is soil moisture and rainfall. In general, in years with normal or above normal rainfall, grub populations increase. Well maintained turf next to ornamental plants s seems to be more commonly attacked. However, masked and European chafer adults do not feed as adults and these pests build up in well watered and maintained turf. Black turfgrass ataenius and green June beetle adults seem to be highly attracted to turf with decaying thatch layers.

Option 1:
Cultural Control - Host Plant Modifications -
Certain species of scarab adults prefer specific host plants. Where Japanese beetles are common, do not plant roses, grapes and lindens around high maintenance turf areas. May/June beetles prefer oaks and the green June beetles feed on ripening fruit such as peaches. The fine and tall fescues are not as severely attacked as Kentucky bluegrass and perennial ryegrass.

Option 2:
Cultural Control - Water Management -
Practically all white grub species require moist soil for their eggs to hatch. The young larvae are also very susceptible to desiccation. In areas where turf can stand some moisture stress, do not water in July and early-August when white grub eggs and young larvae are present. On the other hand, moderate grub infestations can be out grown if adequate water and fertilizer is applied in August through September and again in May when the grubs are feeding. This latter strategy is not preferred because mammals may dig up the turf or irrigation bans may occur.

Option 3:
Biological Control - Parasitic Nematodes -
Insect parasitic nematodes in the genera Steinernema and Heterorhabtitis have been shown to be effective against white grubs. Field trials of S. carpocapsae strains have generally resulted in less than 50% control, though H. heliothidis strains have achieved 80% control or better.

Grub Sampling
White grub populations should be assessed when the grubs become large enough to be easily seen (August for the annual white grubs and early-June for black turfgrass ataenius). Assess by taking square foot samples several places over the turf area. Square foot samples are taken by cutting through the turf and thatch on three sides of a square. Peal back the turf and inspect the thatch and upper inch of soil for grubs. A more convenient method is to use a standard four-inch golf course cup changer. This equipment cuts a round core that is about one-tenth of a square foot. Take the cores in a zig-zag pattern across the turf area and multiply the average grubs per core by ten to get an approximate number of grubs per square foot.
Populations of annual grub species that are less than six grubs per square foot can usually be masked by water and fertilizers. Populations between 10 and 15 per square foot can cause significant turf damage in September and October. Of course, populations occasionally reach 40 to 60 grubs per square foot and these levels can cause damage by late-August.
Time spent doing grub sampling can usually be reduced by sampling only in the most likely turfgrass habitats. Most of the annual white grubs seem to prefer grass in sunny areas. The night flying species are often attracted to street lights at night and they may lay large numbers of eggs under or near these lights. Black turfgrass ataenius adults prefer to lay their eggs in compacted, moist and decaying thatch. The green June beetle prefers sunny, thatchy turf or areas that have had manure applied as a fertilizer. Japanese beetle adults usually attack high quality turf near favorite food trees and shrubs.