Ohio State University Extension Fact Sheet

Entomology

1991 Kenny Road, Columbus, Ohio 43210-1090

White Grubs in Turfgrass

HYG-2500-95

Species

White grubs (grubworms or simply, grubs) are the C-shaped larvae of a large group of beetles called scarabs. Many species of scarabs are found in the United States and several of these attack turfgrasses. The most important species are: Japanese beetle, Popillia japonica Newman; May or June beetles, Phyllophaga spp.; northern and southern masked chafers, Cyclocephala spp.; and black turfgrass ataenius, Ataenius spretulus (Haldeman). Other, more localized, white grub pests are: European chafer, Rhizotrogus majalis (Razoumowsky); the Asiatic garden beetle, Maladera castanea (Arrow); and the green June beetle, Cotinis nitida (Linnaeus).

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 all areas of Ohio (and generally east of the Mississippi River). The European chafer, Asiatic garden beetle and Oriental beetle are more recent introductions to Ohio and these pests are commonly encountered in counties bordering Lake Erie. The green June beetle is a native pest that seems to be causing more damage in Ohio's southern counties. The black turfgrass ataenius can be found throughout the state 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 in Ohio but some southern species have annual cycles. 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. (See: Identification of White Grubs in Turfgrass -, HYG-2510).

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 favored by the adults 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: Natural Controls - Parasites - Several parasitic wasps, Tiphia spp. and scoliids, attack white grubs and may effectively reduce populations in certain areas. Masked chafers and green June beetles are the species most commonly attacked in Ohio. However, these parasitic wasps may take two to three years to build up effective populations during which time turf damage may occur.

Option 4: Biological Control - Milky Diseases - Several strains of the bacterium, Bacillus popilliae, have been found that attack white grubs. However, the commercial preparations of this bacterium is extracted from Japanese beetle grubs and is most active against this species. This bacterium is picked up by feeding grubs and it causes the body fluids to turn a milky-white before grub death. Fresh bacterial preparations should be used and three to five years are needed to provide lasting controls. Unfortunately, recent studies in Kentucky and Ohio indicate that the currently available products have not performed well in our soils.

Option 5: Biological Control - Parasitic Nematodes - Insect parasitic nematodes in the genera Steinernema (=Neoaplectana) 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. At present, available strains do not appear to be effective from one season to the next. Check with state extension specialists for current information on strain efficacy and usage.

Option 6: Chemical Control - Preventive Pesticide Applications - Since white grub occurrence is rather sporadic, applying pesticides for control of anticipated grub populations is not recommended. However, in areas where adult activity has been observed or perennial infestations have occurred, preventive applications may be warranted. Currently, imidacloprid (=Merit), isofenphos (=Oftanol) and isazophos (=Triumph) are the only registered products which seem to have extended activity. In field trials, imidacloprid and isofenphos generally perform best when applied before mid-August, or when white grub egg laying is underway.

Option 7: Chemical Control - Early Reactive Pesticide Applications - Most of the modern soil insecticides have short active residual periods (three weeks or less) and must be used when the grubs are actively feeding. No registered insecticide is 100% effective; they usually kill 75 to 90% of the grubs present in any given area. This is why re-applications may be necessary when grub populations get very high. Timing of treatments is critical for success. You should apply the pesticide when the grubs are small and actively feeding yet late enough to catch all of the population. In general, reducing thatch and using good irrigation after making a pesticide application will increase control.

Option 8: Chemical Control - Late Season Reactive Pesticide Applications - Occasionally, turfgrass damaging population of white grubs may go undetected until September or October. By this time the annual white grubs are usually third instars and may be 70 to 80 times the body weight of a newly hatched grub. These mature grubs are voracious feeders but are ready to dig down into the soil when cold weather arrives. Chemical control of these large grubs is difficult, at best. If a late season insecticide application is needed, diazinon, isazophos (=Triumph) and trichlorfon (=Dylox, Proxol) have been the most successful. Be sure to irrigate well after the application in order to keep the grubs near the soil/thatch interface and to wash in the pesticide.

Option 9: Chemical Control - Spring Pesticide Applications - As with the late-fall pesticide applications, spring treatments are often ineffective. Though the grubs feed during the spring, they are quite large and the span of time for treatment is short. If a spring application is deemed necessary, check to make sure that the grubs are actively feeding at the soil/thatch level. Diazinon, isazophos (=Triumph) and trichlorfon (=Dylox, Proxol) have been the most effective pesticides at this time.

Maximizing Control of White Grubs with Insecticides

Adult Sampling

Adult activity of May/June beetles, masked chafers, European chafers and Asiatic garden beetles can be monitored using light traps. Useful predictive data can be obtained by monitoring beetle captures one to two times a week. Simply plot the number of beetles collected over the date sampled on graph paper. If the number of beetles collected drops for seven to ten days in a row, you can assume that the peak emergence and oviposition time has passed. Most species have eggs that hatch within 14 to 21 days. Therefore, grub insecticides can be applied three to four weeks after the peak adult activity was noted in order to target the young grubs feeding at the soil/thatch interface.

Pheromones have been identified for Japanese beetles and Oriental beetles. These pheromones can be used in traps to monitor adult acitivty similar to light trap monitoring.

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.

Insecticides and Application

Bulletin L-187 lists the pesticides currently registered for white grub control in turf. An appropriate registered pesticide should be selected according to the current needs and situation. If irrigation is available, liquid applications are very effective; granular insecticides are often more effective where irrigation is not possible. The following summary table contains published data on the performance of currently registered insecticides for white grub control.

Recent studies have established that 95 to 99% of any pesticide used for grub control ends up in the thatch. Pre- or post-irrigation does not seem to change this binding. If the thatch layer is one inch thick or more, the grubs probably will not contact challenging doses of the insecticides.

Several of the grub insecticides seem to be working less effectively in some geographic areas. Grub resistance was suspected but the actual problem has been documented to be accelerated microbial degradation (=enhanced degradation). Modern synthetic pesticides generally degrade rapidly. However, many are subject to additional degradation by bacteria and fungi which use the compounds as food sources. These microbes tend to build up if a pesticide is used continuously. To reduce the chances of creating enhanced microbial degradation problems, use a pesticide only once per season, when needed, and alternate pesticides.

In general, irrigating after an insecticide application is made will improve performance for soil insect control. It is also generally recommended that grass clippings be returned to the lawn for one to two mowings after a grub insecticide application. Do not wait more than 30 days to recheck the grub infestation, especially if the original population was high. If the grub population has not been reduced below six grubs per square foot consider reapplication of another pesticide. Remember, the smaller the grubs the easier they are to kill with insecticides.

Efficacy of White Grub Insecticides - 1976-1994*
Insecticide	Rate lb.ai./a.	Avg. % control	# Tests	Range % control	% of Tests below 70%
Bendiocarb	2.0	80.7	29	21-100	14
(=Ficam, Turcam)	3.0	79.1	21	0-100	14
	4.0	83.5	23	38-99	17
Carbaryl	8.0	74.7	35	13-100	37
(=Sevin) Chlorpyrifos (=Dursban)	4.0	52.0	29	0-96	59
Diazinon	4.0	70.4	16	47-99	38
	5.5	74.5	40	25-100	30
Ethoprop (=Mocap)	5.0	76.7	38	48-97	34
Fonofos (=Crusade, Mainstay)	4.0	71.4	20	8-100	30
Imidacloprid (=Merit)	0.3	93.2	18	64-100	6
Isazofos (=Triumph)	2.0	88.6	60	46-100	12
Isofenphos (=Oftanol)	2.0	82.1	75	40-100	19
Trichlorfon (=Dylox, Proxol)	8.0	76.1	61	0-98	20
* Data from Insecticide and Acaricide Tests (1977-1993) and Arthropod Management Tests (1994-1995), Entomological Society of America.

NOTE: Disclaimer - This publication may contain pesticide recommendations that are subject to change at any time. These recommendations are provided only as a guide. It is always the pesticide applicator's responsibility, by law, to read and follow all current label directions for the specific pesticide being used. Due to constantly changing labels and product registrations, some of the recommendations given in this writing may no longer be legal by the time you read them. If any information in these recommendations disagrees with the label, the recommendation must be disregarded. No endorsement is intended for products mentioned, nor is criticism meant for products not mentioned. The author and Ohio State University Extension assume no liability resulting from the use of these recommendations.