Illinois Natural History Survey - University of Illinois

White Grub Management Options in Turfgrass

The adult beetles tunnel into damp soil beneath turf at night to lay their eggs. Work at the Survey has found that they prefer open sites, laying few eggs under tree canopies. Eggs are laid from late June in southern Illinois into late July in northern Illinois. With these weeks normally being hot and dry in Illinois, the egg-laying adults prefer watered lawns where the grass is green and the soil soft.

Their eggs hatch into C-shaped white larvae with brown heads and six legs. They feed on the roots of turf, causing dieback when their numbers are at least 8-10 per square foot. In the fall, soil temperatures dropping below 50 degrees F will cause them to migrate deeper into the soil for the winter. In the spring, they rise to the turf root zone, feed for a short time, and then pupate, emerging as adults in early summer.

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An annual white grub larva.

Control of these insects has relied on relatively short-lived insecticides such as trichlorfon (Dylox), diazinon, and bendiocarb (Turcam, Intercept). These insecticides are applied in early August when grub numbers are high enough to cause damage. Before treatment, we recommend that grubs be scouted by cutting through the turf with a stout knife, pulling back the turf, counting the grubs in the root zone, and then returning the turf to its original position. Five or six samples should give you a good idea of the grub numbers present in an area.

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Cutting and folding back turf to scout for white grub larvae.

Two newly developed insecticides, imidicloprid (Grubex, Merit) and halofenozide (Mach 2), last for several months once applied. This allows insecticide to be applied in the spring to obtain control in late summer. We strongly urge that these insecticides not be applied until the first half of July. At that time, one can tell whether grubs will be a problem and still allow at least three weeks for the insecticide to activate and become effective. If the adult grub flight is very small or the rainfall is high, such that unwatered turf is as green and lush as irrigated turf, Survey studies indicate that the chances of grub damage are very small and treatment is probably unnecessary. Mach 2 is available only to turf care professionals.

Two biological-type insecticides are being developed against grubs. Cruiser is the brand name for a nematode, Heterorhabditis bacteriophora, that is very effective against white grubs and should become available next spring to turf care professionals. M-Press contains Bacillus thuringiensis japonica toxins that are very effective against white grubs. It should become available in 1998 or 1999. Milky spore disease (Doom) containing the bacteria Bacillus popillae is effective against Japanese beetle but not annual white grubs. It has been difficult to obtain in recent years.

Any insecticide, chemical or biological, should be watered into the turf with at least one-half inch of water to get the material to where the white grubs are located. Remember, reduced or no irrigation during the summer allows the cool-season grasses, bluegrass and fescue, to go naturally dormant. Dormant turf will have reduced growth and be yellowish to brownish in color but will regrow in the fall as rainfall and cooler temperatures return. Unwatered turf is not attractive to white grubs and is very rarely attacked, eliminating the need for all of the above insecticide use. Only prolonged droughts, such as the one last experienced in 1988 in Illinois, are likely to kill the turf.

Philip L. Nixon, Center for Economic Entomology



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