Annual white grubs and Japanese beetle grubs have hatched. As of August 2, the grubs were still small, less than 1/4 inch long in central Illinois, which indicated that hatching was probably still occurring. With the emergence of adult beetles in northern Illinois at about the same time as in central and southern Illinois this year, the grubs should be about the same size throughout the state. We are finding irrigated turf areas containing 20 grubs per square foot. Damage is likely with 10 or more grubs per square foot, so insecticide application is warranted in watered turf.
Imidicloprid (Merit) or halofenozide (Mach 2) can still be applied through about August 12. The grubs should be killed before causing any obvious damage. For home turf, diazinon can be applied at this time. With its month-long residual control, it should effectively control even late-hatching eggs. Trichlorfon (Dylox, Proxol) kills grubs quickly but has a short residual. All of the grub eggs should be hatched by August 10, so applications of trichlorfon after that date should provide complete control as well.