The adult flight of southern white chafer peaked during the last weekend in June at The Morton Arboretum in northeastern Illinois. In central Illinois, adult annual white grub numbers are very high in some areas but may still be climbing in others. Japanese beetle adults are very numerous in central Illinois and becoming more numerous each day.
Even though the adults of white grubs are numerous, preventive treatments at this time may not be warranted. In many areas of the state, heavy rainfall has kept nonirrigated turf very green and attractive to egg-laying beetles. If this continues for the next two weeks, the resulting white grub larvae may be spread over such large areas, and thus so thinly, that few areas will have high enough numbers to show turf dieback this fall. In addition, damp soils in the past have resulted in smaller grub numbers, apparently due to the grubs dying from fungal diseases. Applications of imidicloprid (Merit, Grubex) or halofenozide (Mach 2) may not be cost effective this year. It may be more economical and environmentally sound to wait until early August to scout and treat areas that have damaging grub numbers. At that time, use shorter acting insecticides such as trichlorfon (Dylox), bendiocarb (Turcam, Intercept), and diazinon.