Japanese beetle adults continue to be very numerous in many areas of Illinois. Masked chafer beetles, annual white grub adults, also continue to be present throughout the state. Because the last few weeks have had little or no rainfall and temperatures in the 90s, nonirrigated turf is starting to go dormant. Its growth has slowed, and it is losing its intense green color. This turf is no longer very attractive to these beetles for egg laying.
This makes it more likely that egg laying will be concentrated in irrigated turf and that damage will start showing up in these areas in mid-August. Application of imidicloprid (Merit, Grubex) or halofenozide (Mach 2) to highly irrigated turf by the end of the third week of July is recommended. Scout areas that have received small amounts to no irrigation during the first half of August to determine if there is a need to treat. Any insecticide applied for white grubs should be watered in with at least 1/2 inch of water to maximize control.