With the hot, dry weather that we have had over the last few weeks, white grubs are popping up in some areas of Illinois. We've had reports of grub problems in the Bloomington, Glenview, Northbrook, and Joliet areas starting a week or more ago. This corresponds to the drier weather reported in northeastern Illinois, which tends to bring grubs into irrigated areas to lay eggs. As in the past, the Bloomington-Peoria area always seems to have some grubs, regardless of the weather pattern. Thanks to Bill Israel of Greenview Landscaping, Jim Fizzell of Fizzell Associates, and the Will County Extension Master Gardeners for the reports.
These infestations are from eggs laid in early July that hatched in late July. While soil moisture was high through August because of earlier rains, the grass grew roots as fast as the grubs ate them. As we got into September, the grubs got bigger and started eating more. At the same time, water became scarce for nonirrigated turf, and temperatures remained high. The normal high temperature for central Illinois in early September is the high 70s, but we experienced highs in the high 80s. Under lower temperatures, bluegrass, fescues, and other cool-season grasses will usually grow, even with only moderate moisture levels.
Control grub damage that shows up due to dry weather, locally high grub populations, or skunk and raccoon activity with quick-acting insecticides so that you will get a quick halt to the damage. Trichlorfon (Dylox, Proxol) and bendiocarb (Turcam, Intercept) will usually kill grubs in three to five days. Diazinon will take three weeks to kill the grubs, but they stop feeding within a few days. Thus, diazinon-treated areas may continue to have live grubs for a while, but damage should stop. Halofenozide (Mach 2) is being aggressively marketed as a curative insecticide and appears to be working in that manner.
Another option for late-season feeding damage, particularly if grub numbers
are moderate (around 10 per square foot), is irrigating under dry conditions. Irrigation will cause the grass to grow faster--hopefully, faster than the rate at which grubs eat the roots. This option will be particularly effective as temperatures drop over the next few weeks, which adds to the fast growth of the grass.