White grubs, the larval form of beetles such as the June bug and Japanese beetle, are a lawn pest in Illinois. These small, white insects live under the soil and eat lawn grass roots, causing it to brown and die. Controlling lawn grubs requires careful maintenance and correct use of insecticides.
According to the University of Illinois, white grubs do most of their damage from the middle of August through early October. They are easy to detect. Simply lift the sod in damaged areas. Infested grass shows small, white grubs at the roots. If there are more than seven or eight grubs per square foot, the lawn needs treatment.
Illinois homeowners who want to avoid chemical use can allow their lawns to go dormant in high summer. Avoid watering the lawn and allow it to brown, and the grubs starve.
If midsummer is unusually wet or brown grass is undesirable, Northern Central Illinois homeowners may use insecticides. The University of Illinois recommends applying imidacloprid or halofenozide in late July, before grub damage appears. Water the lawn before insecticide application.