Grub Treatments in Fall
Damage from white grubs in lawns can show up anytime after mid-August. However, our experience has been that grub damage does not become obvious until September or even into October. Damage from grubs is usually localized.
White grub damage may first appear as drought stress (gray-green discoloration and wilting in the hot sun). More severe damage causes the turf to die in large irregular patches that can be rolled back like a loose carpet. High populations of grubs may go unnoticed until discovery by raccoons or skunks.
Treatment for white grubs in late summer is problematic. It is not an automatic decision to choose to use an insecticide for white grubs. By September white grubs are fully-grown and thus harder to kill. The best treatment may kill only 60% of the grubs. Severe damage to turf may have already occurred. If raccoons have found the grubs they will continue to return and cause additional destruction. In many cases it may be preferable to repair the damage through seeding or sodding without treating. If the old loose sod is still green it may reattach with adequate watering.
Insecticide treatments after early October are not effective and are not recommended. If you do treat it may not be necessary to treat the entire lawn. Treat grub “hot spots” determined by observation or sampling. Presently, trichlorfon (Dylox or Bayer 24-Hour Grub Control) is the fastest-acting, most effective homeowner insecticide for curative grub control.