Spring is almost upon us and overwintering white grubs will soon be emerging from the depths to continue feeding for a short time before they pupate. These overwintering grubs typically spend the frigid months of December – February deep in the soil profile (up to 12 inches deep) to avoid freezing. As soil temperatures begin to rise (like they have this month), these grubs “wake up” and work their way into the thatch/soil interface to continue feeding. By mid-April spring feeding is usually in full swing and it is sometimes accompanied by an increase in skunk and raccoon foraging activity that can occasionally damage the turf.
Although it may be tempting to try to manage white grubs during this time, data clearly indicates that the effectiveness of chemical applications targeting white grubs in Spring is greatly diminished. Unless serious secondary damage resulting from animal foraging activity is observed, attempts to manage grubs at this time should be discourage. The window of opportunity and likelihood of success are so small that applications made at this time will almost certainly be wasted.
If secondary damage from animal foraging is simply too much to tolerate, an application of trichlorfon (Dylox) is the only course of action that stands a chance of being effective, and even then the odds are not in your favor. Also, remember that killing white grubs present in April will likely have no impact on white grub populations occurring later this year (July-October).
Instead, consider raking out and re-seeding damaged areas and forget about trying to control these overwintered grubs.
Doug Richmond, Turfgrass Entomologist