Issue 17, October 19, 2016

White Grubs

White grubs continue to be a problem in Illinois due to populations rebounding from heavy mortality from droughts and deeply frozen soils in previous years. Due to unseasonably warm temperatures, soil temperatures are still very warm, ranging from the mid-60's degrees F in northern Illinois to the mid-70's in southern Illinois. These temperatures are allowing turfgrass root feeding to continue.

Annual white grubs migrate deeper into the soil when the temperature drops below 50 degrees F. Japanese beetle grubs migrate deeper when the temperature drops below 59 degrees F. If temperatures stay warm, grub damage is likely to continue to occur.

To determine whether insecticide treatment for white grubs will be effective, cut through the sod and pull it back. If grubs are present in the root zone, then treatment should be effective. If grubs are not present, they have migrated deeper and insecticides will not reach them.

Annual white grub larval scouting.

To treat for white grubs at this time of year, use a quick-acting insecticide. Trichlorfon (Dylox) or chlorantroniliprole (Acelepryn) is likely to be the most effective. Also, there is the possibility that turf may be able to grow roots fast enough to stay ahead of grub feeding if it has sufficient water during cooler conditions.

Providing irrigation until the soils cool enough for the grubs to migrate deeper is an option for those who wish to avoid an insecticide treatment. As a result of natural winter mortality, fewer grubs will migrate upwards to feed on this same turf in the spring. Be watchful, however, for a spring drought, which could slow down turf growth enough to allow even a few grubs to cause damage next spring. (Phil Nixon)

Phil Nixon

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