Eggs of our common white grub species (masked chafers and Japanese beetles) need moisture to stimulate hatch. Frequent irrigation in June and July may attract egg-laying female beetles to turf, especially if surrounding areas are dry. High soil moisture also increases egg survival. Turf areas that were irrigated during June and July may show signs of grubs now. In contrast, adequate soil moisture in August and September (when grubs are actively feeding) can help hide root injury.
Irrigated turf can sometimes tolerate 20 or more grubs per square foot before showing signs of injury.
If grub damage starts to appear in late August or September, watering will promote tolerance and recovery. If an insecticide treatment is needed due to extensive grub activity, use products that have 24-hour grub control on the label for best results.
By Lee Townsend, Extension Entomologist