White grubs, however, are among the most difficult soil insect pests to control. Large grubs are highly resistant to insecticides. More importantly, because grubs feed in the soil, it is difficult to get adequate amounts of insecticide into the root zone. Under typical conditions, control is often less than 75 percent. Even this amount of control requires a couple of weeks to become evident.
Thatch depth is important to insecticide performance for white grub control.
To a varying degree, white grub insecticides bind to the organic matter in thatch. This prevents them from moving into the root zone to control white grubs. Treatments combined with soil aeration should increase the effectiveness. Proper watering can improve performance of certain insecticides. However, excessive watering does not improve the movement of insecticide into the root zone and can decrease the effectiveness of insecticides for soil insect control.