White grubs, however, are among the most difficult soil insect pests to control. Large grubs are highly resistant to insecticides. More importantly, since grubs feed in the soil, it is very difficult to get adequate amounts of insecticide into the root zone to contact the white grubs. Under typical conditions, control of white grubs often fails to exceed 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.
Treatments made in conjunction with soil aeration should increase the effectiveness. Proper watering can improve performance of certain insecticides. For example, post-treatment irrigations are recommended following use of Dursban and Oftanol sprays to reduce the amount of insecticide that remains on leaf tissues. 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. Furthermore, excess watering increases potential problems with pesticide and fertilizer run-off.