Large infestations, of several dozen grubs per square foot, may be needed to cause visible injury. The small, black adult beetles are often seen flying at dusk during midspring and again in early summer. The most important means of limiting grub injury is to grow a vigorous lawn. Healthy, well-watered lawns can tolerate grub feeding more easily than weakly growing lawns. 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.