White grubs may be the most damaging turf insect pests in the United States. According to the U.S. Department of Agriculture, Japanese beetle grubs alone cause an estimated $234 million in damage each year— $78 million for control costs and an additional $156 million for replacement of damaged turf.
Japanese beetle and masked chafer adults are attracted to turf with moist soil which means they are especially attracted to lawns that get watered during hot dry spells. During the feeding period, female beetles intermittently leave plants, burrow about 3" into the ground— usually into turf— and lay a few eggs. This cycle is repeated until the female lays 40 — 60 eggs. Moist soils are certainly easier to dig through than hard, dry soils. Eggs will dry up and die under very dry soil conditions. The eggs also die when soil temperatures are around 90°F. Higher soil temperatures are typically associated with drier soils, as well as high air temperatures.
White grubs are the larval stage of many different beetles, including the Japanese beetle. The grubs live below ground and feed on the roots of tender grass plants that soon kills the plant. They are most destructive mid-late summer, but the damage they cause may not show up until early fall and by then, it's too late.