The grubs resume feeding once the ground warms in the spring and pupate in late May or early June. The adults begin emerging about three weeks later. Damage The green June beetle grub differs from other white grubs in their feeding behavior. Damage to turf occurs as a result of their unusual habit of tunneling as well as root feeding. This activity begins in early to mid-August when the disturbed grass may wilt or die if conditions are dry.
Damage is minimal when grub density is low or if the grass receives plenty of moisture.
As the grubs grow, tunnels become vertical and deeper with turf damage becoming more severe. Tunnels to the surface are kept open by grubs pushing little mounds of loose soil to the surface. The resulting mounds appear similar to earthworm castings. To determine that a mound was made by a green June beetle grub, wipe the mound away and feel for a hole in the ground about as wide as your finger. Earthworm holes rarely exceed the diameter of a pencil.