Check for white grub worms in late July and early August. Wet soil is favorable for grubs. Dry soil is bad for grubs. So do not irrigate more than necessary. At this time of year, the creamy white C-shaped grubs are about a half to one inch long and ready to turn into June beetles. These grubs have finished feeding. The eggs laid by this year’s June beetles turn into larvae which are large enough to do this type of damage in late July or early August.

Treatment is only justified you find 5 or grub worms per square foot in the grass areas of the landscape. Grub worm damage appears as irregular shaped areas of weakened, dying or dead grass. In severely damaged lawns, the dead grass will pull away like a piece of carpet because the grubs have eaten all the grass roots. If you suspect grub damage or if you have had grub damage in the past, check several locations in your lawn by digging samples about six inches across and four inches deep, deeper in sandy soils. If you find 5 or more grubs per square foot, treatment is justified.

White grubs damage lawns by eating the roots of the grass. The white grub is the larvae of the June beetle. But just because you have June beetles does not mean you will have grub worm damage. June beetles are attracted to lights in early evening and at night. Turn out the lights.

Treat with bio insecticides such as parasitic nematodes, Heterorhabtitis or Steinernema, or chemical insecticides such as imidacloprid (Merit), isofenphos (Oftanol), and isazophos (Triumph). If soil is dry, the treatment will not reach the grubs. Water about quarter inch the day before treatment and half to quarter inch after applying treatment.

Cost of treatment will depend on the size of the lawn area. A landscape professional can easier give a diagnosis and treatment estimate.