White grubs are immature scarab beetles. Grubs live in the soil and eat the roots of plants such as grass. An adult female Japanese beetle can lay up to 60 eggs during the late summer. According to Michelle Niedermeier, coordinator of Integrated Pest Management (IPM) at Penn State University, a biological approach may be the best method for eradicating white grubs. While the biological method may take up to two seasons to be thoroughly effective, it may be a better alternative than spraying harmful insecticides that can run off into aquatic areas.
Sample the area of grass or lawn that may be showing signs of stress. Stress areas may be small patches of yellow or brown areas in the lawn. Remove a core of the soil just below the ground level. Count the amount of grubs you find. According to Niedermeier, if you find less than five grubs, chances are there is nothing to worry about. Finding a higher count may require a form of treatment.
Treat the affected lawn in late summer with a biological approach. Apply the treatment of Milky Spore Disease as directed to the lawn. The spore is non toxic and will grow in numbers after it has infected the grubs and kills them. The spores may take up to two full seasons to be fully effective, but may eliminate the grubs permanently from the lawn.
Spray beneficial nematodes to the affected areas in the fall. Nematodes are small microscopic worms which actively seek out and invade the grubs. The nematodes release a bacterium which kills the grubs. Mix the solution according to label directions. Use only a clean sprayer that does not harbor any residue from insecticides, as the residual chemical will kill the beneficial nematodes.
Apply a biological insecticide called neem oil. Neem oil comes from a tree and can act as a deterrent to egg laying insects. Follow all label directions when applying to the lawn.
Spread a chemical insecticide if the infestation is just too great for you to control biologically. Follow all label directions in the application rate and process.
Reseed the damage areas with the same grass species that is already present in the lawn. Water the seed well into the soil using a garden hose and sprinkler attachment.
Mow the lawn keeping the length of grass between 2 inches to 3 inches in height. Never remove more than 1/3 the height of the grass blade at any mowing. Removing more than this amount may cause stress on the grass, creating the opportunity for a grub worm attack.