Lawn grubs, the 1/2-inch-long larvae of the Japanese beetle, feed on the roots of your lawn. Typically, beetle grubs can be found about 1 to 2 inches below your turf. Small numbers of grubs do not cause significant damage, but as populations grow, your lawn can suffer damage. As the grubs eat the roots, the plants begin to lose contact with the soil. Moisture uptake is compromised and the sections of turf may pull away like a carpet.
Obtain milky spore powder from a garden center, nursery or online retailer. Bacillus popilliae is a bacteria that causes disease in Japanese beetle larvae. It is harmless to people, pets and wildlife. According to Cornell University, the "Japanese beetle is the exclusive host of the strain of B. popilliae."
Apply milky spore when soil temperatures are above 70 degrees Fahrenheit. The University of Connecticut advises, "the disease-causing bacteria develop best at soil temperatures between 60 and 97 F."
Consider beneficial nematodes to control lawn grubs. Heterorhabditis bacteriophora nematodes are tiny, unsegmented worms that attack and kill grubs. These grub-killing nematodes are sometimes called Hb nematodes and are available from specialty retailers.
Use Hb nematodes in warmer weather, when the soil temperature is at least 68 degrees Fahrenheit.
Apply Hb nematodes in the late afternoon or early evening when soil temperatures. The soil should be slightly moist before application and the product should be watered in immediately. Apply water to your lawn after applying Hb nematodes.