Grubs are a notorious pest in lawns. They eat the grass roots below the surface of the soil, leaving behind patches of dead grass. When the term "grub" is used, it is usually referring to larvae of three types of beetles, the Japanese, the june and the European chafer. The remedy for removing them is the same for all of them and according to Michelle Niedermeier, of Penn State University, you "should try using an integrated pest management (IPM) approach. 'IPM "integrates" many management tactics for more effective pest management results.'" Their life cycle starts around May when the beetles come out of the ground, mate and then lay their eggs under the soil. These eggs quickly develop into the larvae that are called grubs and feed on the roots of the lawns. They continue to grow for the next two years until they emerge as adult beetles.
Check that the problem is from grubs by digging up a 12-square-inch section of lawn and counting the grubs you find just under the lawn. If you have more than five in that section, you should treat the lawn. If you have fewer, a whole-lawn treatment is probably not necessary.
Apply milky spore powder over your lawn in late summer or early fall. It is important to apply it while the soil is still warm and when the grubs are still close to the surface, feeding on the grass roots. The grubs will eat the powder and die, releasing thousands of spores into the soil, ready for the next generation of grubs. This remedy takes a few seasons before it is effective, but the powder is readily available at garden supply stores.
Use beneficial nematodes. These microscopic worms will feed on the grubs and kill them by bacterial infection. Because you apply the nematodes while they are alive, you will need to use them immediately after you have purchased them. You can usually find them at garden supply stores or nurseries.
Keep your lawn in good health. A healthy lawn will be able to resist grubs eating a few of its roots with new growth. Keep it watered and fertilized. Do not cut it so low that you stress the lawn in hot weather.
Reduce all visible beetles by removing them by hand from roses and fruit trees. Drop them into a bucket of soapy water, and they will sink to the bottom and die. Hang yellow beetle traps from fruit trees. These measures will reduce the number of beetles that might lay eggs in your lawn. Used on their own, they will probably not be enough to conquer the beetle problem, because the beetles can fly in from neighbor's yards. You should see a drastic reduction in the number of grubs by using a combination of all these treatments.