Mow Tall Thick Turf
Japanese beetles do not like to lay their eggs in tall grass. If you maintain your lawn at 2.5 inches and overseed to get the turf thick you will go a long way to discourage any Japanese beetles laying their eggs in your lawn.
Improve Lawn’s Soil
The best way to eliminate grubs under the lawn is to improve the soil there so that natural predators such as ants and ground spiders thrive and eat the eggs and larvae. Create a rich environment for them by adding organic matter to the soil and aerating it to provide the air and nutrients they need. Topdress the lawn with organic material such as peat moss, compost, topsoil or a mulch of leaves shredded while mowing with a mulching mower. A bonus is grass roots that penetrate deeper and plants that are healthier and better able to withstand grub attacks.
Increase Plant Diversity
Grubs are normal citizens in a healthy landscape. They and the beetles have a role in your ecosystem. Having some grubs is not a problem. Having too many grubs in one place is the problem. An overpopulation of grubs is generally a sign that the natural predators in your yard are not able to keep after them and the beetle population has exploded
Bring In The Natural Predators
Encourage populations of the many predators living in your yard that normally control these pests by planting plants that they need for food and shelter. Besides the ants, spiders, and ground beetle predators of grubs are rodents, amphibians and birds, including, Robins, Cardinals, Blue Jays, Purple Martins, and grubby old Starlings. The greater the variety of trees, shrubs and decorative plants on your property, the better it can support a diversity of natural grub and beetle enemies.