Establish Natural Defenses
Over the long term, a good Japanese beetle defense involves improving the soil in your yard so that the beneficial organisms that live in the organic matter there are active and numerous. They prey on Japanese beetle eggs under the grass in around plant roots. Mulching is the easiest way to add organic matter to the soil. As it slowly breaks down with the help of earthworms soil is able to hold air and moisture better which makes its beneficial microlife happy and industrious.
Spread 2 to 4 inches of some organic material such as chopped leaves, grass clippings, compost, hay, shredded paper, or straw over bare soil in and around shrubs, flowers and vegetables. Topdress lawns with topsoil, compost or peat moss, or mulch them with shredded leaves as you mow with a mulching lawnmower in the fall. This will add organic matter and improve the soil over the entire yard.
Besides building rich soil, it is a good idea to encourage the many insects and animals that normally prey on insect pests to reside in your yard. Natural predators of pest insects come in all shapes and sizes. While many are insects themselves, others are microscopic organisms that attack eggs in the soil or amphibians or birds that eat adult beetles. The more of these different kinds of predators that live in your yard, the fewer pest insect problems you will have. They will take up residence in a yard that includes their favorite plants and other foods. The greater the variety of plants on your property, the greater the diversity of natural enemies of pest insects that will reside there.
Attract Beneficial Insects to the Yard
Birds, spiders, and predator insects kill many more Japanese beetles than a homeowner armed with insecticide ever will. If you don't use broad-spectrum insecticides, there should be lots of beneficial insects living in your yard. Spiders and ants will consume large numbers of beetle eggs in the soil even before they hatch. Spined soldier bugs, ground beetles, wheel bugs, and the larvae of tachinid flies attack the grubs in the soil. Boost resident populations of beneficials by ordering some additional ones from mail order suppliers. Properly introduced into the yard, they will search out and feed on the beetles and other pests as well.
Encourage all natural predators of Japanese beetles to stay in your yard by providing them with a tempting variety of their favorite plant sources of pollen and nectar. One way is to plant a patch or border of their favorite type of flowers. Border Patrolä, a wildflower seed mix contains seed for plants that are particularly attractive to beneficial insects.
Feed Birds Year Round
Next to beneficial insects, songbirds consume the most pest insects in your yard. Grackles, meadowlarks, crows, catbirds, cardinals, blackbirds, robins, and starlings eat lots of grubs as they move to the surface of the soil prior to emerging as beetles. Starlings, robins, catbirds, and purple martins, blue jays, and cardinals eat adult beetles.
Mow The Lawn Properly
Japanese beetles prefer to lay their eggs in turf grass that is short. They do not like grass that is more than 2 inches high. Furthermore, tall grass harbors ground spiders and ants that prey on beetle eggs. Most lawn grass grows best when mowed tall anyway, so mow your lawn no shorter than 2 inches to effectively reduce the number of white grubs and home grown beetles next year. Click here for more information on Mowing Lawns.