Japanese beetles can wreak havoc on your garden, eating straight through the leaves of plants, leaving only a skeleton. The females lay their eggs in the soil in the winter. These hatch in the spring and start eating the roots of the plant. The full-grown, 1/2-inch long beetles appear in the summer. Getting rid of these beetles entirely is impossible, so you must focus on a number of methods to control the population and save your plants.
Choose plants that do not have a problem with Japanese beetle infestation. Purdue University Extension includes a list of susceptible and resistant plants in its article "Japanese Beetles in the Urban Landscape." Resistant plants include red and silver maple, magnolia, flowering dogwood, common lilac, holly, red mulberry and shagbark hickory.
Monitor your plants throughout the spring, looking for the first beetles that appear. Mix some dishwasher soap in warm water until soapy. Pluck the Japanese beetles off the plants, preferably in the morning hours when the temperatures are cool and the beetles are sluggish, and drop them in the soapy water. This should control the population of beetles where you have smaller populations.
Apply an insecticide to the plants if the infestation is too large for hand-picking. Usually, if the beetles eat more than 15 percent of the foliage of a plant, insecticide use is warranted. Choose an insecticide with permethrin, carbaryl or malathion and follow the directions on the package for application instructions. In most cases you can use spot treatment, as many beetles usually reside on single plants.