If Japanese beetle infestations are light, the safest and most inexpensive route to killing the beetles is to pick them off the plants by hand and drop them into a bucket of soapy water.
A number of pesticides are available against Japanese beetles. Some ingredients to look for on pesticide packaging include carbaryl, acephate, and permethrin.
Organic, neem-based pesticides can also provide good control, as can insecticidal soaps. Note: Insecticidal soaps will kill the beetles, but don't provide any ongoing protection to your plants.
While it's the adult Japanese beetles that cause the most damage, their larval form -- grubs -- can also cause lawn problems. If your lawn has a grub infestation, treating for the grubs will kill most of them before they can emerge as adult beetles.
A number of grub-killing products are quite effective. There are also organic options including beneficial nematodes.
The beetles release chemicals called pheromones into the air. These pheromones attract other beetles. So if you see a few of the bugs, they'll probably attract more. Get rid of Japanese beetles early, before they can invite more of their friends to feed on your plants.
University research indicates that using Japanese beetle traps can actually make problems worse. The traps are intended to trap and kill the beetles in your yard. However, they use pheromones to attract the beetles to the traps. And these pheromones bring more beetles into your yard than the traps can catch.
Japanese beetles tend to be most active when temperatures are over 85 degrees Fahrenheit and the air is relatively still. Be especially watchful for new beetles coming into your yard during these conditions.
While Japanese beetles eat hundreds of different plants, they do tend to avoid: