Some chemicals used to kill Japanese beetles are carbaryl, acephate and permethrin. Carbaryl affects the insects' nervous system. It effectively kills Japanese beetles but also destroys beneficial insect populations. Acephate also targets the insects' nervous system; however, acephate is a potential carcinogen. Exposure to this chemical also produces symptoms such as vomiting, nausea and disorientation in animals and humans. Permethrin is used as an insecticide against disease-carrying insects and to combat scabies in humans.
To avoid the side effects of chemical pesticides, use alternative solutions such as hand-picking, nematodes, milky spore and neem oil.
Hand-pick adult Japanese beetles and drop them in soapy water. Complement this by applying milky spore powder on the ground between late July and early August. Beetle grubs ingest the powder, which contains bacteria that multiply and kill the grubs. New grubs ingest the bacteria released by decaying grubs into the soil, providing continuous protection against Japanese beetles.
Nematodes are parasitic worms that operate similar to milky spore. They inject bacteria into the grubs, which serves as food for the nematode and results in the grubs' death.
Neem oil repels Japanese beetles and protects plants from fungi and black spot.
Shrubs and trees such as boxwood, lilac, red maple and magnolia naturally repel Japanese beetles. Plant them around affected areas to limit the beetles' food source and keep them away from the garden.