What is the best way to kill Japanese beetles from eating your plants?

Spread milky spore on your lawn...it well spread and get rid of jb grubs over time. Apply spring and fall.

You can put traps way away from your garden-i instead fill a jar with vinegar and pick and pinch them. It's a full on war.

Spray Neem Oil, organically acceptable, and reasonably priced! It doesn't outright kill them but makes them forget to eat and breed. You will notice them slowing down in a couple of days. Safe to use on all plants (but avoid applying on a sunny day) with no withdrawal time between application and harvest of most fruits and vegetables. Neem oil works on about any bug that eats your leaves. It is worth your time to 'Google' Neem Oil.