Another great trap crop for Japanese beetles is grapevine or wild grape. I have wild grape that grows as a weed and the JB's love it and stay there.
Milky spore can be purchased as a powder you put on your lawn, which is often where the grubs are. It is applied in spring, infects the grubs, so they don't emerge to become JB's. But it only works on the JB's, not other kinds of beetles, not even June bugs or other things with similar white grubs, so you do need to know what you have.