You also have to take care of the Japanese beetle grubs in the soil or you'll be right back where you are next year.
I've had good results using milky spore. Just about due for another application after... hmmm... guess it's been a good five years. The first couple of years, the spore multiplies in the ground, killing off more and more of the grubs. (And they are some UGLY looking bugs!)
I doubt they'll ever be eradicated, but you can control them.