The jap beetle traps do work, it's all about placement. If possible, try to place them about 20 feet beyond your property line, or 50-100 feet from your crops. I use 3 traps on three corners of the property where I work and grow my hops. I saw a marked reduction in the number of beetles on my plants after the first day of having the traps up. I probably collected over 20# of beetles in the past 2 weeks. Not trying to say that they are a miracle cure, but the traps aren't as bad as previous posters claim. Ideally, if your a real stinker, you could buy about ten and then give them to all your neighbors.
I haven't had any success using insecticidal soaps on Jap Beetles. Their hard body just seems too resistant, but YRMV. One chemical that has worked well for me is SEVIN. It's not labeled specifically for hops (not that anything is) but it is safe on fruits and vegetables as long as you adhere to the specifications on pre-harvest spraying.
You can try the various essential oil sprays or neem oil, although I haven't had much luck with those.
As most have mentioned, Milky Spore is the best control, however it takes a year or two to become effective. The best time to treat your lawn is in the fall or early spring, when the grubs are present.
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