Kate,

Japanese beetles are a real problem this year. I recommend you take a look at this brochure the US Ag Departemtn which I think you will find useful: https://www.aphis.usda.gov/sites/default/files/JBhandbook.pdf

One of the key take-aways from the brochure is the utility of early intervention and prevention. That said, right now there are several things possible to ameliorate the situation:

1. Pyrethrin spray

2. Pick them off and drop them in a container/bucket of soapy water. (This may seem laborious but it does work and it's easier than it sounds.)

3. Japanese beetle traps available at many garden centers and online. Japanese beetle traps use lures to attract beetles with scents and pheromones. The beetles use their antennae to pick up the scent and are drawn to the trap. Once inside, the beetles release more pheromones that attract even more beetles. The traps are designed to catch the beetles in an attached bag where they eventually die on their own. Traps should be placed about 4 feet off the ground and about 30 feet away from the planted area (otherwise you are attracting beetles to the plants themselves). If you can determine from what direction the beetles are coming, place the traps there. Empty daily if possible.

And good luck. They are ravenous critters. 

Richard

Master Gardener Volunteer