Easiest way to get rid of japanese beetles?

Go out early morning while they're sluggish and knock them into a bucket of soapy water. Sounds tedious, but it's the cheapest thing that works. Skip the pheromone bag traps - they pull in beetles from the whole neighbourhood and plenty land on your plants instead of in the bag. Longer term, beneficial nematodes or milky spore in the lawn go after the grubs.