Hand Pick: Unfortunately, the most effective way of getting rid of Japanese beetles is to hand pick them. It's time consuming, but it works, especially if you are diligent. When you pick them off, put them in a solution of 1 tablespoon of liquid dishwashing detergent and water, which will cause them to drown.

Beneficial nematodes kill the grubs that turn into Japanese beetles. Ideally, apply them in spring before the beetles emerge. The second half of this 1-2 prevention punch is Milky Spore, which also kills grubs. It takes a year or so to get established in your soil, but it keeps working for 10 years or more.