I second RichZ with using the Japanese beetle traps. Some people say that they attract more beetles to your yard, and that might be true, but in my experience they work a treat. Unfortunately, you won't get rid of the grubs that way. Grubs are usually fairly close to the surface of the soil this time of year. Dig them up and throw them to the chickens. The issue with nematodes is that you often have to add them for more than one season in order for it to be effective.