I tried Neem Oil with moderate success, but it needs frequent reapplication (especially after rain). Eventually my J-Beetle problem resolved itself after I started treating treating my lawn for grubs (non-organically).Have you tried milky spore?
I am going to apply the beneficial nematode Heterorhabditis bacteriophora in my hop yard, gardens, and around the ornamental trees that Japanese beetles love in September. Heterorhabditis bacteriophora is a hunter-killer nematode that is supposed to be effective against Japanese beetle larvae. I used beneficial nematodes to take care of a massive flea infestation that I had in my yard at my prior residence. The nematodes made quick work of the flea larvae in the soil, putting an end to the life cycle. The problem never came back.
With that said, Japanese beetles are not fleas. The Japanese beetles in my area have been subjected to pesticides long enough that they are difficult to kill. PyGanic is supposed to be an effective contact killer. However, it appears to be ineffective against the Japanese beetles in my area. I personally witnessed Japanese beetles survive for hours after direct application. I do not know if PyGanic eventually killed the beetles because the leaf on which they were feeding was skeletonized by the next morning.
The main problem I am up against is that I live in a semi-rural area where the farmers practice no-till farming. No-till farming is good for the soil and Japanese beetles.
makes sense. June bugs are the adult for of the lawn grub. Get rid of the grubs and you thin the June bug herd (your neighbors have help to eliminate them) and get the moles to stop digging up your yard too. Moles eat the grubs.