Judging from many inquiries that I have had, I have escaped the main onslaught of Japanese beetles. This is my second year of good fortune.
As many of you know, I plopped a house in the middle of a weed jungle about 14 years ago. As I slowly win the battle with weeds I have eliminated an infestation of smartweed that was a prime attractant for the beetles. Perhaps one control thought is to eliminate some of the plants that are their favorites.
If your infestation is light, soapy water may be the solution. Pick or shake them into a bucket of soapy water. They don't like that. The trick on many insects is to clog their breathing pores. You can also use a spray bottle of soapy water successfully if you get good coverage.
You can buy an insecticidal soap or you can make your own with a few drops of dishwasher soap mixed with water.
Digressing a bit, I suspect that soon some of your spring hanging baskets may be getting difficult to keep moist, The same mix of water and dishwasher soap will revitalize the moisture holding characteristics of soil in your basket.
The next line of attack on the beetles is to spray. The literature suggests for those who want to go all-natural to use a pyrethrum. This is a chemical derived from natural plant sources and is very effective. It's easy to find, too.
This troubles me just a bit since all chemicals are rated according to toxicity with something called LD 50.The LD stands for lethal dose. The lower the LD number, the more toxic. Don't get too alarmed. Even table salt has a rather low LD number.
My problem is that many of the synthetic materials that will be very effective on the beetle have much higher LD numbers than the pyrethrums. In other words, they are less toxic.
Common synthetic insecticides that work well are Sevin, Malathion and Orthene. I like the middle one since it targets beetles and is rather gentle on our insect friends. One of the keys to general insect control is to maintain a balance of good and bad insects.
Sevin provides a quick kill on beetles but is also more harmful to beneficial insects. Spraying with Sevin is like providing a banquet for the little red spider mites because it also kills several beetles that feast on spider mites.
There is also at least one bacterial product; it's called milky spore and can be spread to target the beetle grubs in the soil. In other words, you can solve the problem of Japanese beetles before you see them.