You'll get some better answers here before long, but don't forget the county extension of your state's land grant university. They'll have authoritative info on all subjects horticultural as they pertain to your locale.
Sevin dust.
I use Talstar One. It kills everything.
Nematodes kill darn near every vegetable we put in the ground.
Yes. Works very well, but it is not a quick fix. It took me about two years before those critters were gone. Got rid of the moles as well, when their food sourse was gone.
If you don’t want to use chemicals,
look into “diatomaceous earth”.
Kills anything with an exoskeleton.
Excellent results. Will definitely use again.
Try putting up a picture of Helen Thomas. That would keep anything away.
I have 2 Hives of Honey Bees(anyone want Honey this year ;-)) and cannot use ANY Chemicals on my land. So I am Looking to Lady Bugs, Milky Spore and Nemetodes to do the trick. Japanese Beetles ATE my Garden Last year AND My POOR Doggys were in FLEA agony!
I garden the way my grandparents did, which was organic because you used what was available on the farm. I find liquid soap (not detergent) spread on leaves, sometimes, you might have to dip the leaves in the suds, works wonders for a bunch of nasty critters, including aphids.
I also plant extra for the birds, encourage swallows to build nests.
Sevin does work. Nemotodes are dangerous, will eat everything.
Then there’s paying the neighborhood kids a nickel per beetle, which works until they get old enough to say “that’s SO GROSS!”
This year I'm planning to try Milky Spore. I know it's a multi-year proposition.
I don’t think I’ve seen a Japanese Beetle around here in years. We were absolutely overrun with them in the 80’s. Something in nature has obviously adjusted and is controlling their population numbers.
Never used it; we spritz with diesel. It kills practically any and all pests and quite efficiently.
The milky spore takes time to take effect and it does prove effective, however, my poor plum tree immediately succumbed to a severe black knot infection.
Don't know if the beetles had anything to do with the black knot, but I miss the annual harvest of tart plums which I used for hungarian plum dumplings (Szilvás Gombóc) .
For consideration for the gardening ping list.
Milky spore works better in warmer climes. It is virtually useless in the northern tier. Nematodes would likely work most anywhere.
I live in the North. I use a mason jar containing a couple inches of water and a few drops of detergent to catch the beetles I knock off the leaves. The detergent reduces the surface tension so the beetles sink. The practice seems to keep the population at manageable numbers. Hope this helps. sd
I tried a napalm airstrike once. Not recommended.
Last summer I tried a mix of dish soup, water, and hot sauce in a spray bottle. I was pleased with the results.