NO, NO, NO!!!! I've gone this route and I never had so many Japanese beetles on my garden!!
Beyond the satisfaction of capturing hundreds of beetles in a trap, does your yard or garden actually benefit? The answer is, most likely, no.
extension.umn.edu
You end up getting ALL OF YOUR NEIGHBOR'S beetles feasting at Your house.
Dunno about any other pheramone traps...
All of the rest of your advice, @Zeedman, is Sound.
My experience has been more favorable. Trap placement is important; I initially moved the traps several times, until I found the locations that were most effective. One of those locations is hanging from a spruce tree, something they won't feed on. Yes, I do catch hundreds each day - but I see no indication that the traps are increasing the numbers in the gardens. To the contrary, for the most part, only a few make it to my gardens. Those "scouts" send out pheromones which would attract the swarms, so I go out 1-2 times a day with the spray bottle to discourage that.
Oh, and what to do with those hundreds? I empty the seething mass of beetles into a bucket of soapy water, swish them around enough for all beetles on the "raft" to be wetted down, and dump the bucket when all are dead.
DO NOT dump the beetles anywhere near the garden (where the smell will attract more) or anywhere upwind -
the putred smell is horrible, intense, and amazingly long lasting. I can dump wasp nests or piles of dormant carpenter ants (from splitting wood) and birds or animals will eat them... but apparently, nothing eats dead JB. The pile of JP I dumped in the gravel driveway last year was still there after the Spring thaw. Dump them in a sewer if you have one.
Adult Japanese beetle damage usually affects only the appearance of plants.
Healthy, mature trees and shrubs can tolerate a lot of feeding without significant, long-term injury.
Young or unhealthy plants may be stunted, injured or even killed from severe, persistent feeding.
This is why I moved my young grapes onto the porch.
Sorry, but that is not the case here. Since they first moved into this area 5-6 years ago, their numbers have been growing exponentially. There are hundreds feeding in my trees! Besides the wild grapes (which they will strip down to the leaf veins) JB have a few plants they are especially attracted to - and those they will damage severely. Soybeans are one of those; they would swarm on & destroy my soybeans if I took no measures to prevent them from doing so. Some pole beans too, although they will show no interest in other varieties nearby. Unfortunately the JB really like Fortex, they attacked the vines so heavily last year that we only picked a few hands full, and froze nothing.
Jembo Polish nearby was virtually untouched. This year I am growing Emerite as my pole snap bean, because they have historically been less interested in it.
They completely ignore limas and yardlong beans though, and seldom attack bush beans. Surprisingly, their only interest in runner beans seems to be their blossoms (and okra blossoms too).
Zebrina mallow makes a good trap crop, because it is a plant they prefer. I've always allowed a few of those to grow along the fences, or in open spots where they are out of the way. The beetles seem to stop on the mallow on their way in; I can walk along the outside of the fence line with my spray bottle & pick them off.
But I have to acknowledge that if the population continues to increase, all of the preventive measures I'm using may eventually become ineffective. I dread turning to a lawn service, but at some point treatment to kill the grubs may become necessary.
