The most important thing to understand about Japanese beetles is their feeding doesn’t kill trees, shrubs and flowers. Granted, it isn’t fun to see the lacy leaves they’ve created, but pesticide management options require thought and planning before you set out for revenge.
Systemic insecticides, for instance those containing the active ingredient imidacloprid, are taken in by plant tissues. Systemics may have a label for application to trees and shrubs but before these are used, the applicator should make sure the plant is past its flowering stage in order to protect pollinators. Also, a systemic product can never be used on linden trees.
Topical insecticides with the active ingredient bifenthrin or carbaryl are those that coat plant tissues so Japanese beetles ingest the toxin when they eat. As you would guess, topical insecticides can wash off in a rainstorm, so using a product called a spreader sticker will help. Again, it’s important that topical insecticides are not sprayed on flowers in order to keep pollinators like bees and butterflies healthy.
Remember that Japanese beetle traps are too good at what they do—attracting Japanese beetles. Research indicates there is more Japanese beetle damage in yards with traps than those without. While Japanese beetles are accomplished at eating, they are uncoordinated at flying. Any beetles that bumble past the traps will be diverted to nearby plants where they begin feeding.
Japanese beetles love fruit, so keeping them away from your prized peaches is a problem. There are fruit bags, made of fabric, mesh or nylon, that individually protect fruits from any bug onslaught. Kaolin clays can also be sprayed on fruits and act as deterrents to insect feeding.
Where practical, picking Japanese beetles off plants is very effective and doesn’t cause harm to pollinators. The best time of day to do this is at 7:00 in the evening. Instinctively, Japanese beetles drop when the plant they are on is disturbed. You can use this instinct to your advantage by holding a small bucket of soapy water beneath a branch, giving it a light tap and watching as the beetles drop into the bucket. Satisfaction and clean-up in one step!
More information can be found here: https://extension.unl.edu/statewide/douglas-sarpy/pdfs/ce/resources/ce-dealing-with-japanese-beetle.pdf .