Hello Cynthia,

Yes, Japanese beetles can be quite detrimental to a lot of different plants and while they do not typically kill the plant, they can skeletonize the leaves in short order and leave it looking quite unsightly.  Some years the beetles are out in greater numbers than others so it can be an up and down cycle.  The beetles emerge from white grubs that are typically in your landscape turf, so controlling the grubs is how we manage Japanese beetles. This can take a number of years to get under control with repeated applications of insecticides that specifically kill the hatching grubs and applications must be timed properly.

Leaving a bucket of soapy water out will not do anything. But oh how I wish it would!  Rather you must hand pick the beetles off your plants and toss then into the soapy water to kill them.  They are slow moving so this is quite easy to do once you get over the 'gross' factor.  

Some people advocate for using Japanese beetle traps which attract the bugs with pheromones, but this is not recommended because you will be calling the party to every beetle in the neighborhood, thereby increasing your unwanted visitors. 

I m teaching an article from MSU which gives information on the insecticides you can use, if desired.  But, in all reality, I personally just drown them in soapy water.  You can also try spraying your affected plants with insecticidal soap. 

https://www.canr.msu.edu/ipm/diseases/japanese_beetle

Thank you for your question,

Kathleen