Answer: I know the beetles are awful, some years they are worse than others, and of course they do prefer certain plants. However I would never recommend using a soap -- especially the modern dish soaps which are usually detergent plus additives -- on a Japanese maple, their foliage is very sensitive. Also, the soaps are a contact control and have no preventive effect. Instead you could try controlling them at the grub stage using milky spore disease or beneficicial nematodes on your lawn areas, or you might consider using the pheromone traps if you have a very large property and can locate the traps at a far distance from your affected plants. (Located too close they have the opposite effect and attract them.) Another option is to repel them using a spray containing neem oil, be sure to read and follow all of the label directions and spray when the air is calm -- you could also consider wearing protective glasses and a mask. You can also try shaking them off the plants and dropping them into soapy water, they tend to be most sluggish early and late in the day. I'm sorry there is no magic answer for this pest.
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