weeping cherry tree

[flowerpower]

I have a weeping cherry tree. It has beautiful pink blooms on it every spring but they don't last long. The problem is Japanese Beetles around July. They eat almost all the leaves off the tree and the remainder of the year, it's kind of an eyesore. I've tried the traps but they seem to attrack more than capture. Is there anything I can spray on the tree that would be effective in repelling these pest? A friend told me to use dish soap. I tried, but when it would rain, the soap would wash off. The tree is about 18' high and it's difficult to spray every leaf. Can anyone help my poor tree?
Thank you