Warning, the diatomaceous earth would probably kill any bug that it comes into contact with, good or bad.
What some do is plant a rose bush at the beginning of the row. Its preferred by the Japanese beetles so when you see them gather there, hit the rose with pesticide and spare your hops.
What worked at my first property was skunks. They grub up my entire lawn and ate the beetles when they were in their larval stage. Supposedly moles and similar critters would work as well but when you are done with the beetles, you have to deal with the skunks.
Look up milky spore powder. It gives them milky spore disease. Supposedly natural but you have to treat a large area to get rid of all the beetles.
At our second place, my wife used an ice cream pail 1/2 filled with soapy water and a little shovel to flick them in. It took a whole summer but between the milky spore and soapy water, she got rid of them all...until the next summer when the larva in the neighbors lawn that didn't do a dang thing hatched and invaded. Eventually, the roses and cherry tree were dug up and only Japanese beetle resistant plants were put in.
In other words, your screwed. Don't do the traps, they just draw more in.
