Advance scout beetles mark territories as good feeding grounds for others to follow. Once marked, your garden will be considered a Japanese beetle buffet. To avoid being on the menu, catch and kill these first beetles and use them to repel any others that happen your way.
I wrote an article about making an easy homemade Japanese beetle repellent last season. You can read it at: Control Japanese Beetles Naturally
This method really does work for me, and I've gotten some great feedback from others about it too. What started me on a quest for a homemade solution was an article I read at Consumer Reports that gave a poor rating to conventional Japanese beetle traps.
A note before you head over to my article and recipe: It's critical that you catch the first Japanese beetle scouts before they have a chance to spread the word about your tasty garden. It may sound silly, but it's true. This is one instance where timing is everything.
If you're too late to catch the early scouts this year, there's still hope. If you keep killing every beetle you see, you'll be reducing the population that will deposit grubs on your property for next year; so even if this year's roses look a bit "lacy", next year you'll have fewer beetles to worry about.
Other things you might consider:
Next year put down a nematode preparation. Nematodes are microscopic, beneficial worms that kill Japanese beetle grubs before they come out of the ground. Milky spore works in a similar way. Nematodes and milky spore are safe and will help get your garden off to a good start next spring. So even though this year may seem hopeless, next year is bound to be better.
Employ plants Japanese beetles avoid. There are some plants these beetles steer clear of. They include: members of the garlic and onion family, catnip, tansy, peppermint and rue. All these herbs have strong, non-flowery fragrances. You may want to experiment with them and possibly others as well.
In some studies, Japanese beetles were repelled using essential oils, but the research is still ongoing. Cedar oil was particularly effective. (That may mean that even adding a little cedar mulch around your roses could be beneficial.)
Learn more about Japanese Beetle control methods with my updated post. There's a lot to learn and consider: What You Need to Know to Get Rid of Japanese Beetles