JAPANESE BEETLES

UH-OH! We've just discovered several Japanese Beetles - two (on top of each other) on the Rose of Sharon and one on of each of my rose bushes. I got a paper towel and squished these -- but how many more are lurking? I've got some Sevin Bug Spray - ready to attack. And I'm researching online just what I can do - I know they can get out of control and I figure I better take the offense! Anybody have this problem?