I do not have Japanese Beetles here, but I do have a close relative that is just as destructive. Chinese Rose Beetle. The control is the same. Do not depend on Sevin or pyrethroids for control. Use a soil application of imidacloprid. When Merit first became available in the 1990's, my first test was on my rose garden. It worked so well that it became a standard for control. Once I stopped having to constantly spray Sevin, Diazinon, or Malathion for control of these pests, the health of the roses improved dramatically.