Answer: To keep 'Knock Outs' compact, take them down to about one foot every February. You can either shear everything down with power clippers or take the nice approach and use hand pruners to thin out some of the older canes and then shorten the remaining branches to just above outward-facing buds. You can also size-control 'Knock Outs' by shearing or pruning them back by about a third after the first main flush of blooms is done in June.
Japanese Beetles can be controlled with Diazinon or Sevin. Either of these pesticide sprays will take down the adults. Be sure to follow the label directions EXACTLY and use care when spraying ANY poisons.
Rotenone and Pyrethrum sprays are also effective. While these are made from plant sources and more environmentally-friendly, they are still poisons and should also be used with care. Neem oil has also been suggested, though with varying success reported.
Whichever one you choose, the sprays must contact the insect to be effective.
Or, you can embrace the classic pick-and-squish-or-stomp method. It works, especially with small infestations on specific plants. Some gardeners knock the slow-flying insects into containers of soapy water with a little oil floated on top.
Good luck with your roses.
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