Can I cut back my knockout roses?
They were infested with Japanese beetles and their leaves are yellowish.
I would not prune the rosebushes back more than 4 to 5 inches at this point. They are probably very stressed out by the Japanese Beetles attacking them, they need to be kept watered well. I recommend watering them with some water that has a product called Super Thrive mixed into the water along with a little water soluble fertilizer, not as much as you might typically use but about half that amount on the fertilizer. This will help them deal with the shock and stress they are currently under. I would also recommend spraying the rosebushes with either Bayer Complete insecticide or Sevin to help lessen the Japanese Beetle problems.