Holes in the leaves of knockout roses,
What causes the holes and what can I do about them?
The holes in the leaves are likely due to little beetles that have long snouts. They poke into the leaves and suck out the juices. I would recommend buying some Bayer Tree and Shrub granules. Apply the granules per the label instructions for ornamentals/shrubs. The granules have some food in them to help strengthen the rosebushes and also a systemic that will kill the beetles and some other insects or worms that would suck the juices out of the leaves. You could also use a systemic insecticidal spray if you wish to accomplish relief from the problem.