Holes in the leaves of knockout roses,
What causes the holes and what can I do about them?
Certified GKH Gardening Expert
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.