Question
The uppper leaves on my knockout rose bush in a patio planter have gotten thin and tiny lacey holes have appeared on the leaves...........
I do not see any evidence of spider mites.........
How would I treat the bush?

Answer
Lacey leaves are caused by a rose slug. They work under the leaves and suck out the nutrients until the leaf finally dies.  Check and see if you can find what looks like a tiny dark brown slug. If you find even one then that is what is causing the problem. Any rose insecticide will solve the problem for you. If there is no signs of an insect doing the damage then it can also be caused by fertilizer burn or even a spray burn. What ever the cause is the leaves will renew themselves as roses can put out three sets of leaves.