My knockout roses have some yellow leaves and I am not sure if I am over watering them.
Yellow Leaves on Knockout Roses
If the yellow leaves are towards the bottom of the bushes or are close in to the center, it is normal. The bushes other foliage tends to shadow those leaves and thus the bush really does not need them and lets them die back. If there are dogs in your area, they could be doing their pee business on them too. I have had that happen to some of mine and lost all the leaves on one side of the bushes!! Washed the area down and kept it watered well plus put some dog deterant around and the foliage did return.