Question
I live around Atlanta Ga, I have several knockout roses that are "shedding" leaves.  The leaves are turning yellowish-brown before falling off.  I have one that is virtually bare, yet still blooming.  Any ideas on what could be going on? I have a sprinkler system that provides adequate coverage and they get at least 4 hrs of sunlight per day.  

Answer
When a rose drops it leaves it does so when it is under stress. If the leaves didn't have any fungal disease on them such as black spot, then it could be the following problems.
Temperatures higher than normal and so not enough water getting down to the feeder roots.
The rose was planted from a pot that had a lot of perilite. This material acts like a blotter but has to have extra water or it dries out the deeper roots.
However your description is what happens when there is a lack of enough water and the rose starts to save itself.
To prove just how far the water is getting down just take a trowel and dig down near the base. It should be damp to at least 6 inches. Roses need 5 gallons of water every 5 days under normal conditions. This is about a bucket full of water. Also, any type of mulch is a good idea as roses love cool, damp roots. Hope this helps.