No leaves left!

I have had problems with some half-standard flower carpet roses just recently. They were planted in the ground but all of a sudden nearly all the leaves dropped off leaving me with stems and a few leaves at the top.

There was no sign of insect damage so I took them up to inspect the roots incase something was nibbling away at them but I found nothing wrong.

I am puzzled because a few have gone and others that were next to the diseased looking ones are all doing fine. They are now potted up behind the shed. Any ideas anyone?

 

Did the leaves get black spots on them, then turn yellow or brown.
If so it's almost certainly black spot, you need to collect all the leaves which have dropped of and get rid of them, (not in your compost heap/bin)
I spray mine with Rose Clear, supposed to do it fortnightly from April, I often forget to start in April, so I still have it.
Some varieties are resistant to it, some more than others.
It can overwinter in diseased leaves which drop from the plant..