Here at the Pulaski Co Extension office we have about 5 pink single Knockout roses and 5 double Knockouts planted. Last year I saw this problem and stupidly did not remove the plants. This year, the problem is here again!
This is called rose rosette virus. It is incurable and terminal. It's best to remove affected plants to protect others from getting the virus. It is transferred via mites.
Sorry plants, but y'all are outta our garden!