Help-what starts off as a perfect rose when it opens suddenly wilts?

Could this be a soil problem? I put in a new bed last year and as I dug it up there were a million ants in there, I treated the area with ant killer, then added new soil and sand (the area was all clay). I put in two new tea roses and they looked healty until the flowers began to open and then they just stopped blooming and wilted. This year I added a new tea rose to the area and the same thing is now happening with the new rose. The leaves look fine but once the rose begins to open it just wilts over. I know teas are more difficult, but I've never had this happen before. Any ideas? I'm really wondering if it was the ant killer : ( Thanks.