We'll need a lot more info before we can even make a guess, and photos of both the dead and "dying" would help immensely. At the very least we'll need details:
Did the leaves have spots/dry edges/mottling/yellowing/distorted shape?
Did it occur suddenly, all at once, or did symptoms creep up?
Are the canes otherwise healthy on the ones still alive? Did you notice discoloration/spots on the canes of the ones that died?
Just how hot has it been, and for how long?
Has it also been dry? If so, have the roses received supplemental water?
Are these new, or established roses?
Have you sprayed any chemicals recently? That includes insecticides, fungicides and heaven forbid, herbicides (roses are VERY sensitive to even minor drift of RoundUp, for instance). Are you in farm country where chemicals are regularly sprayed on crops?
Are the roses firmly rooted, or can you easily move them, or even pull them up without much effort? (varmints eat roots)
Did it start with one rose, and move to the next nearest, or was the appearance of symptoms random?
I think you get the idea. But right now, all we have to go one is the equivalent of, "Doc, I have a fever", lol. You might have any one of 10,000 diseases, but he'll need a lot more information before he makes a diagnosis ;)
John
