Question
My roses in SW Oklahoma began losing leaves. The Yellow starts at the tips of the leaves in a 'V' and spreads downward in the leaf with brown following. It finally consumes the leaf.
This is happening especially with Mr. Lincoln, Tiffany and Gypsy and Chris Nuch.

The leaves do not match any photos in any of the rose books that I have.

We have recently gone into high summer temperatures (100 - 110) I now suspect that this may be due to heat stress, but can find nothing to compare the leaves.

I do spray the plants with systemic insecticide and systemic fungicide and tend to rule-out those problems.

Automatic sprinkler is set for mornings to prevent sun problems.

Any ideas what is the problem? and
What should I do about it?

Answer
As you have said, high heat will cause roses to go under stressful conditions. When they do they get rid of their leaves first, as the roots have semi shut down and can't support too many of them. Something else that is not a wise idea is to use any spray on roses when the temperatures are high. This is causing the brown on the leaves as well as sprays will only burn when it is hot. Also fertilizing isn't a good idea also as this will also cause problems with high heat as it burns. There is really nothing wrong with your roses they are just re-acting to the sprays you used on them plus the high heat. Once the temperatures are cooler, the roses will return to normal growth patterns. I would water but using a hose for a few days on them. Washing the whole plant well because the green leaves can still take up the water even though the roots have shut down. Watering in the sun does not cause burn on rose leaves that is a rose myth that has been debunked by commercial growers who water their roses in full sun.