Answer: Roses do surprisingly well in Phoenix and Tempe. Although the foliage can sometimes be burned by the sun, the plants normally take this in stride and still grow and flower. Sunscalded leaves dry up and fall off but they are normally replaced with healthy new leaves. I think you are stressing your plants by overwatering. 12 hours of watering, even with a one-gallon emitter, is excessive. Your drip system should provide about 2 gallons every 3rd. day per plant. If you can't reprogram your system, block the emitters to your roses and water them by hand. Make a basin beneath each plant and flood the basin every 3 days. This should provide enough of a deep soaking to keep the plants from wilting in the hot summer afternoons. When temperatures cool in October you can put your roses back on the drip system and reduce the time the system stays on.
Best wishes with your roses.
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