Answer: Based on your description I am unable to tell you if the problem is just related to drought or if there is an insect or disease affecting the plant. These are generally quite healthy plants, so something unusual is certainly happening. First, make sure that your watering is soaking down deep. After you water, wait a few hours and then dig down and check how far it penetrated the soil. Sometimes this is surprising. Watering is done to supplement rain, so you would need to dig down into the soil a bit with your finger to see if and when you need to water again. Your goal is to supplement rain and keep the soil evenly moist but not sopping wet. Shrub roses are actually somewhat tolerant of dry conditions, so careful watering by occasional deep soaking should be adequate to keep them in good shape.
Use several inches of organic mulch to help keep the soil more evenly moist and keep down weeds. This should also be sufficient for winter protection.
Next, avoid wetting the leaves when you water as this can encourage foliage problems. Also do not use a foliar or water soluble fertilizer in very hot sunny weather as this can burn the foliage; overfertilizing in general can cause the symptoms you described as well.
Next, examine the leaves carefully for signs of insects. The symptoms you described could be due to mites or whitefly, both of which would be more prone to appear in a dry season. They can be treated with insecticidal soap according to the label instructions.
If none of the above seem to apply, I would suggest you work with your county extension to determine what is causing the problem. Good luck with your roses.
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