Roses need regular deep watering, even the Knockout's which are tough shrub types. What appears to be happening is the roses are getting stressed from the high temps and need more water. You may also be dealing with insect problems, since the plants become more susceptible to insect damage once their stressed. Hopefully this article can help:
Answered on July 25, 2011
Was this answer useful?00
Looking for more?
here are more questions about...Hyacinth Plant