Experts and BHG readers answer.
Black and yellow spots on rose leaves
This is a fungal disease called blackspot of roses. It's most severe in hot, humid, rainy weather. Some varieties are quite susceptible to the fungus; others extremely resistant. You can spray susceptible plants with a fungicide to prevent development of the disease. (It requires repeated sprayings throughout the summer.) Or consider replacing your susceptible rose with one that has good resistance to the disease.