Answer: Flower Carpet Roses are incredibly resistant to diseases, especially black spot, so I'm surprised your plants have developed problems. Resistant does not mean immune, though, especially if growing conditions are not right (too much shade; poor air circulation), or if the plants are stressed by drought or flood.
Since the black spot fungus infects when the leaf surface is wet, prune surrounding vegetation to allow better air movement in the garden. This helps plants dry more quickly and reduces the time that the fungus can infect the plant. For the same reasons, avoid overhead watering where possible.
Management of this fungus should begin in the dormant season when plants are pruned of old cankers and winter-killed stems. Remove this material from the site because the causal fungus may overwinter on those tissues as well as on old leaves. At the end of the growing season all old leaves should be removed from the site.
In the spring, as new grow emerges, spray with Daconil or Funginex (as directed on the label). Once your plants are healthy again, they should be able to resist further infections.
Best wishes with your carpet roses!
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