Answer: Yellowing leaves can be a symptom of disease, especially if you see spots on the leaves or canes, but the yellowing can also be caused by soggy soils. To me, black mulch means black plastic. If this is what you put beneath your roses, it could be holding in too much water (no evaporation because of the plastic). In this case, I'd remove the plastic and replace it with a thick layer of organic mulch such as compost or bark chips. Hope your roses recover soon!
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