9ac1836f_Pests___Diseases__Problem_Symptom
[Cause] Downy mildew, a fungal disease that is not at all common in the Puget Sound area, but does show up once in a great while. Spray damage can look similar - blackened or browned patches on the upper surfaces of the leaves, but the leaves don't fall off. If you think you might have downy mildew, call one of our Consulting Rosarians for a confirmation before embarking on control measures. [Solution] Prune out and destroy (don't compost!) all affected parts of the plant. Spray remaining plants with Stature, Subdue, or Alliette. You will probably have to get these mail-order. Follow label directions to the letter. Do not add anything else to the spray mix. Downy mildew can kill a rose plant within weeks so act fast. You may want to simply dig out and burn the affected plants. Clean all tools before using on unaffected plants. [Problem/Symptom] 
Black patches appear on upper leaves, then spread to rest of the plant. Unlike blackspot, these spots are angular or squared-off, stopping at leaf veins, and don't have a yellow halo. Leaves fall off within a few days of patches appearing. There may be long black streaks on the canes.
Pests & Diseases
Problem/Symptom