The Q&A Archives: Black Spot On Dream Roses

Question: I have 12 red Dream Rose bushes; 4 pink Dream Rose bushes; 1 yellow Dream Rose bush; and 1 orange Dream Rose bush that I purchased two years ago. Last year, toward the end of the season just after returning from vacation, I noticed my pink rose bushes had "black spot" which then spread to the red bushes. The pink roses were partly shaded by a Vitex tree, which I have now severely pruned. The bushes are in a row next to a 4' concrete block wall bordering the east side of the house; they get at least 8 hours of sun. We had no rain in this area all season, and I water by drip system and do not water overhead. I treated the bushes with Ferti-lome Blackspot control, but the pink roses lost almost all of their leaves. I picked off and destroyed most all other infected leaves. These are beautiful continuously blooming rose bushes, and my question is what can I do to keep this disease from hitting again this year; and if it does start, what is the best way to treat it?

Answer: Black spot thrives in humid, warm conditions, which aren't too common in the arid Southwest except during monsoon season. It sounds as if you are doing things right in regards to watering. We normally recommend being very careful with watering practices, do not water in the evening, water early in the day so no moisture sits for very long on the foliage. Drip of course alleviates this problem. The best way to prevent it is to clean up and destroy leaf drop and prunings, which causes reinfection, and use a dormant spray that includes lime sulfur. Fungal diseases are usually easier to prevent than to treat. A dormant spray smothers insect eggs and disease organisms before they get started. Apply the spray right after you prune in late winter. Other remedies include neem oil, and the fungicide triforine. You might also want to take a sample of the leaves if it reappears to your County Cooperative Extension office for positive identification. They are at 1510 Menaul NW, ABQ, 505-243-1386.

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