There is no need to destroy them just because of black spot. Spray them all with a fungicide called Mancozeb every 7 to 10 days for 3 to 4 sprayings. Once the black spots are on the foliage, they do not go away. However new foliage should be black spot free if the fungus has been killed. I have found mancozeb to be the best to stop black spot in its tracks! It will leave a yellowish powdery looking residue upon the foliage and canes but that is part of how it works. Once the new foliage comes in clean, keep the rosebushes sprayed with an earth friendly fungicide called Green Cure every 10 to 14 days unless wet conditions dictate more often. Mix it at the Cure Rate at all times for a higher degree of protection. Both products are available at Amazon.com.
Answered on September 6, 2018
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