I've read that if you put down a fresh layer of mulch under the roses in the spring, it prevents the black spot spores from splashing up onto the leaves from rain or watering. I just happened to do that this year without reading that tip and sure enough it worked!
Avoid overhead watering. Improve air circulation. Remove damaged leaves as they appear. Use oat straw as a mulch. It sometimes occurs as a result of potassium deficiency.
CONDYâS CRYSTALS SPRAY FOR BLACK SPOT ON ROSES:
Spray on a solution of 1 litre skim milk, 1 litre soapy water and a pinch or two of Condyâs crystals (potassium permanganate). Reapply about every two weeks.
Mix together 1 litre skim milk, 1 litre soapy water and 1-2 pinches Condy âs crystals. Use as a spray about every 2 weeks.
Mix 3 tablespoons of bicarbonate of soda into 4 litres water and spray the roses. Gather up and dispose of any fallen leaves.
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