Remove the worst affected leaves since they are no longer performing photosynthesis and contribute to other leaves becoming infected. Neem oil is one organic treatment. Other home recipes have uneven results. It is important to spray home remedies on a small portion of the plant and wait several days to see if the spray damaged the plant. Several home-made recipes follow: I can not vouch for their effectiveness or safety.
Blackspot and mildew control and prevention: Milk spray. Mix one part milk to 9 parts water. Spray every 5-7 days X 3 applications.
Powdery mildew formula: to one gallon water, add 4 tsp baking soda and 1 Tbl horticultural oil. Spray all leaf surfaces every 3 days X 3
Powdery mildew recipe: to one gallon of water, add
1 Tbl baking soda
2 Tbl Safer SunSpray (fine agricultural oil)
with or without anti-transpirant. Anti-transpirant keeps fungal spores from spreading.
