Well I sprayed the violas early this morning. I used a fairly heavy dosage (top of the suggested range) and sprayed them until run-off. I know from past experience that this might damage them (the spray is slightly phytotoxic) but I think it’s my only chance to save the crop. They will die if I don’t do something dramatic, and I’d rather loose them trying to save them than from being too timid to give them the best chance possible.
Tonight I will fog the whole zone with a biological fungicide (a fungi that eats other fungi in this case). It can only prevent further infection and I am mostly hoping that it will prevent other plants from developing the powdery mildew. It might help the violas’ new leaves, but to be honest, I don’t think I would be able to save the violas without reverting to non-organic methods and I’m willing to do that–our customer base is very concerned with this issue and I’m not willing to lie about how we treat our plants.