Indoor growers probably won't get this problem. At this time of year I can get a small second crop, but I always get the same problem: black fungus (mould) growing on the leaves. Since I'm a chemist I have come up with an experimental treatment. The requirements are: 1. Must not damage or be toxic to the growing plant. 2. Must be safe for humans. (no commercial fungicides) 3. Should be cheap (outdoor grows, remember!) 4. Should be easy to obtain the ingredients and easy to make. What I have done is use SODIUM BENZOATE, which is a common, cheap, and easily obtained preservative used in sodas drinks; since it doesn't work unless the pH is below 5.5, I added a little CITRIC ACID. Method to make 1 litre of sprayable anti-fungal:- 1 kg distilled or bottled water. 5 grams sodium benzoate powder. 5 grams citric acid powder. Divide the water into two equal batches. To one, add and dissolve the sodium benzoate. To the other, do the same with the citric acid. When both are fully dissolved, mix the two together. Put into a spray bottle. I have been testing this for a week and it seems to be effective and has not damaged the plants. It's probably not as effective as commercial fungicides but I don't think I want to be using those on something I consume.