Black spot on leaves. What to do?
I noticed some leaves with black spots on them. This seems to be affecting watermelon plants only (or at least for now).
I started the seeds in vermiculite in styrofoam egg containers, then moved them to 7oz plastic cups with two holes for drainage.
In the plastic cups I put a mixture of 1/3 vermiculite 1/3 peat moss and 1/3 mushroom compost. The seedlings have been kept under fluorescent lights (2 different colors). I would turn the lights on them 10-12 hours per day.
The past few days, the weather got pretty warm so we took them outside for few hours a day.
I water with tap water, seedlings in vermiculite every day and bigger ones in plastic cups every other day.
Please look at the picture and let me know what you think is happening.
Here is a link that might be useful: Black Spots Pictures