Those look like marks left by the sucking damage of whiteflies. There are probably nymphs -- that might be what you saw as black, or there might be sooty mold growing on the honeydew the suckingninsects produce -- or it could be ants farming the sucking pests. Weakened foliage will also be susceptible to mildew and other fungal infection.
Remove the badly damaged lower and overlapping foliage -- especially ones that looking at it, your would right away think you wouldn't want to eat that -- no point on leaving it on the plant to attract pests and diseases or spread them. Make sure there is plenty of airflow to prevent fungal issues, then treat for white flies first by rinsing the plant with plain water when you need to water. If there are bunch of them flying around when you shake the plant, use your vacuum cleaner hose/wand to suck them up out of the air (don't get too close to the plant). Sticky traps also work to catch the adults.
The nymphs will also be somewhat more vulnerable to insecticidal soap -- commercial organic ones or home made. Make sure to practice all the precautions including not using in direct sun and -- I rinse right away after giving the solution time to work on the bugs -- only 5-10 minutes depending on plant and pest.