I am growing Black Beauty eggplants in containers on a screened-in porch in north Florida, zone 9a. The plants have some black spots on the undersides of leaves. It's been raining a lot lately and it is very humid as always at this time of the year here, so I am not sure if it caused by moisture or by some kind of pests.

Can you please help me identify what it is and how to control it? Thank you!