My plants started doing that last year in August when it was really warm and muggy. It started after rain and me stupidly using an overhead sprinkler to water them. I slowed it by cutting off every leaf that showed any signs of it and pruning to get more air in between the leaves. I didn't cure it though. Once the season was done I ripped up the whole thing, not letting ANY leaves stay behind, and burned it.
Not sure if that is the same thing or not, but those black spots sure look like it. I agree that the whole plant is kinda pale, that might be a different, additional issue.
Including pictures of what mine were doing.
