Looks like leaf spot.

click the link to read up and see if you agree it's what your plants have.

Dear joeb:
I'm a Long Islander, too, and funny thing, peppers have been my least troublesome plants over many years. Aside from treating for maggots that get into my bell peppers if I don't spray against them, all other peppers require no maintenance at all.

I wish I had an answer for you, but I will say this. You tend to plant a lot closer than I do. In containers I put one plant per pot. In the ground I separate them by at least 2 feet, 3 if room permits. A big and bushy plant will produce more than 3 plants bunched together. I'm not blaming the close spacing on the start of what appears to be a disease, but it certainly can help the spread of it.

In my experience, bell peppers tend to be weaker & more disease-prone than most other varieties. Mostly for that reason, I have been easing away from them over the years, to the earlier & more reliable pimentos & frying peppers. This year is actually the first (out of many years gardening) that I am growing no bells at all.

"Cubanelle" is one of my favorites... but for me, they were huge sprawling plants requiring 2-foot spacing.

I agree with Justaguy & Ligardener; leaf spot, compounded by overcrowding & overhead irrigation (or frequent rainfall), is the probable culprit. I am somewhat surprised, though, to see it attack potted plants so rapidly - unless you have grown peppers (or tomatoes) in that soil before.

Increasing plant spacing (by removal of a few), mulching to reduce mud splash, and watering by soaking (not spraying) may reduce the severity of the disease. The use of these measures next year - with all new soil - would be even more effective.

I grew bells last year,and had the same exact problem. This year I grew banana, sweet and jalepeno peppers and they have flourished great. I wont be trying bells anymore.

We might have gotten off on a tangent different from joeb's original question, but I'd like to post a word in favor of bell peppers. We love them in our house because we stuff them and freeze them and then eat them throughout the winter. I know that many people are strongly opposed to chemical sprays, but I'm one who finds that limited use of them save me a gr-r-reat deal of frustration and failure. Last year I sprayed my bells twice only, and I didn't lose a single pepper to maggots. The second spray was weeks before I started picking so I was very comfortable with that. A good wash before cooking relieved me of any concern. I'm following the same practice this year.