Answer: There are several possible causes for the problem with your peppers. Pesticide burn on the foliage will cause problems like you described. If the plants were sprayed recently, this may be the cause.
Bacterial leaf diseases are another possibility. These are promoted by frequent wetting of the foliage and also by soggy soil conditions. Make sure the soil in pots is well drained and has good air circulation around the plants. Copper based fungicides are a low toxicity option for controlling these diseases.
You didn't mention wilting as a symptom preceeding the plants turning black. This is a common symptom for a variety of soil disease problems which can cause a rapid decline in pepper plants, like you indicated. It is too late to control a root or crown rot once you see the plant turning black.
Check the base of the stem for dark infection lesions or a white fungal mat. Also check the roots of plants that have declined but are not yet totally dead for swollen "knots", or decay (brown rather than cream colored roots). If you see such symptoms submit another question to the web site and we will try to assist you further.
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