Possibly Anthracnose, which causes black spots or lesions on the stems and leaves. It is an agressive disease, often killing a small plant within a few days. It also attacks other nearby vining plants, including tomatoes. The only recommended treatment I've found, is a soil drench using a fungicide containing copper sulfate, such as Bordeaux Mixture or Kocide 101. Once the fungus attacks a plant, it is usually too late to save it, but treating the soil around healthy plants helps prevent their infection. It is necessary to remove all dead plant material and dispose of it in a sealed plastic bag and treat the soil where it grew with copper sulfate, to prevent the spread of the fungus.
You may be advised to wear rubber or plastic gloves and a mask when handling the soluble copper sulfate powder. It affects my taste buds for a day or so if I breathe in the powder particles. Some may be allergic to it,
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