One of my Granadero tomato plants is showing signs of blossom end rot. Here's what it looks like:
So, off to Google for some information...
Symptoms appear at the blossom end of the fruit. The darker spot enlarges and darkens as the fruits develop.
Yay! The disease does not spread from plant to plant, or even fruit to fruit. It is physiological, and not due to an external organism. The cause is lack of sufficient calcium uptake. Blossom end rot is common when rapidly growing plants are suddenly exposed to a period of drought, like we had the past couple of weeks before the big rains. The problem can occur not only in tomatoes but also pepper, squash, cucumber and melon fruits.
It is recommended to use fertilizer low in nitrogen but high in superphosphate; "in emergency situations, foliage can be sprayed with calcium chloride solutions."
I purchased a fertilizer that contains calcium and that can be sprayed on the leaves or added to the soil. I'll report back on the results, and whether I manage to save some of the tomatoes on that plant or end up discarding the entire plant.