Blossom end rot - usually from over watering.

BER is caused by a calcium deficiency, usually induced by fluctuations in a plant’s water supply. Because calcium is not a “mobile” element in plants, even brief changes in the water supply can cause BER.

Droughty soil or damage to the roots from excessive or improper cultivation (severe root pruning) can restrict water intake, thus preventing plants from getting the calcium they need. Plants also can develop calcium deficiency and BER if they are growing in highly acidic soil or are getting too much water from heavy rain, overirrigation, or high relative humidity.

One possible solution to calcium deficiency: Pulverize egg shells and work into the soil around the plants.