Hi Rod...
Sounds like BER, or Blossom End Rot...
How's your watering practices?
Lot's of water, or a drying out period..
or too much..??
Also, it's not a disease so to speak...
It's in your soil that is LACKING CALCIUM.....
***But a side note, Another cause of the Blossom-End Rot can be over-fertilization,
especially with the nitrogen (ie; manure, liquid/granular fertilizers, etc..,
which stimulates the
plants growth.
Too much/too fast vegetative growth can increase the transpiration surface and further prevents calcium accumulation in the fruit.
You can apply a foliar feed *on the leaves*
of Epsom Salts and water.. and that will help
with future fruits this season...
For next years season, Applying a layer of lime *then mixed in the soil* several months before you
plant in the low-calcium soils can help prevent blossom-end rot