Blossom end rot is not caused by a pathogen and disease control products are ineffective at controlling it. It is most common in tomatoes, peppers, melons and eggplant and can occur at any stage of fruit development. Symptoms first appear as a small, water-soaked spot that continues to growth and darken and the fruit develops. The spot may grow to cover as much as ½ of the fruit. The large, dark lesion will eventually dry out and become flattened, black, and leathery.
Blossom end rot occurs when the growing conditions affect the supply of calcium to the developing fruit. When plants can?t get enough calcium the tissues on the blossom end of the fruit break down. Calcium shortages can be caused by several factors: lack of calcium in the soil, low soil pH ties up available calcium, drought stress reduces calcium uptake, and feeding too much causes the plant to grow so fast that calcium can?t move in quick enough.