Blossom End Rot (BER) does not spread from plant to plant or from fruit to fruit. It is of a physiological nature so fungicides and insecticides cannot prevent or control it. Blossom End Rot often occurs under certain environmental conditions when there are cool nights and warm days. The range in temperature affects the uptake of water and calcium by the developing fruit, and it’s the deficiency in calcium that results in the rotting.
Some varieties of tomatoes are more susceptible to Blossom End Rot than others. When purchasing tomato seedlings be sure to read the labels that accompany the plants. They may tell you if that particular variety is resistant to BER. To help prevent Blossom End Rot from occurring in your plants add crumbled chicken eggshells to the planting hole along with your other amendments. Once planted, try to be sure to keep watering even and consistent. In addition, using organic soil amendments and fertilizer will be helpful. They don’t contain as much salt, which decreases the availability of calcium to the plants.