I know it is a bit early in the season to be talking about tomato fruit diseases, but blossom-end rot is a disease that can be prevented with a little TLC. Blossom-end rot is a symptom of calcium deficiency in tomatoes, which may be caused by low soil calcium, low levels of calcium in the fruit, or other factors like fluctuating soil moisture. In tomatoes, decay is visible on the blossom end. The initial symptom of the disorder is a small darkened or water-soaked area around the blossom end of the fruit, appearing when the tomato begins to ripen.