Tomato Blossom-end Rot

Tomato blossom-end rot is a disorder caused by calcium deficiency.  The disorder can be aggravated by the application of too much nitrogen fertilizer to tomato plants. Blossom-end rot appears as a round, brown sunken area on the end of the tomato fruit opposite the stem. As a fruit ripens the area turns dry and leathery. The disorder often appears after a period of rapid growth followed by dry conditions, or in periods of heavy rain that caused calcium to leach from the soil.  The physiology of the plant may contribute to the disorder. Calcium in water moves through the plant in the vascular system from the roots to the leaves. Under high moisture stress, the water containing calcium and other minerals moves rapidly to the leaves. Most water is lost through the leaves, and, as a result, most of the calcium is found in the leaves after transpiration has occurred. Fruit does not transpire as much as leaves; thus, less calcium is deposited there, resulting in a localized calcium deficiency in the fruit.