Blossom-end rot is a serious disorder of various fruits and vegetables such as tomatoes, melons, peppers, and eggplant. Growers may notice a dry sunken leathery lesion that has developed on the blossom end (opposite end of stem) of the fruit. This is an abiotic disease caused not by a pathogen but by the plant's growing conditions.
Blossom-end rot begins as small tan, water soaked lesions on the blossom end of the fruit. The lesion enlarges and becomes sunken, dark, and leathery. On peppers, the lesion is more commonly found on the side of the fruit towards the blossom end. Also, on peppers it can be sometimes confused with sun scald. Fruit infected by blossom-end rot ripen early, especially tomatoes, and often become infected with secondary organisms such as Alternaria spp.
The cause of blossom-end rot is not by a pathogen, but a physiological disorder of low calcium in the fruit. Calcium is required for normal cell growth and in relatively high concentration for new tissue growth. Rapidly growing fruit will begin to breakdown at the blossom end because that is the last place of the fruit tissue to receive calcium and also the area with the lowest concentration of calcium.
In rapidly growing plants, calcium cannot move to those rapidly growing areas quickly enough. Because calcium moves with water, fluctuations in water supply can cause blossom-end rot. Large fluctuations in soil moisture inhibit uptake and movement of calcium. Excessive nitrogen promotes rapid plant growth, which can cause low concentrations of calcium to occur in plant tissue. But other causes such as low calcium levels in the soil or high amounts of cations in the soil which compete with calcium uptake can also cause blossom-end rot.
Proper fertilization and water management help to minimize this problem. Avoid over fertilizing the crop, especially with ammonical forms of nitrogen. Also avoid allowing the soil to become too dry and then overly wet. Wide fluctuations in soil moisture inhibit calcium uptake and movement. If calcium is deficient or high salts occur in the soil, then foliar applications of calcium may be beneficial. Otherwise foliar applications are of little value because of poor absorption and movement into the fruit.