Blossom-End Rot (BER) on Tomatoes
A small water soaked spot appears near the blossom end of affected tomatoes and enlarges, darkens and becomes sunken and leathery. Fruits are most commonly affected when they are a third to half grown. BER often occurs on developing fruit when plants have grown rapidly during the early part of the season and then are subjected to prolonged dry weather. Other factors that increase BER are heavy applications of nitrogenous fertilizers, a widely fluctuating water supply, and hot, dry winds. The exact nature of this disease is still debated, but involves and imbalance in amount of calcium in the fruit.
On soils known to be deficient in calcium, use agricultural lime and avoid overfertilizing with commercial fertilizer. Use gypsum as a supplement to liming on calcium-deficient soils. Provide and even supply of water to the plants and avoid any water stress (irrigate during hot, dry periods). Protection from exposure to wind is beneficial, also. Affected plants can be sprayed with a commercially-available calcium preparation.
Please contact your local county extension office for current information.