Causes and Prevention of Blossom-End Rot in Tomatoes

            Tomato growers must take care to avoid blossom-end rot (BER), a disorder that can dramatically reduce both quality and quantity of tomato fruit.  By using a few simple irrigation and fertilization practices, damage due to BER can be prevented or reduced.

            “Blossom-end rot is a physiological disorder, not a disease,” says Dr. Joe Kemble, a horticulturist with the Alabama Cooperative Extension System.  It is easily identified as a brown, leathery rot developing on or near the blossom-end of the fruit.  It starts with a dry brown lesion the size of a dime, generally increasing in diameter as the condition worsens.  In time, lesions often become covered with a black mold.

            BER is caused by calcium deficiency, usually induced by fluctuations in the plant’s water supply.  Droughty soil or damage to the roots from excessive or improper cultivation (severe root pruning) can restrict water intake, preventing the plants from getting the calcium they need.  Also, if plants are growing in highly acidic soil or are getting too much water from either heavy rain, overirrigation, or high relative humidity, they can develop calcium deficiency and BER.

            Kemble offers the following steps to control BER:

·         Keep the soil pH at 6.0 or 6.5. Perform a soil test and apply the recommended rate of lime, using dolomitic or high-calcium limestone.  Be sure to apply lime two to four months before planting tomatoes.

·         Apply the required amount of fertilizer, when necessary, based on soil test results for tomato.  Applying too much fertilizer at one time can induce BER.  Following soil test recommendations is the surest way to fertilize properly.

·         Use mulches to conserve moisture. Use pine straw, straw, decomposed sawdust, plastic or newspapers. Mulches conserve soil moisture and reduce incidence of BER.

·         Give plants adequate water. Tomato plants need about 1.5 inches of water a week during fruiting.  Extreme fluctuations in soil moisture can result in a greater incidence of BER.

·         If plants develop BER, spray them with a calcium solution at the rate of 4 pounds of calcium nitrate or calcium chloride per 100 gallons of water (or 4 level tablespoons per gallon of water). Be careful with calcium chloride.  If day temperatures are greater than 85 to 90 F, calcium chloride can burn plants. Under high temperatures, use calcium nitrate. Spray two or three times each week, beginning when the second fruit clusters are blooming.  Spraying calcium is not a substitute for proper irrigation and fertility management.

·         Some varieties of tomato tend to be more sensitive to conditions that cause BER. Try growing several varieties, and keep notes as to their performance.

·         If you experience severe problems with BER, remove the infected fruits. Once a fruit develops BER, it wil not regrow or repair the infected area. If the fruit is not removed, the damaged area could serve as an entry point for disease-causing bacteria or fungi.

Source: Dr. Joe Kemble, Horticulturist, Alabama Cooperative Extension System,(334) 844-3050