By MARION BARNES
Senior County Extension Agent
Clemson University
For many people, there are few things more enjoyable during the summer than a bacon, lettuce and tomato sandwich (BLT) made with fresh ingredients like home-grown tomatoes. With fresh vegetables starting to come in, many home gardeners are often distressed when they notice their tomatoes begin developing rotten spots on the bottom or blossom end of the fruit.
This disorder is known as blossom-end rot (BER) and is especially common with tomatoes. Squash, peppers, cucumbers and watermelons are also susceptible.
The first sign of blossom-end rot is usually a light colored, water-soaked spot that appears on the bottom or blossom-end of the fruit. The affected tissue breaks down over time, enlarges, darkens and can become leathery. The affected fruit may ripen prematurely and BER often affects the first tomatoes on the plant.
Blossom-end rot is symptom of a nutritional deficiency due to the lack of calcium in the fruit. It can be caused by low calcium in the soil or a change in the plant’s water supply — too dry or too wet. Since calcium is not highly mobile in the plant, even brief changes in the water supply can cause blossom-end rot.
Actively growing plants must have a continuous supply of calcium to prevent blossom-end rot from occurring. Root damage caused by improper cultivation or burning from fertilizer and waterlogged soils can also lead to blossom-end rot by interfering with water and nutrient uptake by the plant.
While blossom-end rot can be a common occurrence, it is correctable with good cultural and fertility practices. The following are a few suggestions for controlling blossom-end rot in tomatoes:
• Grow tomatoes on well-drained soils with adequate organic matter content.
• Avoiding nutrient deficiencies that can cause blossom-end rot begins with a soil test. Apply lime and fertilizer to soil test recommendations. The desired soil pH for growing tomatoes is between 6.0 and 6.5.
• Over fertilization of nitrogen and potassium during early bloom and fruiting can increase the chances of BER. Avoid ammoniacal nitrogen fertilizers (ammonium nitrate or ammonium sulfate) for side-dress applications (beside or around the plants), as ammoniacal nitrogen competes with calcium uptake.
• Deep cultivation near plants after fruit set should be avoided to lessen chances of damaging roots, especially during dry weather periods.
• A constant supply of water during fruit development stages is critical in avoiding BER. Depending on the soil type and water-holding capacity of the soil, tomatoes require 1-1.5 inches of water, either supplied by rainfall or irrigation, per week. Remember, extreme fluctuations in soil moisture contribute to BER. Use mulches to conserve water.
• Plant different varieties of tomatoes since some varieties are more sensitive to the conditions that cause BER.
• Although BER does not spread from plant to plant or fruit to fruit, infected fruit should be removed as soon as noticed, since the damaged tissue may serve as entry points for other disease-causing bacteria and fungi.
For more information on blossom-end rot in tomatoes check out the Clemson University Home and Garden Center publication HGIC 2217, Tomatoe Diseases and Disorders.
Information for this article was taken in part from “Blossom-end Rot,” Michigan State University Extension Service; “Blossom-end Rot in Tomatoes: Causes and Prevention,” Auburn University Extension Service.
