Bill Starr: Blossom-end rot explained

Published 3:09 pm Monday, April 9, 2018

Now that it has finally started to warm up and hopefully our chance of a last frost has passed it will be time to start planting tomatoes. It would be hard to imagine any home garden that did not have at least a few tomato plants. Tomatoes are considered by many to be the most prized vegetable in the garden. I have already started getting questions about what may have gone wrong with some tomato plants from last year. Most of the descriptions of problems I have been receiving describe a condition called blossom end rot.
Blossom-end rot can be a serious problem with tomatoes. But this disorder can also occur on peppers, eggplant and some melons as well. The main symptom is a dark, sunken, water-soaked area at the blossom end of the fruit. Blossom-end rot appears as small, water-soaked spots at or near the blossom end of the tomato. The spot eventually enlarges and becomes dry, sunken, brown or black, and papery or leathery. This physiological disorder is associated with a low concentration of calcium in the fruit. Blossom-end rot is also induced more often when there is drought stress followed by excessive soil moisture; these fluctuations reduce uptake and movement of available calcium.
Blossom-end rot and can make tomatoes very unattractive. Blossom-end rot is a symptom of calcium deficiency in the fruit. It may be caused by low soil calcium, low levels of calcium in the maturing fruit, or other cultural factors particularly, fluctuating soil moisture. This disorder is usually most severe following extremes in soil moisture (either too dry, or too wet). These conditions can cause a deficiency of calcium available to the maturing fruit, at the spot where damage becomes noticeable. Blossom-end rot is associated with several factors including calcium, nitrogen and soil moisture levels. The severity of this condition can be compounded when two or more of these factors interact with each other.
So how do you prevent this condition? Applying lime several months pre-plant can help prevent blossom-end rot. Selecting sites that have deep, well-drained soils will also help prevent this condition; a large, well-formed root system is better able to take up calcium and other minerals. Early prevention is the key to preventing blossom-end rot. But what can you do if you have just bought a truck load of tomato plants and you have to plant them now? For untested soils you may use the following: mix ½ cup of dolomitic lime, ½ cup of super phosphate or bone meal and 2/3 cup of 6-12-12 or 5-15-15 into the soil in a 2×2 foot area (dug 1 foot deep) for each plant. Mix in well and plant, my own personal soil sample for my garden recommended gypsum (calcium sulfate) to ensure that I would have enough calcium to prevent blossom end rot.
Mulch plants to conserve moisture and to provide a more uniform water supply. Mulches conserve and maintain a uniform moisture supply which helps to reduce blossom-end rot. Keep water supply uniform and regular. Irrigate plants thoroughly and often enough to maintain constant water supply without water-logging the plants.
Foliar applications of calcium can be used but they are not always effective. Apply calcium chloride as a spray if the soil is deficient in calcium and blossom end rot begins to develop. Use 4 teaspoons of 96 percent calcium chloride per gallon of water. Sprays should be applied at weekly intervals until 3 or 4 applications have been made. Prolonged applications of calcium chloride may cause marginal leaf burn. Foliar applications of calcium with products such as Blossom End Rot Stop are only short-term fixes and often work poorly because of poor absorption and movement to the fruit area where it is needed.
Blossom-end rot is a common problem I see every year, and most of the time the condition could have been prevented. Remember controlling blossom-end rot is based on proper calcium nutrition of the crop and optimum irrigation scheduling.
To manage blossom-end rot:
• Maintain the soil pH between 6.2 to 6.8 and supply adequate levels of calcium through applications of dolomitic limestone or gypsum.
• Avoid drought stress and extreme moisture fluctuations by using mulch and deep, timely irrigation once or twice a week.
If you have questions on blossom-end rot or any other concerns, please contact your local extension agent.
Bill Starr is Sumter County agent, University of Georgia Cooperative Extensive Service. Contact him at 229-924-4476.