By Dr. Sharon M. Douglas
Department of Plant Pathology and Ecology
The Connecticut Agricultural Experiment Station
123 Huntington Street
P. O. Box 1106
New Haven, CT 06504-1106
Telephone: (203) 974-8601 Fax: (203) 974-8502
Blossom-end rot of tomato, also called black rot and dry rot, occurs worldwide wherever tomatoes are grown. This disease results in direct fruit losses and levels as high as 50% have been reported. Most cultivars of tomato can be affected by this disease, although differences in susceptibility have been reported. While blossom-end rot is primarily a disease of tomato, it can also occur on pepper although it is not as common.
Blossom-end rot is characterized by a large, brown to black, dry, leathery area at the blossom end of the tomato fruit. The first symptoms appear as small, water-soaked areas, which resemble bruises, on the blossom end of immature or green fruit. These spots usually enlarge and coalesce until the affected area involves anywhere from one-eighth to one-half of the surface of the fruit. The affected tissues begin to dry, shrink, and become leathery. At the same time, the color of this area gradually changes from a bleached yellow to a characteristic dark-brown or black. Blossom-end rot, as the name implies, usually occurs at the blossom end of the fruit (the end away from the stem), but it can occasionally occur at the side of the fruit and can sometimes produce an internal, black lesion that is not visible from the exterior of the fruit. Although symptoms can be found on fruit from any part of the plant, all of the fruit on an individual plant are usually not affected.
Fruit that are affected by blossom-end rot often ripen more rapidly than normal, healthy fruit. In addition, it is not uncommon to find that the affected areas of these fruit are invaded by secondary fungi and bacteria that cause soft rot and fruit decay.
Blossom-end rot is a physiological disease caused by a localized deficiency of calcium in the fruit. Calcium is a nutrient that is required in relatively large quantities by rapidly growing fruit, especially by those cells at the blossom end of the young fruit. When these cells are suddenly deprived of calcium, they begin to break down and symptoms appear. While many factors have been found to trigger this deficiency, water stress generally initiates the problem. Since calcium is not a highly mobile element, periods of water stress as short as 30 minutes can result in blossom-end rot in highly susceptible plants. Moisture problems that interfere with the balance of calcium in the plant can result from cultural practices that promote the development of a shallow root system such as frequent, shallow watering. Moisture can also be a problem in plantings on light, sandy soil with fluctuating moisture levels and on plantings in heavy soils with high moisture-holding capabilities that often become waterlogged.
Other factors that have been found to favor this physiological disease include early planting in cold soils, poor fruit setting, high temperatures, and waterlogged soils. In addition, studies have shown that high levels of ammonium nitrogen in the soil can contribute to disease development by affecting calcium uptake by the plant. In particular, use of manure, especially poultry manure, favors this condition.
There are several strategies that can be used to minimize the development of blossom-end rot in the home garden. The most important thing is to maintain even soil moisture throughout the growing season. This can be accomplished by consistent irrigation and mulching, which help to maintain uniform moisture in the soil. In addition, selecting a proper site with a well-drained soil with good aeration and enough organic matter or humus to retain moisture during dry periods will help to minimize disease development. The soil pH should be maintained above 5.5, preferably 6.5. When calcium-deficient soils are indicated by a soil test, they can be amended with gypsum, superphosphate, or with applications of dolomitic or high-calcium limestone. It is also important to avoid excessive nitrogen fertilizer applications, especially in the ammonium form, just before or during fruiting. When cultivating, care should be taken to avoid destroying or damaging the tender feeder roots, which are responsible for uptake of water and nutrients. Some cultivars of tomato such as Early Girl and Jet Star have been reported to be less susceptible to this disease, although this is usually not considered sufficient to provide dependable control. The plum- or pear-shaped tomato cultivars have been found to be most susceptible.
Blossom-end rot of tomato is a physiological disease that is characterized by a large, brown to black, dry, leathery area at the blossom end of the tomato fruit. This disease is associated with a localized deficiency of calcium at a critical stage in the development of the fruit. This deficiency has been associated with moisture stress and uneven watering. Strategies for minimizing the development of this disease are discussed.