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Chicago Urban Gardening

The day to day experiences of a University of Illinois Extension Urban Horticulture Educator in Chicago, Illinois
Blossom END ROT TOMATOr3

Tomato: Blossom-End Rot

Posted by Ron Wolford -

Blossom-end rot is a summer disease very common in tomatoes and fruit vegetables such as peppers, eggplant, and sometimes melons and summer squash, said a University of Illinois Extension horticulture educator.

"It is a non-pathogenic disease, a physiological disorder," said Maurice Ogutu. "It is a symptom of calcium deficiency in the fruit. Calcium deficiency may be caused by low soil calcium, low calcium in maturing fruit, or fluctuating soil moisture. It is usually severe following extremes in soil moisture conditions--either too dry or too wet."

Calcium, he explained, is required in large amounts by fruits for normal cell growth. When a rapidly growing fruit is calcium-deficient, normal cell growth is interrupted and the tissues start breaking down. This leaves a characteristic dry, sunken lesion at the blossom end of the fruit.

"Blossom-end rot is induced when calcium demand exceeds supply," he said. "This may come as a result of low calcium levels or competition for calcium uptake with other mineral nutrients in the soil.

"The other factors that can predispose plants to blossom-end rot are very little moisture in the soil caused by drought stress, excessive soil moisture fluctuations which reduce uptake and movement of calcium into the plant, or rapid vegetative growth due to excessive nitrogen fertilization."

In tomatoes, the first visible symptom of this disorder is a small, darkened or water-soaked area around the blossom end of the fruit. The spot darkens, enlarges, and becomes sunken as the fruits mature. Larger lesions may show concentric rings. The affected tissue is leathery and firm unless invaded by secondary decay organisms.

"Blossom-end rot usually causes the fruit to ripen prematurely and it then becomes inedible," Ogutu said. "Sometimes the affected areas become infected with secondary pathogens which appear black on the affected areas. The affected area can be small or may cover most of the fruit.

"Blossom-end rot appears as tan in color in peppers and should not be confused with sunburn that appears whitish in color mainly away from the blossom end. It appears mainly on the first cluster of fruits in tomatoes and peppers."

The disease can be controlled by selecting sites with deep, well-drained soils where plants will develop well-formed root systems for optimal uptake of calcium and other mineral nutrients.

"Test your soil after every three years and lime it if needed," he said. "Avoid use of ammoniacal nitrogen fertilizers such as ammonium nitrate as the ammonium inhibits calcium uptake. Do not overfertilize the plants at planting.

"Provide adequate moisture throughout the growing season and mulch the plants. Avoid severe pruning of the plants, and when controlling weeds, do not dig deep closer to the base of the plant. Foliar sprays can be used as a short-term measure but their absorption by the fruit is very poor. Calcium chloride can be used as a foliar spray only in tomatoes and should be sprayed when it is not too hot to avoid burning the leaves."

Source: Maurice Ogutu, Extension Educator, Horticulture, ogutu@uiuc.edu

Photo: University of Illinois Extension




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