Blossom End Rot on Tomatoes

Home Grown  by Keith Reed
While most gardeners have reported good growing conditions as of late, one problem has recently cropped up. Like so many issues in the plant world, it is likely weather related. Blossom-end rot often catches growers by surprise as the symptoms appear on the blossom end of the fruit (bottom) and can be easily overlooked. Once you have seen it, the disease is easily identified. It begins when the fruit is about half grown as a tan, water-soaked area. The spot enlarges, darkens, and becomes sunken and leathery, rendering the majority of the fruit unusable.

Blossom-end rot is a complex disorder thought to be caused by a localized calcium deficiency in the fruit. Calcium is required in large amounts in the growing parts of the plants. When rapidly growing fruit lack adequate calcium, tissue breakdown results and symptoms appear. Calcium is water-soluble and moves with the plant’s water stream. Under hot and windy conditions, water movement and use is rapid. Since fruit do not transpire water as efficiently as leaves, calcium availability to the outer areas of fruit becomes limiting. Thus high temperatures and wind, widely fluctuating water availability, and drought stress promote blossom-end rot. Conversely, excessive soil moisture for prolonged periods can also damage the root system and its ability to take up calcium. Excessive cultivation too close to the plant can also cause root damage contributing to the problem. Soil deficiency of calcium is rarely a direct cause of this disease in our area. However, excessive growth due to too much nitrogen fertility can sometimes promote excessive blossom-end rot.

As a grower, there are a few things you can do to help minimize this problem. First, try to maintain a consistent moisture level. We have talked about the value of drip irrigation and mulch quite a bit. This is another case where these tools can really pay dividends. As mentioned, calcium deficiency is rarely a problem in our native soil. However, many people grow tomatoes in containers in an artificial soil medium. If blossom end rot is a continual problem, low calcium could be an issue and a soil test would probably be a good investment. Finally, consider avoiding Roma tomatoes as they seem to be particularly susceptible to this issue.

This information was taken from OSU Fact Sheet
EPP-7627 which contains information on several other non-infectious diseases of tomatoes. Also see EPP-7625 and EPP-7626 for additional disease information.

For more information of this or any other horticultural topic, you can contact Keith Reed, the Horticulturist in the Payne County Extension office. Keith can be reached via email at
keith.reed@okstate.edu, phone at 405-747-8320, or in person at the Payne County Extension office, located at 315 W. 6th in Stillwater.

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