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Blossom-End Rot In A Wet Year?

A frequent question during a wetter than usual growing season is "Why are we seeing blossom-end rot? Isn't it a dry-weather problem?" Blossom-end rot, where the tissue on the blossom end of the tomato (or pepper) breaks down, is generally associated with dry spells, but the reality is much more complicated.

Although blossom-end rot is an extremely common problem, which has been studied for over 100 years, the exact causes - or how to reliably prevent the problem - is not yet understood. Most sources explain it as triggered by a temporary lack of calcium in the blossom-end of the fruit as it is developing. Since calcium moves with water in the plant, this is usually thought to be caused by interruptions in the water supply to the fruit and not so much by an overall calcium deficiency. However, many other factors seem to influence the problem as well. In fact, there is now some thought among scientists that low calcium levels in the fruit are not the trigger for blossom-end rot at all.

The list of other factors that may influence blossom-end rot is a long one.

• stress factors, such as dry conditions, that reduce fruit growth
  
• high temperatures and intense sunlight, especially following cooler, overcast weather
  
• high ammonium-nitrogen levels in the soil
  
• high salinity
  
• susceptible varieties
  
• stress occurring during periods of rapid fruit growth
  
• potassium/calcium ratios in the fruit
  
• high nitrogen fertilization
  
• fluctuations in levels of various growth hormones in the plant

There is now speculation that stress-free, rapid growth conditions create the susceptibility for blossom-end rot in fruit at a certain stage of development. Then, when conditions suddenly turn stressful, reducing growth rates, blossom-end rot may develop. Unfortunately, this does not provide us with a recipe for preventing the problem, so researchers continue to study the disorder.

For the time being, keep in mind that it is not a simple calcium deficiency, so applying calcium is not a reliable solution. When planning for next season, it may also help to look at your nitrogen fertilization levels and if irrigating, try to improve your scheduling based on soil moisture measurements.

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