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Blossom end rot: Is it a rot of blossoms or something more?

August 10, 2021  By Dr. Mohyuddin Mirza

I recently received an email which prompted me to write this article.

“We are seeing a lot of this on our peppers mostly on the poblano but also some on banana and sweets. We are regularly brushing off fried blossoms to prevent blossom end rot but wonder if we are not getting them all or are we too late. Could this be something else?”

The email was accompanied by a picture of the peppers shown above.


The typical symptoms of rot were clearly located at the blossom end of the fruit, so the grower thought that this could have been due to shrivelled blossoms and removed them, which did not improve the situation.

In tomatoes, blossom end rot (BER) symptoms are more common at the blossom end, however in peppers especially for fruit which are not blocky, the symptoms can appear away from the blossom end and on the sides as well. In tomatoes, symptoms can also appear on the sides of the fruit and BER is more common on larger fruited varieties. I have seen it in cocktail and roma tomatoes as well this year, and heat is the major reason.

A very comprehensive article was published in Greenhouse Canada on BER by  Dr. Fadi Al-Daoud and Dr. Xiuming Hao:

Check out this article for up-to-date information on BER, especially as the heat wave continues. I am receiving more reports about this disease, and growers may lose a few clusters during the midseason.

Understanding BER in layman’s terms:

First thing to note: BER is not a disease caused by blossoms hanging onto the fruit. It is a physiological condition where calcium deficiency occurs in the walls of rapidly expanding fruits of tomatoes and peppers.

When these fruits are sizing up, the demand for calcium increases to build the cell walls of the skin, and if there is a temporary shortage due to whatever reason, the skin collapses, dies off, turns brown and then black and thus fruit is rendered unsaleable. It can affect young, green fruit or more mature fruits.

Know about this stubborn element – calcium

I assign the term “ stubborn” to calcium because it does not move inside the plant as easily as nitrogen and potassium. Every element which plants need to grow and prosper have an electrical charge: + or -. Calcium has two positive charges (Ca2+) and is heavier compared to potassium (K+). Another term we use is bivalent for calcium. All this mean is that plant has to spend more energy to absorb bivalent ions compared to monovalent ions. Calcium gets fixed in the cell walls, making it part of the skeleton, and it cannot be moved to other parts of the plant, like the fruit, if there is a temporary shortage.

It is also important to know that within the plant’s transport system, it is moved with active transpiration from the leaves. So if there is high humidity in the greenhouse, calcium uptake may be slowed down because of slower transpiration – the loss of water from the leaves to the surrounding air.

Here are a few practical steps you can take to reduce the incidence of BER:

  • Check if enough calcium is being fed in the fertilizer program. Many smaller growers think that they are using a complete fertilizer and thus don’t add enough calcium. Make sure you know the level of calcium in your fertilizer. Sometimes growers think that there is enough calcium in their water supply or had added enough lime (calcium carbonate) to their growing mix.
  • Even when you are using calcium nitrate, I have seen instances where the injector is not working properly and plants are not getting enough calcium. The easiest way to check is to see if the stock barrel volume is decreasing.
  • I have also seen some growers with one fertilizer injector where they feed NPK in one watering then calcium nitrate in the next without flushing the irrigation lines. If the irrigation lines are not flushed with water, then phosphate, sulfates and calcium can precipitate, causing two problems. One is that these two elements become unavailable to the plants, and the second is that the precipitate can plug up the drippers
  • Paying attention to the pH of the fertilizer solution is also vital. The recommended range for pH of the fertilizer solution is between 5.8 and 6.2. If the pH rises over 6.4, then calcium can bond with phosphate and render them unavailable to the plants..
  • Check your watering practices. With this heat wave, it is important to keep the root zone moist throughout the daylight hours. If your computer allows, then irrigate based on sunlight. For each 100 joules, apply 300 ml of water per m2 of greenhouse area. If the light is 2000 joules, then you need to apply 6 L of water/m2. If there are 3 plants/m2, then each plant will get 2L of water. If you are not set up with a computer, then irrigate more frequently. I have been dealing with a tomato grower who only irrigates four times daily and had a really bad case of BER recently on a set cluster.
  • In the summer heat, tomatoes and peppers can remove water from the growing medium selectively to meet their transpiration needs, keeping themselves cool and thus the Electrical Conductivity (EC) can increase in the leach. I am finding EC values as high as 5.0in tomatoes, which is a cause for concern because water uptake will be slowed down at EC values like this, further complicating BER.
  • And the final point is, try your best to control climate, shade your greenhouse, and remove or add humidity. In the prairies, it is so dry that growers have to constantly add humidity through misting or fogging. One of the other challenges is that beside fighting with BER, the fruit size is decreasing and they are maturing before sizing up fully and that is due to not being able to supply enough carbon dioxide.

Mohyuddin Mirza, PhD, is an industry consultant in Alberta. He can be reached at

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