A website from UGA Cooperative Extension

We shouldn’t be too far away from harvesting tomatoes and peppers.  Which means we are not too far away from County Agents getting calls about blossom end rot.  Blossom end rot (BER) is a condition that can happen with most of the things that we grow in our garden but is most often a problem on tomatoes.  The short story is that blossom end rot is the result of a calcium deficiency.  The long story is trying to figure out exactly why this deficiency is happening.

Calcium is very important for many functions inside a plant but one that is really important is its role in cell wall stability.  Calcium (Ca) deficiency early in fruit development is irreversible and causes what we know as blossom end rot (BER).  Blossom-end rot occurs when cell wall calcium “concrete” is deficient during early fruit development, and results in cell wall membrane collapse and the appearance of dark, sunken pits at the blossom end of fruit.  Gardeners often feel that this is a disease but it is usually the result of improper nutrient or water management.

So how do we manage this disorder?  If your soil test showed that Ca was on the high side (800 lbs/A or greater) then we assume that there is enough Ca in the soil for proper crop growth.  A pH of 6.0 or greater and preplant Ca will also assure enough Ca for proper crop growth.  Commercial growers should submit tissue samples prior to flowering to insure adequate Ca is inside the plants.  This may not be practical for the home gardener. 

Over fertilization with nitrogen and potassium can also lead to deficiencies.  Excess foliar growth requires Calcium and may use what is in the plant rather than it going to the developing fruit.  There is also competition between N, K and Ca for because those two ions compete for uptake into the plant.  If you have the option it may be better to avoid fertilizing late on tomatoes or switch to calcium nitrate instead of 34-0-0. 

Foliar Ca sprays are also available that claim to alleviate BER, but research has not shown this to be true.  It is difficult to get enough calcium through the leaves and into the fruit and the skin of the fruit is impermeable to water once the tomato is the size of a golf ball. 

Finally and most importantly is irrigation.  Calcium can only move into the plant in water.  As the plants get larger and frit begin to develop water use increases.  If we do not keep irrigation constant and increase it as demand increases then we run the risk of inducing a Ca deficiency and causing BER.  Most of the time BER is the result of improper irrigation.  By either over watering or letting plants become to dry we inadvertently cause the Ca deficiency and end up with bad fruit.  I feel that it is also in part due to the large number of fruit that tomato plants will set early. 

This problem can also be seen in peppers, and all of the cucurbits like squash.  It is probably more of a problem on tomatoes because of the crop load and the thickness of the skin on the fruit.  Contact your County Agent if you have questions or comments

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