Blossom End Rot in Tomatoes

Weekly Newspaper Article for The News-Democrat, Carrollton, KY
 

Photo Courtesy of Tim Coolong, UK Horticulture Specialist

Normally, a hot dry year would favor vegetable production as long as growers have adequate irrigation.  However, when daytime temperatures inch up over 100 degrees Fahrenheit, like we have seen several days this year, we begin to see problems with many vegetable crops.

Pollen begins to die when temperatures reach 100 degrees.  That affects fruit set and several disorders become apparent.

One thing growers might see is blossom end rot, which is simply a rot at the blossom end of a fruit.  Tomatoes usually suffer most, but eggplant, cucurbits and peppers can all succumb to the problem.  It is technically caused by a calcium deficiency in the plant or the fruit.  In many cases, it is not a lack of calcium in the soil, but rather an environmental factor that stops the plant from taking up calcium.

Plants take up calcium via their transpirational system.  As plants move water through the roots to the leaves and out the stomata, calcium moves into the plant.  In areas of severe drought, blossom end rot will appear because there is no water to move the calcium to the plant.  To make matters worse, calcium is immobile in the plant, meaning it cannot move from an area of low demand to an area of high demand, so even temporary deficiencies can cause permanent damage.

When temperatures exceed 100 degrees, many plants will close stomata to conserve water, thus closing the path for calcium to get inside.  Don’t be surprised if you are seeing blossom end rot on your tomatoes that were developing during the most recent heat wave.

Unfortunately, there is nothing you can do to correct the problem.  Once blossom end rot appears it cannot be reversed.  The fruit is safe to eat, just cut off the bottom part and remember you are not able to commercially sell them.

Since summer is only two-thirds over, meteorologically speaking, there are some things you can do to prevent future occurrences of blossom end rot.  If we see high temperatures again, try to minimize them for the plants by providing some kind of shade and giving them adequate water.

For additional information on blossom end rot, take a look at the UK Plant Pathology Fact Sheet, Blossom End Rot.