​Q. I am having trouble with my tomatoes.  I have noticed brown spots near the base of the fruit.  They start out small but continue to increase in size.  What is this disease and how can I get rid of it?

A.  Well, if it is any consolation, you are not alone.  We've had several calls from folks that appear to have the same tomato malady as you.  The culprit is Blossom-end rot (BER), and it is actually a physiological disorder, not a disease.  It is easily identified as a brown, leathery rot developing on or near the blossom-end of the fruit.  It starts with a dry brown, dime-sized lesion, generally increasing in diameter as the condition worsens.  In time, the lesions often become covered with a black mold. It can appear on both green, immature fruit and ripening fruit.

BER is a calcium deficiency within the plant.  This deficiency is typically induced by fluctuations in the plant’s water supply.  Due to the fact that calcium is not a highly “mobile” element in the plant, even brief changes in the water supply can cause BER.  Droughty soil or damage to the roots from excessive or improper cultivation (severe root pruning with a tiller) can limit water intake, preventing the plant from getting the calcium that it needs.  Also, if plants are growing in highly acidic soil or are getting too much water from heavy rain, over-irrigation, or high relative humidity, they can develop a calcium deficiency and BER.  To control BER, take the following steps:

• Keep the pH of the soil at 6.0 to 6.5.  Perform a soil test and apply the recommended rate of lime, using dolomitic or high-calcium limestone.  This step should take place 2 to 4 months before planting tomatoes.
• Apply the required amount of fertilizer when necessary based on soil test results for tomato.  Following soil test recommendations is the surest way to fertilize properly.  Applying too much nitrogen fertilizer at one time can induce BER. The newly forming leaves also need calcium and they rob the fruit of what it needs.
• Use mulches, such as pine straw, composted sawdust or newspapers, to conserve moisture.  Give your plants adequate water.  Tomato plants need about 1.5 inches of water per week during fruiting.  Extreme fluctuations in soil moisture can result in a greater incidence of BER. Use drip irrigation or soaker hoses to keep the soil consistently moist, but not excessively soggy.
• If your plants already have BER, drench the root zone with a calcium solution at the rate of 4 level tablespoons of calcium nitrate or calcium chloride per gallon of water.  If day temperatures are greater than 85 to 90°F, do not use calcium chloride, as foliage burn can occur.  Calcium nitrate is the better option for our hot summer days.  One note - applying calcium is not a substitute for proper irrigation and fertility management.
• Some varieties of tomato tend to be more sensitive to conditions that cause BER.  Try growing several varieties and keep notes on the performance of each.
• If you experience severe problems with BER, you should remove the infected fruits.  Once a fruit develops BER, it will not re-grow or repair the infected area.  In fact, the damaged area could serve as an entry point for disease-causing bacteria or fungi.

In general, it's easier and cheaper to take steps early to prevent blossom end rot in tomatoes than it is to treat the problem once it shows up.  I hope this information has been helpful.  Following these simple steps should greatly reduce your BER woes in the future. 

Garden Talk is written by Bethany A. O’Rear of the Alabama Cooperative Extension System, C. Beaty Hanna Horticulture & Environmental Center, which is based at the Birmingham Botanical Gardens.