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​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.

Blossom End Rot is caused by a nutrient deficiency.JPGBER 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.


Comments

kerry smith

7/15/2014 3:09 PM
A common question about mulch - "Can I use pinestraw? I heard it makes my soil too acidic for vegetables." 

Answer: Pine straw decomposes very slowly and will not quickly or dramatically impact soil pH.  As a general rule, any organic material you have on hand is a good mulch.  Wet newspaper or cardboard underneath works well too.

Tom Dingledy

7/15/2014 3:47 PM
Is Epsom salt an effective treatment for BER or is calcium nitrate or calcium chloride the best way to go? Thanks.

kerry smith

7/15/2014 4:01 PM
Epsom salts contain hydrated magnesium sulfate, two micro-nutrients crucial to plant growth, but not relative to BER
• Sulfur (~13%) is crucial to the inner workings of plants, but it is rarely low enough in the soil to cause problems - plus plants don't use much of it per life cycle.
•Magnesium (~10%) can become scarce in soil, usually because of erosion or depletion of the top soil or a pH imbalance. Magnesium helps plants build strong cell walls, allowing the plant to take in other nutrients it needs. It also aids some plant processes like seed germination and photosynthesis.
I suspect that the water a gardener adds when applying Epsom salt is the better part of this remedy recommendation, but over time could assist the plant in more efficient intake of calcium.
Calcium nitrate is the better remedy and gets right to the matter - a calcium deficiency.

Richard Anderson

8/20/2014 9:34 AM
I haven’t had trouble with Blossom End Rot (probably because I have alkaline soils), but I have seen it in other’s gardens a lot.  It’s such a frustrating problem!  Thanks for this informative article.  I don’t think most people realize that it’s a problem within the plant rather than a fungus or something causing the issue.

Richard

Rudy Caudill

8/24/2014 9:01 AM
Sounds good.  Will spraying with blossom rot sprays help? If so, when can it be used? 
where do you send soil samples for gardens?  We have kits for our pastures.

kerry smith

8/25/2014 8:13 AM
Hi Rudy,
You can use the calcium sprays for BER anytime - these come premixed under various brand names.  Soil sample info can be found here - http://www.aces.edu/anr/soillab/ - find the address on this page and submission forms through the tab, "forms," at the top.  Remember to specify your crop at vegetables where requested on the form and any other specifics as these make the test recommendations more accurate for your application.  As well notice the "calculators" on the forms page.  These can help you with fertilizer usage.
Good luck with your fall/winter garden!