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 have been getting several calls from folks that appear to have the same tomato malady as you. The culprit is blossom-end rot (BER), and its 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, lesions often become covered with a black mold.
Now that you know what it is, let’s discuss the causes. BER occurs as a result of 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) can restrict water intake and prevent the plant from getting the calcium it needs. Also, if plants are growing in highly acidic soil or getting too much water from heavy rain, over-irrigation, or high relative humidity, they can develop 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 two to four months before planting tomatoes.
• Apply the required amount of fertilizer, when necessary, based on soil test results for tomato. Applying too much fertilizer at one time can induce BER. Following soil test recommendations is the surest way to fertilize properly.
• Use mulch, such as pine straw, decomposed 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.
• This is the step you have been waiting for. If your plants develop BER, spray them with a calcium solution at the rate of four 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. You should spray two or three times each week, beginning when the second fruit clusters are blooming. (One note: spraying 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 as to their performance.
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.
I hope this information has been helpful. Following these simple steps should greatly reduce your BER woes in the future. Happy gardening!
This column includes research-based information from land-grant universities around the country, including Alabama A&M and Auburn Universities. Email questions to Bethany@aces.edu or call 205- 612-9524. Like us on Facebook. Follow us on Twitter. The Alabama Cooperative Extension System (Alabama A&M University and Auburn University), is an equal opportunity educator and employer.