Plant Pathology Infobytes

February 4, 1999
Blossom-end Rot of Tomatoes - Planning Ahead Pays Off

Dark brown or black blotches on the bottom of tomato fruit is a sure sign of blossom-end rot. This problem shows up in many home vegetable gardens across Mississippi each season, but there are steps which can be taken in late winter which will help prevent blossom-end rot in the next crop.

Before covering control measures for blossom-end rot, let's make sure you know what it looks like, since home gardeners sometimes confuse the problem with other tomato diseases. The first indication of blossom-end rot is a slight discoloration, water-soaked in appearance, occurring at the blossom-end (bottom) of the fruit. This area enlarges rapidly, producing a brown or black sunken area. The skin over the affected area becomes dry and leathery.

Blossom-end rot is caused by a shortage of calcium in developing fruit. This may be due to a lack of calcium uptake from the soil or to extreme fluctuations in water supply. Tomato plants growing in soils low in calcium and soils which are alternately wet and dry during fruit development are more likely to show blossom-end rot. Also, this problem generally is more severe when plants are fertilized too heavily with nitrogen fertilizer.

It's never to early to begin plans for correcting past garden problems, so give the following recommendations a try. They should reduce fruit losses to blossom-end rot:

  • Collect a soil sample in the off-season (now is a good time to carry out this project) to determine levels of calcium so that any calcium deficiency problem can be corrected through application of lime. This should be done before the spring planting season -- if you're not sure about the procedure for collecting soil samples, check with the County Extension office for details.
  • Blossom-end rot is also related to moisture supply, so during the growing season, don't forget to keep a close eye on your plants, monitor soil moisture, and irrigate before signs of moisture stress are apparent. As a general rule, during the growing season, tomato plants need at least one inch of water per week in the form of rain or supplemental irrigation.
  • Consider mulching your tomato plants, since this practice will help maintain uniform soil moisture conditions.
  • If blossom-end rot should begin to show up, apply several sprays of calcium chloride (available at garden supply stores under a variety of trade names). Follow label directions. Sprays containing calcium chloride will help to prevent further development of the problem but will not cure fruits already affected.
  • Remove fruit showing symptoms of blossom-end rot when the problem is first observed. This practice will reduce the drain of food and nutrient materials which otherwise would be available for development of other fruit not affected by blossom-end rot.
  • It's especially important to follow a recommended program of fertility and avoid excessive application of nitrogen fertilizer.

If you have questions about blossom end-rot, or any other gardening problem, give us a call at the County Extension Office.



Written by the late Dr. Frank Killebrew

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