To a gardener in mouth-watering anticipation of the fruits of his
labors, blossom-end rot looks even worse than the name sounds.

“It’s a common disorder on tomatoes, peppers, eggplants and some
melons,” said Wayne McLaurin, an Extension Service horticulturist
with the University of Georgia College of Agricultural and
Environmental Sciences.

“Blossom-end rot is a symptom of calcium deficiency in the
fruit,” McLaurin said. “It’s usually most severe following
extremes in soil moisture (either too dry or too wet).”

It shows up first as a small, darkened or water-soaked area
around the blossom end of the fruit — hence the name. As the
fruits mature, the spot darkens, enlarges and sinks in. It may
end up as a mere speck or involve more than half of the fruit.

Test Your Soil

A key to preventing blossom-end rot is to test your soil,
McLaurin said. If it’s low in calcium, applying lime several
months before you plant can help.

Once blossom-end rot shows up on the fruit, there’s little you
can do for those fruits. Spraying calcium on the foliage, though,
may help prevent it on developing fruit.

Keep the water supply uniform and regular, too, he said. Irrigate
plants thoroughly and often enough to maintain a constant water
supply without water-logging the plants.

“Tomato plants require 1 to 1.5 inches of water per week during
growth and fruiting, depending on the soil type and weather,” he
said. “Extreme fluctuations in soil moisture can cause an
increase of blossom-end rot.”

Cut Back on Nitrogen

Fast-growing plants with lots of foliage tend to be more
susceptible to blossom-end rot, McLaurin said. So cutting back on
nitrogen levels can help. Use 5-10-10 fertilizer in place of
10-10-10 or 13-13-13 on tomatoes.

Tomatoes, peppers and watermelons planted unusually early, while
the soil is still cold, are likely to have blossom-end rot on
their first fruits. Planting a bit later helps reduce the
problem.

Another thing that helps, McLaurin said, is to remove affected
fruits when you first see symptoms.

“By the time a second set of fruit begins developing,” he said,
“the plant has an expanded root system better able to gather and
deliver calcium to the fruits.”

Other Prevention Steps

Other steps to control blossom-end rot:

• Select sites with deep, well-drained soils. A large
  well-formed root system is better able to take up calcium and
  other minerals.




• Soil test annually. Maintain the soil pH between 6.0 and 6.5
  and soil calcium levels at or above 200 pounds per acre in the
  coastal plain and 400 pounds per acre in the rest of Georgia. If
  the soil calcium is low and the pH correct, incorporate gypsum
  (CaSO₄) into the soil at 1 to 2 pounds per 100 square
  feet.




• Work all fertilizer, lime and/or gypsum into the soil 8-12
  inches deep. Avoid ammonium nitrate if possible. Ammonia inhibits
  the uptake of calcium.




• Fertilize tomatoes with several smaller side-dressings, and
  then only after the tomatoes are the size of a nickel.




• Mulch plants to conserve moisture and provide a more uniform
  water supply. Straw, pine straw, ground leaves or newspapers are
  all good mulches.




• Avoid cultivation and hoeing. If you have to cultivate, keep
  it shallow to avoid root pruning.




• Avoid severe pruning. Severely pruned tomato plants are more
  prone to develop blossom-end rot.

“Remember,” McLaurin said, “controlling blossom-end rot is based
mainly on proper calcium nutrition and proper irrigation
scheduling.”

For more on blossom-end rot, check McLaurin’s publication on the
Web at www.ces.uga.edu/Agriculture/horticulture/
blossom-rot.html. Or contact the county Extension
Service office.