Fort Dodge Messenger, IA
07-31-06
This is time of year when blossom end rot appears Good supply of moisture
stops end rot
By SANDY MICKELSON, Messenger staff writer
It’s the time of year for big, red, juicy tomatoes hanging on vines in home
gardens.
It’s also the time of year when lack of moisture and excessive heat combine to
create blossom end rot on those tomatoes.
Blossom end rot appears as a brownish black spot on the bottom of the tomato,
usually at the end of July or early August.
“It’s most common on early-maturing fruit,” said Jim Patton, Webster County
Extension education director. “The fruit that comes on later tends to adapt to the
heat and dryness.”
Blossom end rot is a fungus, but it won’t hurt people, he said. “Most people aren’t
going to eat the tomato because of the way it looks. The end of the tomato starts
to mold. It changes colors and eventually consumes the whole tomato.”
The blossom end rot, he said, is basically caused by imbalances.
“It happens if there’s too little moisture, too much heat, too much nitrogen or too
little calcium,” Patton said, adding that the best way to combat the problem is to
water the tomato plants about one inch of water every week. That inch can be all
at once or divided into two waterings spaced out.
“Just put an aluminum pie plate among the tomatoes,” he said. “If you’re
sprinkling, when that is full, you’ve watered an inch.”
Mulching the tomato garden will help keep moisture levels high by conserving
soil moisture. Because Iowa soil holds an abundance of calcium, there is no
need to apply calcium to the soil, although “when there is too little moisture,
calcium doesn’t get to the tomatoes,” Patton added.
“Too much nitrogen is bad, too,” he said. “If there’s too much nitrogen, things are
out of balance. Most fertilizer has quite a bit of nitrogen in it. It ties up the soil.”
Therefore, excessive fertilization also may contribute to blossom end rot.
Richard Jauron, horticulturalist at Iowa State University Extension,
recommends picking and discarding tomatoes that show blossom end rot.
“The removal of the affected fruit will allow the tomato plant to channel all of its
resources into the growth and development of the remaining fruit,” he wrote in an
ISU Extension newsletter.
Other problems with tomatoes at this time of the summer are fruit cracking and
sunscald, Patton said.
“Fruit cracking only affects large tomato varieties, like beefsteak,” he said.
“Providing enough moisture keeps tomatoes from cracking. Also, if there’s a real
dry spell, then a 2-inch rain, the extremes can cause cracking. That plant is trying
to compensate for something, and what we see is the cracking.”
Cracked tomatoes are edible, he said. They should be washed off and checked
for insects, with the cracked area cut away. “It just doesn’t give you that beautiful
tomato you see in the grocery stores.”
Cracking usually appears at he top or stem end of the fruit. Cracks radiate from
the stem or circle the fruit in concentric rings. Cracking appears when a heavy
rain or deep watering after a long, dry spell results in rapid water uptake by the
plant, Jauron said, adding that “cracking can be prevented by supplying the
tomato plant with a consistent supply of moisture during the summer months.”
Sunscald, Jauron said, appears as shiny white or yellow areas on the sides of
the fruit exposed to the sun. “Later, the affected tissue dries out and collapses,
forming slightly sunken, wrinkled areas. Secondary organisms invade the
affected areas, causing the fruit to rot. Sunscald occurs on fruit exposed to the
sun during periods of extreme heat.”
Sunscald can be prevented, Patton said, by keeping the tomatoes away from
direct sunlight.
“If tomatoes are grown in cages, they tend to be on the insides, and the leaves
act as shade,” he said. “So, cages can be a real plus. When the tomato gets
sunscalded, it’s going to cause a weakness, and any time you create a
weakness, one thing leads to another.”
The ISU horticulture Answerline may be reached by calling 294-1871 between 10
a.m. and noon and 1 and 4:30 p.m..
“Monday mornings are always busy,” Patton said, “so you may have to call back.”