Writer: D'Lyn Ford
LAS CRUCES Ð Just as a season of hard work begins to pay off with a delicious pepper harvest, gardeners may notice a discolored lesion near the blossom end of some fruit. Although the ugly sight is not a devastating disease, blossom-end rot can be troublesome.
In New Mexico, peppers are most commonly hit by this disorder, but other fruits like tomatoes, squash and melons may also be affected, said Natalie Goldberg, plant pathologist with New Mexico State University's Cooperative Extension Service. Regardless of the plant, the cause and symptoms are the same.
"Blossom-end rot is caused by a physiological disorder associated with inconsistent watering and a calcium deficiency in developing fruit," she said.
Calcium deficiency results from insufficient calcium in the soil or the inability of plants to absorb enough calcium, Goldberg said. The inability to uptake calcium can be caused by high salts; very wet or very dry conditions; excess nitrogen, magnesium, potassium or sodium fertilization; or a combination of these factors.
"As the weather warms and the plants begin to grow more rapidly, the requirements for water and calcium increase. This is the time that fruit begins to show symptoms of blossom-end rot," she said.
Blossom-end rot does not spread from one plant to another, Goldberg said. But it can develop in plants grown under the same conditions.
Gardeners can recognize blossom-end rot by the brown discoloration on the blossom end of the fruit. The spot enlarges as the fruit matures. The lesion tissue becomes sunken and leathery with age. Eventually, secondary fungi or bacteria invade the tissue, resulting in a black or watery appearance.
Blossom-end rot is best controlled by following a management program before and after planting. First, take a pre-plant soil test to determine pH (acid/base) and nutrient levels. Moderate amounts of additional fertilizer can be used to adjust pH levels enough to keep tomato and pepper plants green and vigorous, but not too lush. Then plant in soil with good drainage.
Post-planting treatment should include: watering carefully, using organic or inorganic mulch, avoiding injury to roots by restricting cultivation and fertilizing with additional nitrogen only as needed to maintain "normal" green color.
"The most important factor is to make sure you are watering properly -- avoiding situations of excess moisture and drought stress," Goldberg said. "The soil in the root zone should always be moist enough to easily form a ball. This technique can help determine when you need to irrigate."
Some gardeners also have had success with foliar applications of calcium chloride, Goldberg said. But the success of this spray treatment is erratic, and the results may not be worth the expense, she added.
© 2013 New Mexico State University Board of Regents
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