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Wednesday, Aug. 2, 2006 09:15 pm

Help tomatoes beat the heat

You may love ’em, but they’re prone to trouble

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Photo by Tammy Ljungblad/MCT

The most exciting garden event of the summer arrives when juicy, fresh tomatoes are ready for harvest. Last weekend my family and I were delighted to enjoy an armful of this tasty fruit. We ate our tomatoes with a little salt, with white gravy, and in BLT sandwiches.

Our passion for tomatoes is shared by many gardeners, but, as many home gardeners quickly learn, tomato plants are not without problems: They’re susceptible to diseases, insect infestation, and physiological disorders caused by environmental stresses. Those problems, thanks in part to the recent heat wave, are now evident in many plants.

Blossom-end rot is a common problem on green or ripening tomato fruit. It first appears as a tan-to-brown water-soaked lesion on the blossom end of the fruit (opposite the stem). As the fruit ripens, the dry spot enlarges, become sunken, and turns black and leathery. The sunken spot opens the fruit up to other organisms that cause the fruit to rot. This generally occurs on developing tomatoes during extended hot, dry periods; blossom-end rot occurs during the summer when day temperatures are above 90 degrees Fahrenheit and night temperatures are higher than 76 degrees.

The cause of blossom-end rot is a calcium deficiency in the developing fruit. Calcium is needed for proper fruit development. The deficiency occurs in the plant after large fluctuations in soil moisture. Plant growth slows with limited soil moisture. When water becomes available again the plant grows rapidly, but the uptake of calcium lags behind growth, resulting in tissue breakdown.

One way to control blossom-end rot is to maintain even and adequate levels of soil moisture. Mulching established plants with an organic mulch will help suppress weed growth, conserve soil moisture, and maintain the moisture level evenly. Water plants deeply, then wait five or more days between waterings. Peppers, summer squash, and cucumbers may also exhibit this problem.

Poor fruit set is another disorder caused by extreme temperatures. Blossoms can drop off without setting fruit when temperatures are higher than 90 degrees or below 55 for extended periods of time. Dry soil, excessive nitrogen, and shade can also cause poor fruit set.

Tomato (and pepper) fruits exposed to the sun are susceptible to sunburn or sunscald. The affected areas become dry and sunken, with a papery tan-to-white appearance. Sunscald is most common on green fruit and often affects plants that have lost leaves to foliar diseases or incurred breakage during harvest. Controlling plant diseases and insects that cause defoliation can lessen the chances of sunscald.

Drought followed by a heavy rain or watering can encourage rapid growth during ripening. Growth cracks, the result of too much water applied at one time, can be prevented with maintenance of consistent moisture level in the soil. Some varieties are crack-tolerant.

The Iowa State University Extension offers a fact sheet, found at www.extension.iastate.edu/ Publications/PM1266.pdf, with great photos, descriptions and controls for common problems of tomatoes. Keep in mind purchasing tomato varieties bred for disease resistance can keep a variety of maladies at bay.

Jennifer Fishburn is a unit educator with the University of Illinois Extension, Sangamon-Menard Unit. For more information, go to www.extension.uiuc.edu/sangamon.

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