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By Ramona Frances

Like the light side of the moon, tomatoes still hanging on the vine this time of year and facing the afternoon sun often look bleached. Using UC Master Gardener Handbook as a resource - the term given for that condition is "solar yellowing." The cause, it said, is not only heat that regularly exceeds 85 degrees but high light intensity.

Scott Stoddard, vegetable farm advisor for Madera and Merced Counties does not call it anything exotic either; he calls the condition "sunburn."

Dr. Werner Lipton, a UC scientist, ran tests in the 70s to pinpoint the environmental conditions needed to cause the change in appearance. Lipton concluded that yellow or yellow-orange discoloration on otherwise red fruit was caused by short wave radiation. As he explained it, when lycopen fails to form because of heat and intense light, only caroteins remains for fruit color.

Day temperatures above 85, with fluctuation in temperatures during other parts of the day or night create make vulnerable tomatoes. In tomato production areas where temperatures rise over 85, a much redder tomato develops. To protect tomatoes from sunburn, using shade cloth to block afternoon sun makes sense. Another way to protect plants from the sun is to keep leaves on for good coverage.

"You want a nice strong (plant) cover with lots of weeds. Sunburn typically happens this time of year. Plants will look ragged. You will see mites and powdery mildew and wilt causing leaves to start falling off; then you get the sun burn problem," he said.

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Ramona Frances Ramona Frances is a staff columnist, writer and photographer for the Madera Tribune. You may contact Ramona at 674.8134 ext. 222 or by e-mail ramona (at) maderatribune.net The Madera Tribune online subscription To subscribe or log on, CLICK HERE. For more information first, CLICK HERE.