Answer: B. Nisswa, MN A. It sounds like a bacterial soft-rot disease, says John Behling, Swiss chard expert at Alf Christianson Seed Company in Mt. Vernon, Washington. During periods of high temperatures (80 F) and high humidity (70% to 80%), moisture that has settled on the stem provides a perfect environment for bacterial-rot organisms to invade, explains Behling. The first signs are cracking along the stem, which eventually rots. The disease can kill the plant. We usually see it on older, white-stemmed chard varieties in summer and fall, notes Behling. We aren't sure why, but red-stemmed chard doesn't seem to be affected. Older tissue is more susceptible to the disease, likely because large, older plants often have less air circulation around them, creating a better environment for disease. The easiest control method is to remove and destroy any leaves with stems splitting. And since the disease is more prevalent on older plants, try growing a second crop of white-stemmed Swiss chard, starting it in midsummer. Or grow only a red-stemmed variety, such as Rhubarb chard, he suggests.
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