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First Report of White Mold (Sclerotinia sclerotiorum) on Soybean in Maine

White mold or Sclerotinia stem rot (Sclerotinia sclerotiorum (Lib) de-Bary) was first observed on soybean varieties in a variety trial at the Maine Agricultural and Forest Experiment Station, Presque Isle, and in commercial soybean fields in late July and August 1997. Symptoms and signs included stem bleaching, fluffy white mycelial growth on soybean stems and foliage, and presence of sclerotia typical of white mold. Disease assessment, based on symptoms, was conducted on the varieties in the trial in the experiment station. Field observations on disease occurrence were also conducted in commercial soybean fields in northern Maine. In the variety trial experiment, mean incidence (%) of white mold ranged from 0 to 6.8% on Lambert, APK007, P9092, P9132, and Stine varieties. No white mold was detected on P9071, P9007, Korada, Bravor, Ugo, APK020, and Aquillon varieties. Of the infected varieties, incidence of white mold was detected in 10 of 33 fields examined. This is the first report of the occurrence of white mold on soybean in Maine. Because of large-scale commercial potato production in the region, and previous occurrence of white mold on potato, it is likely that the pathogen is present in soils of various commercial potato fields in Maine. Precautions should, therefore, be taken in introducing resistant varieties and ensuring proper rotation and cropping sequences as soybean production increases in Maine.