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Effects of Moisture, Chloropicrin, and Methyl Bromide Singly and in Mixtures on Sclerotia of Sclerotium rolfsii and Verticillium albo-atrum. Donald E. Munnecke, Professor, Department of Plant Pathology, University of California, Riverside 92521; M. J. Kolbezen(2), and J. L. Bricker(3). (2)(3)Professor emeritus, and staff research associate, respectively, Department of Plant Pathology, University of California, Riverside 92521. Phytopathology 72:1235-1238. Accepted for publication 12 February 1982. Copyright 1982 The American Phytopathological Society. DOI: 10.1094/Phyto-72-1235.

The effects of moisture on the toxicity of methyl bromide (MB) and chloropicrin (CP) to the sclerotia of Sclerotium rolfsii and the microsclerotia of Verticillium albo-atrum were studied in a laboratory system in which the propagules were exposed to fixed concentrations of the toxicants in a free-flowing mixture in air for varying periods. Moist propagules exposed to the fumigants contained approximately 45% water and saturated propagules contained approximately 150% water, based upon oven-dry weights. The effectiveness of MB was not as greatly affected by the moisture content of the two propagules as that of CP. During short exposures, moist propagules were more sensitive than saturated propagules to MB. However, during long exposures, saturated propagules were more sensitive to the gas. In contrast to MB, the effectiveness of CP was greatly enhanced when the propagules were saturated. Saturated sclerotia of S. rolfsii were four to eight times more sensitive than moist sclerotia, depending upon time of exposure to CP. Saturated propagules of V. albo-atrum were 40 to 50 times more sensitive than moist propagules. The effect of mixtures of the two gases on saturated sclerotia of S. rolfsii was determined by holding MB concentrations constant at 10,200 μl/L and introducing various concentrations (175825 μl/L) of CP. The mixtures of MB and CP acted synergistically.