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The Chemical Control of Powdery Mildew by Fumigant Redistribution. Harvey W. Spurr, Jr., Research and Development Department, Union Carbide Corporation, Chemicals and Plastics, Agricultural Research Laboratory, Clayton, North Carolina 27520, Present address of senior author: Crops Research Division, ARS, USDA, Oxford Tobacco Research Station, Oxford, North Carolina 27565; E. L. Chancey, Research and Development Department, Union Carbide Corporation, Chemicals and Plastics, Agricultural Research Laboratory, Clayton, North Carolina 27520. Phytopathology 60:1062-1064. Accepted for publication 15 February 1970. DOI: 10.1094/Phyto-60-1062.

An experimental fungicide, 4-phenyl-4- (3-pyridyl)-3-oxatricyclo [4.2.1.0^{2, 5}] nonane (U.C. 23271), controls several foliar and soil-borne plant diseases and is an unusually effective eradicant of bean powdery mildew. Soil, stem, and leaf applications of U.C. 23271 resulted in insufficient systemic movement to eradicate mildew. A unique redistribution of U.C. 23271 resulting in mildew eradication was discovered. One hundred µg of U.C. 23271 localized on a small area of leaf surface completely eradicated powdery mildew over the entire leaf surface by fumigation. The long residual life of U.C. 23271, coupled with its excellent mildewcidal properties, suggests that its fumigant characteristics could have practical importance. Two structural analogues, diphenyl-3-pyridyl-methane and diphenyl-3-pyridyl-methanol, were mildew eradicants equivalent to U.C. 23271 in spray applications. The former was equivalent to U.C. 23271 as a fumigant and the latter was inactive. Thus, while the property of fumigant redistribution may have a practical significance, it alone does not explain the mildew eradication which was observed.