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Fungicide Movement in Soils. Charles S. Helling, Soil Scientist, ARS, USDA, Agricultural Research Center-West, Beltsville, Maryland 20705; D. Gayle Dennison(2), and Donald D. Kaufman(3). (2)(3)Microbiologists, ARS, USDA, Agricultural Research Center-West, Beltsville, Maryland 20705. Phytopathology 64:1091-1100. Accepted for publication 8 March 1974. DOI: 10.1094/Phyto-64-1091.

Bioassay methods, in combination with soil thin-layer chromatography (soil TLC), were developed to assess mobility of fungicides in soils. After leaching soil TLC plates with water, 10 soil fungi (Aspergillus fumigatus, Diplodia zeae, two isolates of Fusarium moniliforme, Fusarium roseum, Helminthosporium sativum, Penicillium chrysogenum, Penicillium rugulosum, Rhizoctonia solani, and Trichoderma viride), and an alga (Chlorella sorokiniana) were tested as visualizing agents by spraying plates with a liquefied nutrient agar suspension of the organism. Plates were incubated at 100% RH and approx. 28 C until zones of inhibition or stimulation appeared, usually in 1 to 4 days. The movement of 38 pesticides (33 fungicides, 3 insecticides, 1 acaricide, and 1 herbicide) in Hagerstown silty clay loam was determined. Relatively mobile compounds included: cycloheximide, cycloheximide oxime, Ceresan L (the mercaptide component), Dexon, formetanate, formparanate, and oxycarboxin. Immobile compounds included chloranil, chloroneb, DCNA, dichlone, dodine, hexachlorophene, Morestan, PCNB, TCNA, Terrazole, and zineb. T. viride and C. sorokiniana were the two organisms sensitive to the greatest number of fungicides. The mobility order nabam > maneb > zineb was confirmed by bioassay and autoradiography. In five soils, movement of these [14C]dithiocarbamate fungicides was inversely related to soil organic matter content.

Additional keywords: fungicide diffusion, organic mercurial fungicides, dithiocarbamate fungicides.