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Disease Control and Pest Management

Control of Pythium Blight on Bean with Ethazol and Prothiocarb. G. C. Papavizas, Soilborne Diseases Laboratory, Plant Protection Institute, Agricultural Research Service, U.S. Department of Agriculture, Beltsville, MD 20705; J. A. Lewis(2), R. D. Lumsden(3), P. B. Adams(4), W. A. Ayers(5), and J. G. Kantzes(6). (2)(3)(4)(5)Soilborne Diseases Laboratory, Plant Protection Institute, Agricultural Research Service, U.S. Department of Agriculture, Beltsville, MD 20705; and (6)Department of Botany, University of Maryland, College Park, MD 20742. Phytopathology 67:1293-1299. Accepted for publication 29 March 1977. Copyright © 1977 The American Phytopathological Society, 3340 Pilot Knob Road, St. Paul, MN 55121. All rights reserved.. DOI: 10.1094/Phyto-67-1293.

In vitro toxicity of the experimental systemic fungicide, N-(3-dimethylaminopropyl) thiocarbamic acid S-ethylester hydrochloride [DTEH, SN41703, prothiocarb (proposed)] against 11 Pythium spp. was quite uniform; the dosage response curves were linear and generally steep up to 1.0-2.0 μg active ingredient (a.i.)/ml, with ED₅₀ values ranging from 0.1 to 1.0 μg/ml. When ED₁₀₀ values were considered, P. irregulare, P. butleri, P. arrhenomanes, P. debaryanum, and P. myriotylum, in the order given, were the most sensitive species. The in vitro effectiveness of DTEH was pH-dependent, with the best suppression obtained at about pH 6.2 - 7.4. The efficacy of ethazol, DTEH, and a DTEH analog [propyl-N-(γ-dimethylaminopropyl) carbamate (SN39744, PDAC)] were compared as seed treatments with other fungicides in the greenhouse against damping-off and Pythium blight of bean caused by P. aphanidermatum, P. myriotylum, and P. ultimum. Only the systemic fungicide DTEH completely prevented Pythium damping-off and blight when applied directly to the seed. It also was completely effective when applied to the seed by solvent infusion with water or ethanol as the solvent. With ethazol, the best control of damping-off and blight was obtained when the fungicide was applied to the seed with acetone or di-chloromethane as solvents. The organic solvents alone neither increased nor reduced Pythium blight and seed germinability. The only fungicide applied to the seed that reduced Pythium blight and resulted in significant yield increases in a heavily infested field near Salisbury, Maryland was DTEH.