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Comparative Toxicity of Gaseous Methyl Bromide to Ten Soilborne Phytopathogenic Fungi. Donald E. Munnecke, Professor, Department of Plant Pathology, University of California, Riverside, CA 92521; James L. Bricker(2), and Martin J. Kolbezen(3). (2)(3)Staff Research Associate, and Chemist, Department of Plant Pathology, University of California, Riverside, CA 92521. Phytopathology 68:1210-1216. Accepted for publication 26 January 1978. Copyright 1978 The American Phytopathological Society, 3340 Pilot Knob Road, St. Paul, MN 55121. All rights reserved.. DOI: 10.1094/Phyto-68-1210.

The fungi were exposed to six concentrations of methyl bromide (MB) in a free-flowing system and the LD90 values were calculated. Concentration and time for each LD90 value were plotted using log concentration vs. log time, and the resulting plots were linear. Slopes of the curves for such plots varied with each fungus. By comparing mean concentrations per hour required between 3 and 30 hr to obtain LD90 values, fungal sensitivities were: most sensitive, Phytophthora cinnamomi, P. citrophthora, P. parasitica, and Pythium ultimum; moderately sensitive, Armillaria mellea, Sclerotium rolfsii (mycelia), and Rhizoctonia solani; and least sensitive, Whetzelinia sclerotiorum (mycelia and sclerotia), S. rolfsii (sclerotia), Fusarium oxysporum (mycelia), and Verticillium albo-atrum (mycelia and microsclerotia). Sclerotia were more resistant to MB than were mycelia of the same fungus. The response of a given fungus growing in agar was nearly identical to the same fungus growing in roots. The concentrations and times necessary to kill the respective fungi are useful information for evaluating field fumigations.

Additional keywords: dosage response.