Comparative Toxicity of Gaseous Methyl Bromide to Ten Soilborne Phytopathogenic Fungi

Abstract

The fungi were exposed to 6 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 h 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.