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Dosage Response of Phytophthora cinnamomi to Methyl Bromide. Donald E. Munnecke, Professor of Plant Pathology, Department of Plant Pathology, University of California, Riverside 92502; James L. Bricker(2), and M. J. Kolbezen(3). (2)(3)Staff Research Associate III, and Chemist, respectively, Department of Plant Pathology, University of California, Riverside 92502. Phytopathology 64:1007-1009. Accepted for publication 21 February 1974. DOI: 10.1094/Phyto-64-1007.

Dosage responses of P. cinnamomi to methyl bromide (MB) were determined in 48 experiments by fumigating the fungus in a free-flowing system at concns from 4,000 to 38,700 µliters/liter (vol) for exposure times 1-46 h. The various LD90 values were linearly correlated by plotting the log concn (µliters/liter) vs. log time (h). In this way concn × time products (CT) for all LD90 values, within limits, were obtained. The slopes of the CT regression lines obtained for P. cinnamomi growing on agar, in living roots, or existing as chlamydospores in soil were almost identical, indicating that the response of P. cinnamomi to MB was uniform, regardless of the type of test material used. Analysis of the three CT curves indicated that chlamydospores were the most sensitive to MB.