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Methyl Iodide, an Ozone-Safe Alternative to Methyl Bromide as a Soil Fumigant. H. D. Ohr, Department of Plant Pathology, University of California, Riverside 92521. N. M. Grech, Department of Plant Pathology; J. O. Becker, Department of Nematology; and M. E. McGiffen, Jr., Department of Botany and Plant Sciences, University of California, Riverside 92521. Plant Dis. 80:731-735. Accepted for publication 25 March 1996. Copyright 1996 The American Phytopathological Society. DOI: 10.1094/PD-80-0731.

Methyl iodide was tested as a possible replacement for methyl bromide as a soil fumigant due to the scheduled removal of methyl bromide from the market. Methyl iodide is a better methylating agent than methyl bromide; it is rapidly destroyed by UV light and therefore unlikely to be involved in stratospheric ozone depletion. In laboratory and field trials, we tested methyl iodide alone or in comparison with methyl bromide for effectiveness in controlling the fungi Phytophthora citricola, P. cinnamomi, P. parasitica, and Rhizoctonia solani; the nematode Heterodera schachtii; and the plants Abutilon theophrasti, Chenopodium album, C. murale. Convolvulus arvensis, Cyperus rotundus, Poa annua, Portulaca oleracea, and Sisymbrium irio. In addition, we compared methyl iodide for biocidal effectiveness with seven other alkyl iodides. In both laboratory and field trials, when compared at equivalent molar rates, methyl iodide was equal to or better than methyl bromide in controlling the tested soilborne plant pathogens and weeds. When compared with other alkyl iodides, methyl iodide was the most effective fumigant.