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Ecology and Epidemiology

Reinvasion of Fumigated Soil by Fusarium oxysporum f. sp. melonis. J. J. Marois, Research plant pathologist, Soilborne Diseases Laboratory, Plant Protection Institute, Agricultural Research, Science and Education Administration, U.S. Department of Agriculture, Beltsville, MD 20705; M. T. Dunn(2), and G. C. Papavizas(3). (2)Department of Botany, University of Maryland, College Park 20742; (3)Research plant pathologist, Soilborne Diseases Laboratory, Plant Protection Institute, Agricultural Research, Science and Education Administration, U.S. Department of Agriculture, Beltsville, MD 20705. Phytopathology 73:680-684. Accepted for publication 17 November 1982. This article is in the public domain and not copyrightable. It may be freely reprinted with customary crediting of the source. The American Phytopathological Society, 1983. DOI: 10.1094/Phyto-73-680.

A field with a history of Fusarium wilt of muskmelon was fumigated with Vorlex (1,2-dichloropropane, 1,3-dichloropropene, and other related compounds plus methyl isothiocyanate) at 280 L/ha in 72-cm-wide beds and mulched with clear polyethylene. The pathogen was not detected 6 days after fumigation; however, by 32 days after fumigation, the pathogen was isolated consistently from the outer edges of the bed. Seventy-four days after fumigation there was a distinct pathogen population density gradient from the bottom 25 cm of soil to the top 5 cm of soil. By 102 days, the pathogen was distributed throughout the bed, similar to the nonfumigated beds. An experimental computer model was developed, which simulated the distribution of the pathogen propagules at weekly intervals after fumigation. The model indicated that the pathogen would spread more rapidly at depths of 15- 20 cm than at 0- 5 cm, and that an increase in depth and width of fumigated soil would be more effective in controlling pathogen recolonization than an increase in depth or width alone.