Reductions of Pythium ultimum, Thielaviopsis basicola, and Macrophomina phaseolina Populations in Soil Associated with Ammonia Generated from Urea. D. Chun, Graduate Research Assistant, Department of Botany and Plant Pathology, Michigan State University, East Lansing 48824-1312. J. L. Lockwood, Professor, Department of Botany and Plant Pathology, Michigan State University, East Lansing 48824-1312. Plant Dis. 69:154-158. Accepted for publication 6 August 1984. Copyright 1985 The American Phytopathological Society. DOI: 10.1094/PD-69-154.

Sandy loam soil infested with Pythium ultimum, Thielaviopsis basicola, and Macrophomina phaseolina was amended with urea at concentrations of 0.1, 0.25, 0.5, and 1.0 (w/w) in field microplots. Ammonia concentrations increased with the amount of urea applied. Population densities of all three pathogens were significantly and often markedly decreased by urea concentrations of 1.0, 0.5, and 0.25%; 0.1% urea appeared to be effective in reducing soil populations after 31 days at high soil temperatures but was ineffective even after 34 days at low soil temperatures.

Keyword(s): soil amendments, soilborne pathogens.