VIEW ARTICLE

Ecology and Epidemiology

Determining Inoculum Potentials of Cylindrocladium floridanum in Cropped and Chemically-Treated Soils by a Quantitative Assay. J. A. Menge, Assistant Professor, Department of Plant Pathology, University of California, Riverside 92502; D. W. French, Professor, Department of Plant Pathology, University of Minnesota, St. Paul 55108. Phytopathology 66:862-867. Accepted for publication 13 January 1976. DOI: 10.1094/Phyto-66-862.

A quantitative assay was developed for determining inoculum potentials of Cylindrocladium floridanum in soil. Inoculum potentials were measured by determining the percentage of soil samples in a total of 100 1-g samples that produced signs of C. floridanum disease on alfalfa seedlings. Inoculum potentials of C. floridanum were directly correlated with percentages of diseased black spruce seedlings in four soils tested. Cylindrocladium floridanum survived for one growing season in field plots to which it was introduced regardless of soil type, cover crops, or chemical treatments. Three nonhost cover crops (oats, rye, and wheat) significantly increased the inoculum potential of C. floridanum during one growing season, whereas corn, soybeans, and buckwheat did not detectably alter inoculum potentials when compared to nontreated plots. No cover crop measureably altered the germination of microsclerotia of C. floridanum or numbers of soil microorganisms. Trichlorodinitrobenzene applied prior to soil infestation with C. floridanum reduced microsclerotial germination and inoculum potentials of C. floridanum. Methyl bromide, applied prior to infestation, resulted in increased inoculum potentials in a sandy soil and decreased inoculum potentials in a silt loam compared to inoculum potentials in nontreated plots.