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Disease Progress and Yield Loss in Aphanomyces Root Rot of Peas. W. F. Pfender, Research associate, Department of Plant Pathology, University of Wisconsin, Madison 53706; D. J. Hagedorn, professor, Department of Plant Pathology, University of Wisconsin, Madison 53706. Phytopathology 73:1109-1113. Accepted for publication 10 February 1983. Copyright 1983 The American Phytopathological Society. DOI: 10.1094/Phyto-73-1109.

The epidemiology of Aphanomyces root rot of pea was studied in field plots on sandy soil. We found that the pathogen, Aphanomyces euteiches f. sp. pisi, can spread from an infected plant to a limited number of neighboring plants in the pea stand. In small field plots with soil infested at various inoculum levels, the disease incidence (percentage of plants infected) increased rapidly early in the season at high inoculum levels; at lower inoculum levels, the increase in disease incidence was similarly rapid, but occurred later in the season. Yield varied inversely with logarithm of soil inoculum level. The inoculum level of A. euteiches f. sp. pisi in soil decreased about 50% per year in the absence of a pea crop.