Epidemiology of Pythium Root Rot of Mature Sugar Beets. P. von Bretzel, Research Associate, Department of Plant Pathology, University of Arizona, Tucson 85721. M. E. Stanghellini, and W. C. Kronland. Professor, and Research Assistant, Department of Plant Pathology, University of Arizona, Tucson 85721. Plant Dis. 72:707-709. Accepted for publication 3 April 1988. Copyright 1988 The American Phytopathological Society. DOI: 10.1094/PD-72-0707.

Root rot epidemics of mature sugar beets, caused by Pythium aphanidermatum, occurred during 1978 and 1979 in Arizona. In both years, approximately 70% of the plants were either dead or infected within 30 days after the onset of infection. A mortality rate of about 2% of the sugar beet population daily was calculated. Disease onset occurred about 9 mo after planting and coincided with the occurrence of soil temperatures of at least 27 C for 12 hr or more per day at the 10-cm soil depth. Adequate soil moisture, in addition to conducive soil temperatures, was required for a sustained epidemic of root rot.