Control of Root Rot of Spinach Caused by Pythium aphanidermatum in a Recirculating Hydroponic System by Ultraviolet Irradiation. M. E. Stanghellini, Professor, Department of Plant Pathology, Environmental Research Laboratory, University of Arizona, Tucson 85721. L. J. Stowell, Research Associate, Department of Plant Pathology, and M. L. Bates, Research Assistant, Environmental Research Laboratory, University of Arizona, Tucson 85721. Plant Dis. 68:1075-1076. Accepted for publication 18 May 1984. Copyright 1984 The American Phytopathological Society. DOI: 10.1094/PD-68-1075.

Greenhouse recirculating hydroponic systems facilitate continuous dissemination of introduced plant pathogens. Trials were conducted to determine the efficacy of ultraviolet irradiation of infested water for control of root rot of spinach caused by Pythium aphanidermatum. Seventy-two 2-wk-old spinach seedlings were transplanted into separate hydroponic chambers, which received either recirculated ultraviolet-treated or untreated water from a common source. Water was infested with encysted zoospores and oospores and was recirculated at a flow rate of about 124 L/min through an ultraviolet disinfestation unit. Within 7 days of transplanting, all spinach seedlings were dead in the chamber receiving untreated water. No plant death or root infection occurred in the chamber receiving ultraviolet-treated water.