Survey of Pythium and Phytophthora spp. in irrigation water used by Colorado commercial greenhouses

Abstract

The purpose of this study was to determine if irrigation water is a source of Pythium and Phytophthora spp. introduction into Colorado greenhouses. Nine greenhouses took part in the study; three each used municipal, well, or surface water as their irrigation supply. Water samples were collected from each greenhouse three times during Summer 1993. Samples were filtered, filter pads were incubated on selective media, and isolated pathogens were used to inoculate susceptible Cucumis sativus L. and Lupinus polyphyllus Findl. indicator plants. Pythium rostratum Butler and P. dissotocum Drechsler were isolated from surface water supplies. No Phytophthora was found in any water source. No differences were found in stem length or leaf number on inoculated versus control cucumbers or lupines. It was determined that both species of Pythium recovered are weak pathogens. Apparently, pathogenic Pythium and Phytophthora spp. are introduced into greenhouses in three counties in Colorado via means other than water supply.