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  • Author or Editor: Laura Pickett Pottorff x
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With the cooperation of six commercial greenhouses (five in Colorado, one out of state), rooted poinsettia cuttings and bedding plant plugs were collected and analyzed for Pythium and Rhizoctonia, two common root rotting pathogens in Colorado greenhouses. Samples of plant, soil, and water debris were taken from four greenhouses, as well as samples of growing media ready for use. These were also analyzed for Pythium and Rhizoctonia. Fungi recovered from the plant, debris, or growing media samples were identified, grown in pure culture, and introduced into susceptible plants (Vinca minor) in pathogenicity studies. Neither pathogen was isolated from the rooted poinsettia cuttings tested. Pythium was not found in any of the plug material or in growing media. Rhizoctonia solani was found in 16% of the plug samples and 7% of the growing media samples tested. Debris from greenhouse floors yielded four species of Pythium as well as Rhizoctonia solani. Isolates of each fungus were able to colonize, but not adversely affect, inoculated plants in pathogenicity studies. It appears that disease causing organisms that have potential to decrease plant quality and growth are already present in the greenhouse. Control of root rotting pathogens can best be carried out by relying heavily on sanitation measures.

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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.

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Crops grown in high tunnels are just as susceptible to pests and diseases as those grown under greenhouse and field conditions. Crops that lend themselves economically to this type of production system are edible and/or minor crops. Therefore, labeled pesticides for these crops are limited and sometimes nonexistent. However, there is a wide range of integrated pest management (IPM) strategies available to high tunnel producers. These strategies include biological control, which is often left out of traditional IPM programs when labeled pesticides are available. High tunnel production is very conducive to the inclusion of biological controls and allows for a truly IPM system. This article provides a selective overview of common arthropod pests and diseases encountered in high tunnels, as well as strategies that have potential for becoming best management practices in high tunnels with additional research.

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