Control of Phytophthora capsici diseases in greenhouse squash by fast-flow filtration

Phytophthora spp. are challenging to manage in greenhouse production of ornamentals and vegetables when recirculating irrigation water is used. This study investigated the effectiveness of fast-flow filtration in controlling Phytophthora diseases in a model greenhouse vegetable system. Two greenhouse experiments were conducted to test the effect of filter media type (i.e., sand and iron-oxide-coated media [IOCM]), and application of the fungicide etridiazole in controlling P. capsici root and crown rot of acorn squash (Cucurbita pepo). Fast-flow filtration through the IOCM filter was more effective in controlling P. capsici than the sand filter. The plants in the IOCM filter and fungicide treatments did not display disease symptoms, whereas 44-100% of the plants in the sand filter treatment exhibited wilting and stunting symptoms. Squash plants in the IOCM treatment had chlorosis of older leaves and slight stunting due to nutrient deficiency. Plants treated with fungicide developed phytotoxicity symptoms that included chlorosis. In summary, plant pathogens such as Phytophthora spp. can be removed from irrigation water using fast-flow filtration through the IOCM, and this filtration method, combined with supplemental nutrient application, may be a promising alternative for disease management in vegetable greenhouses.