Control of Phytophthora Capsici Zoospores in Recycled Greenhouse Irrigation Water By Filtration.

Phytophthora capsici has been detected in surface water in the United States and elsewhere. Contaminated surface water used for crop irrigation has been a significant contributor to increased incidence of Phytophthora-infested vegetable fields and associated crop losses. Moreover, irrigation water recycling in greenhouses is becoming increasingly popular due to environmental and economic benefits, but this practice can exacerbate the spread of water mold pathogens. Therefore, water treatment is warranted to exclude pathogens from irrigation water and to prevent disease epidemics in greenhouses. This study investigated physical removal of P. capsici zoospores in recirculating irrigation water using small-scale ebb and flow irrigation and filtration systems packed with granular sand or iron oxide coated ceramic porous media. An additional fungicide treatment was also included for comparison. The performance of filtration and fungicide treatment in controlling pathogen infections of a P. capsici sensitive plant acorn squash (Cucurbita pepo) was evaluated by growing 12-day old squash seedlings in greenhouse nursery pots with peat potting mix for two or three weeks under irrigation of recirculating waters with and without P. capsici zoospore inoculation. The two-week and three-week trials were both concluded upon 100% plant death in the inoculated control treatment in the absence of filtration or fungicide. Foliar fresh weights of squash under iron oxide coated media and sand treatment were not different from that of non-inoculated control in the two-week trial (P < 0.05). In the three-week trial, however, foliar fresh weights of squash under filtration or fungicide application were significantly lower than that of non-inoculated control, and the iron oxide coated medium performed significantly better than the sand and fungicide application. Therefore, this preliminary work indicate that the filtration with iron oxide coated media is more effective in reducing the P. capsici infection than the sand filtration and fungicide application.