Efficacy of Nonionic Surfactants in the Control of Zoospore Spread of Pythium aphanidermatum in a Recirculating Hydroponic System. M. E. Stanghellini, Department of Plant Pathology, University of Arizona, Tucson 85721. S. L. Rasmussen, D. H. Kim, and P. A. Rorabaugh, Department of Plant Pathology, University of Arizona, Tucson 85721. Plant Dis. 80:422. Accepted for publication 1 February 1996. Copyright 1996 The American Phytopathological Society. DOI: 10.1094/PD-80-0422.

Zoosporic fungi are among the most destructive root pathogens in recirculating hydroponic cultural systems, and zoospores have been implicated as the primary, if not sole, infectious propagule responsible for the spread of these pathogens via the recirculating nutrient solution. In vivo experiments employing cucumbers as the susceptible host and Pythium aphanidermatum as the root pathogen demonstrated the efficacy of surfactants in the control of root disease caused by this fungus. Amending the recirculating nutrient solution with a nonionic surfactant (final concentration, 20 mg a.i./ml) resulted in complete control of the spread of the fungus via the recirculating nutrient solution. Zoospores were identified as the sole propagule responsible for pathogen dissemination in the recirculating nutrient solution. In the absence of a surfactant, all plants within a recirculating hydroponic unit were killed within 5 to 6 weeks following hypocotyl inoculation of a single plant in the hydroponic unit.