Control of waterborne microbes in irrigation: A review

Abstract

A wide range of plant pathogens have been identified in irrigation water sources and distribution systems. Algae and equipment-clogging biofilms also result from high microbial levels in irrigation water. The literature was reviewed on the effectiveness of water treatment options to control waterborne microbes. Water treatments included chemicals (chlorine, bromine, chlorine dioxide, ionized copper, copper salts, ionized silver, ozone, hydrogen peroxide, and peroxyacetic acid), non-chemical or physical treatments (filtration, heat, and ultraviolet radiation) and ecological alternatives (constructed wetlands, biosurfactants, and slow sand filtration). The objective was to summarize the effective dose for controlling target waterborne microorganisms. The effective dose for chemical water treatments to control plant pathogens was in some cases above documented phytotoxicity thresholds, and for most crops and technologies the phytotoxicity thresholds remain unknown. Most efficacy research has been conducted on chlorine (20 articles) or copper (18), but only 0–7 articles were found on other water treatments currently in use, indicating major knowledge gaps in treatment efficacy. Research is needed on control methods for algae and biofilms, in vivo pathogen studies, phytotoxicity thresholds, and the relationship between pathogen inoculum level and disease incidence in irrigation water. Finally, improved overall system design is required for risk management of waterborne microbes in irrigation, including a multiple barrier approach incorporating pre-filtration, multiple treatment stages, and monitoring of water quality.