Efficacy of chlorine, chlorine dioxide and ultraviolet radiation as disinfectants against plant pathogens in irrigation water
A number of disinfection treatments are available to treat irrigation water to reduce the risk of plant disease. However, limited published studies had compared the efficacy of disinfection treatments on a range of plant pathogen species, on their various life stages and in different water qualities. In this study, propagules (spores, mycelium, cells) of eight plant pathogens including Clavibacter michiganensis subsp. michiganensis, Alternaria alternata, Chalara elegans, Colletotrichum gloeosporioides, Calonectria pauciramosa, Fusarium oxysporum, Phytophthora cinnamomi and Pythium aphanidermatum were exposed to chlorine (sodium hypochlorite), chlorine dioxide and ultraviolet radiation (UV) at a range of application rates and exposure times, in deionised water and dam water. The efficacy of treatments varied with exposure time, application rate, water type and the pathogen and propagule. Cl. michiganensis subsp. michiganensis, Ph. cinnamomi and Py. aphanidermatum propagules were most sensitive to all treatments, while propagules of Ch. elegans, Ca. pauciramosa and F. oxysporum required the highest rates and longest exposure times to chlorine, chlorine dioxide and UV to kill >99 % CFUs. Chlorine dioxide, applied as a Bshock^ treatment at a high rate for a limited time period, and UVradiation offered more effective biocidal activity than the chlorine levels tested in both water types. This study demonstrates that sensitivity to disinfection treatments and application rates varies between pathogens, and between propagules of the same pathogen.