Submitted to: Plant Disease
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/21/2003
Publication Date: 2/1/2004
Citation: Copes, W.E., Chastaganer, G.A., Hummel, R.L. 2004. Activity of chlorine dioxide in a solution of ions and pH against Thielariopsis basicola and Fusarium oxysporum.. Plant Disease. 88:188-194. Interpretive Summary: Chlorine dioxide is a disinfestant that has potential for treating large quantities of irrigation water without damaging a wide array of ornamental plant species. This study was a continuation of previous work and showed interactions between pH, water hardness, and nutrient leachates would alter rates of chlorine dioxide required to achieve desired biocidal activity. Responses were similar for several types of spores of two fungi but rate ranges varied considerably. Rates needed to overcome these negative effects were determined. This information will lead to further studies and should be beneficial to other scientist, extension agents, ornamental plant producers, and any plant commodity group that will use chlorine dioxide.
Technical Abstract: Chlorine dioxide (ClO2) can be used to control pathogen propagules in irrigation water. To determine to what degree soluble inorganic ions and pH of water can interact to effect ClO2 activity, concentrations of ClO2 were mixed with equal concentrations (0 and 100 mg l-1) of nitrogen from ammonium, nitrogen from nitrate, and synthetic hard water (NsHW) and equal concentrations (0, 1, 3, and 5 mg l-1) of copper, iron, manganese, and zinc (CuFeMnZn) at pH levels 5 and 8. After 10 minutes of mixing, spores of Fusarium oxysporum and Chlara basicola were exposed to ClO2 doses for 30 seconds; then suspensions poured through filter paper disks. Disks were flushed with water and plated on 50% potato dextrose agar. Germination was quantified at 1 and 3 days. Water amendments significantly affected ClO2 activity similarly for all species, but the lethal dose of ClO2 resulting in 50% mortality (LD50) differed for F. oxysporum and C. basicola and by propagule type of C. basicola. The presence of divalent cationic micro-nutrients (CuFeMnZn) required higher doses of ClO2. With all other factors equal, LD50's were higher at pH 8 than at pH 5, except when CuFeMnZn was at 5 mg l-1 and NsHW was at 100 mg l-1. The differing response of pH was due to an interaction between CuFeMnZn, NsHW, and pH. The probit predicted rates of ClO2 needed to achieve a LD50 ranged from 0.5 - 7.0 mg l-1 for macro- and micro-conidia of F. oxysporum, 0.5 - 11.9 mg l-1 for conidia of C. basicola, and 15.0 - 45.5 mg l-1 for aleuriospores of C. basicola. CuFeMnZn and to a lesser degree pH and NsHW place a demand on ClO2 that required an increased dose of ClO2 to maintain comparable biocidal activity.