Submitted to: Southern Nursery Association Proceedings
Publication Type: Proceedings
Publication Acceptance Date: 8/15/2001
Publication Date: 2/15/2002
Citation: Copes, W.E., Chastagner, G.A., Hummel, R.L. 2002. Influence of Selected Inorganic Ions and PH on Fungicidal Activity of Chlorine Dioxide in Water. Southern Nursery Association Proceedings. 46:282-284.
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.