Vigor Response of Greenhouse Bell Pepper Due to Chlorine Dioxide Sanitized Irrigation Water

Recycling greenhouse irrigation water is becoming a popular practice due to water conservation efforts worldwide. However, water must be sanitized prior to recirculation to prevent contamination with plant pathogens. Chlorine dioxide (ClO₂), a common disinfectant used to treat municipal water and postharvest dump tanks, has been proposed as a disinfectant for recirculated irrigation systems.  Little research has been performed to determine if this chemical is appropriate to use for irrigation on greenhouse specialty crops. The objective of this study was to determine the effects of ClO₂ on the vigor of bell pepper plants grown in two different soilless medias (perlite and pine bark). Plants were transplanted in the University of Florida Protected Agriculture Project Greenhouse in Nov. Chlorine dioxide was added to the irrigation solution 11 days after transplanting at concentrations of 0, 10, 20 and 40 ppm. Relatively high concentrations were used to estimate an upper threshold for pepper tolerance to ClO₂. The experiment was repeated in March with reduced concentrations of ClO₂: 0, 2.5, 5 and 10 ppm. Chlorine dioxide is used at concentrations between 0.5 to 2 ppm for drinking-water sanitation, and concentrations in this range are also more practical for greenhouse use. Pepper plant height was measured weekly for six weeks. Leaf area, fresh mass, and dry mass of plants was measured at the end of six weeks. Data were analyzed using SAS (v.9.2). There was no interaction between media and ClO₂ concentration, therefore main effects are reported. For the concentrations examined, results indicate that increasing concentrations of ClO₂ in the irrigation water is negatively associated with plant height, leaf area, fresh mass and dry mass. For all parameters, peppers produced in perlite were less vigorous than peppers produced in pine bark.