The 2011 ASHS Annual Conference

Recirculating greenhouse irrigation is becoming a more common practice for vegetable growers in the US due to growing concern over freshwater shortages. Utilizing closed loop irrigation systems for greenhouse vegetable production not only saves the grower money due to reduced water and fertilizer use, it also reduces the amount of fertilizers being dispensed into the environment as spent irrigation. One drawback is that water-borne pathogens such as Pythium, Phytopthora, and Fusariam may proliferate in these irrigation systems. To prevent further spread of these pathogens irrigation is disinfected using chemical sanitizers such as chlorine, chlorine dioxide, ozone, and hydrogen peroxide. Chlorine dioxide is advantageous over other widely-used chemical sanitizers because it is active over a wide pH range, it has a high oxidation capacity, and compared to chlorine it doesn’t form carcinogenic halogenated compounds and is effective on organisms resistant to chlorine. Currently there is no recommendation for use of chlorine dioxide as a disinfectant in greenhouse vegetable production. To determine a rate recommendation for its use, two laboratory experiments were conducted at the University of Florida in Spring 2011. In the first experiment, nutrient solution prepared according to University of Florida fertilizer recommendations for greenhouse bell pepper was treated with two concentrations of chlorine dioxide (10 and 20 ppm), and the concentration of residual sanitizer was measured over an eight hour period. Well water containing no fertilizer was also treated with chlorine dioxide as a control to determine fertilizer influence on chlorine dioxide residual. In a second experiment, fertilizer solution inoculated with Pythium aphanidermatum was treated with 10 ppm chlorine dioxide and survival rate was confirmed over an hour long period by plating. In both experiments treatments were arranged in a randomized complete block design, replicated three times, and repeated. Regression analysis was used to describe both chlorine dioxide degradation in irrigation solution and Pythium survival rate in chlorine dioxide solution. These results are part of a larger set of experiments designed to develop a chlorine dioxide recommendation for sanitizing irrigation to prevent pathogen infection in closed loop systems in greenhouse bell pepper.