2017 ASHS Annual Conference

Chlorine, in the form of sodium hypochlorite, is applied to irrigation water for control of plant pathogens, biofilm and algae. The objective of this project was to identify the phytotoxicity threshold of container-grown Impatiens walleriana to chlorinated irrigation water. Impatiens walleriana plugs were transplanted to 6” containers. Plants were manually irrigated directly in the growing media, avoiding contact with the foliage, with known volume of solution containing 0, 2, 4, 8, 16 and 32 mg·L⁻¹ of free chlorine and zero leaching for four weeks. The experimental design was a complete randomized design with ten replicates per treatment and the experiment was conducted twice. Leaf chlorophyll content, visual injury and plant biomass were measured after 4 weeks. All plants treated with 8 mg·L⁻¹ of free chlorine or more exhibited all signs of of chlorine injury, including necrotic and chlorotic leaves, and reduced plant weight. Plants treated with 4 mg·L⁻¹ of free chlorine mostly exhibited reduced plant weight, but little to no necrosis and chlorosis. Chlorophyll content in plants treated with 16 and 32 mg·L⁻¹ of free chlorine was lower compared with plants treated with lower concentrations. The results indicate that Impatiens walleriana can be safely irrigated with water containg 2 mg·L⁻¹ of free chlorine. Results also suggest that phytotoxicity is not always visually noticeable and underlines the importance of defining phytotoxicity thresholds for other crops.