Efficacy of Chlorine in Controlling Five Common Plant Pathogens

Recycled irrigation water is one of the major sources of inoculum and may spread plant pathogens throughout the nursery or greenhouse operation. Chlorination is the most economical method of disinfecting water and has been adopted by some North American commercial growers. However, chlorine has not been assessed as a disinfectant for the common plant pathogens Phytophthora infestans , Phytophthora cactorum , Pythium aphanidermatum , Fusarium oxysporum , and Rhizoctonia solani . These pathogens were exposed to five different initially free chlorine solution concentrations ranging from 0.3 to 14 mg·L −1 in combination with five contact times of 0.5, 1.5, 3, 6, and 10 min to determine the free chlorine threshold and critical contact time required to kill each pathogen. Results indicated that the free chlorine threshold and critical contact time for control of P. infestans , P. cactorum , P. aphanidermatum , F. oxysporum , and R. solani were 1, 0.3, 2, 14, and 12 mg·L −1 for 3, 6, 3, 6, and 10 min, respectively.