Sensitivity of nursery plants to free chlorine in the management of plant pathogens in irrigation water
Recycled irrigation water risks spreading pathogens, which has prompted growers to chlorinate water, but there is no research assessing chlorine ability to kill common pathogens or the use of chlorine under nursery practices. The purpose of the present research was to (1) determine any phytotoxic responses and associated free chlorine thresholds of common nursery plants; (2) determine the free chlorine thresholds and their contact times required to kill five common pathogens; and (3) examine a free chlorine concentration in relation to safety for nursery plants and killing common pathogens at a commercial nursery. Above a certain threshold concentration, nursery plants exhibited signs of chlorine injury including necrosis and chlorosis. Results indicated that irrigation water containing free chlorine <2.5 mg·L -1 should not adversely affect the growth or appearance of nursery plants. The free chlorine threshold and critical contact time against ' Phytophthora infestans, Phytophthora cactorum, Pythium aphanidermatum, Fusarium oxysporum' and 'Rhizoctonia solani' were 1, 0.3, 2, 14 and 12 mg·L-1 for 3, 6, 3, 6 and 10 min, respectively. When recycled irrigation water was treated for 5 min with 2.4 mg·L -1 of free chlorine at a commercial nursery, results suggested that chlorine could be used to prevent the spread of common pathogens without losing market value of plants.