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Injection of Electrolytically Generated Chlorine into Citrus Microirrigation Systems for the Control of Certain Waterborne Root Pathogens. N. M. Grech, Graduate Student and Senior Research Pathologist, Citrus and Subtropical Fruit Research Institute, Nelspruit, 1200. F. H. J. Rijkenberg, Professor, Department of Microbiology and Plant Pathology, University of Natal, Pietermaritzburg. Plant Dis. 76:457-461. Accepted for publication 25 June 1991. Copyright 1992 The American Phytopathological Society. DOI: 10.1094/PD-76-0457.

Electrolytically generated chlorine was injected into citrus microirrigation systems. Propagules of Phytophthora nicotianae var. parasitica, P. citrophthora, Fusarium spp., algae, and slime-forming bacteria were killed. Nematodes were found to resist free-chlorine levels in water of up to 50 μg ml1. Microemitters delivering chlorinated water were less frequently blocked by bacterial and/or bacterial slime than those delivering unchlorinated water. Soil and root populations of Phytophthora and nematodes under citrus trees in the field were unaffected by chlorinated water. No chlorine-induced phytotoxicity was observed on field-grown plants. In glasshouse studies, treatment levels between 200 and 500 μg ml1 significantly reduced propagules of Phytophthora in the soil and, in some cases, eradicated the pathogen.

Keyword(s): pathogen control, water treatment.