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Control of Phytophthora Root Rot of Avocado with p-Dimethylaminobenzenediazo Sodium Sulfonate (Dexon). G. A. Zentmyer, Department of Plant Pathology, University of California, Riverside, California 92502; Phytopathology 63:267-272. Accepted for publication 30 August 1972. DOI: 10.1094/Phyto-63-267.

Dexon (p-Dimethylaminobenzenediazo sodium sulfonate) controlled Phytophthora root rot of avocado seedlings in the glasshouse when repeated applications were made. Control or reduction of disease severity was also obtained by repeated applications to large avocado trees in field plots. In artificially infested soil, the relationship between dosage of the chemical and amount of inoculum of the fungus was evident in terms of effect on disease severity and growth of seedlings. Dexon was fungistatic; Phytophthora cinnamomi survived exposure to 500 ppm of Dexon for up to 20 days, depending on the medium in which the fungus was growing. Dexon acted as an antisporulant; 5 ppm of the chemical reduced formation of sporangia and chlamydospores by 90-100%.