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Disease Control and Pest Management

Some Biocidal Properties of 1, 3-D and its Degradation Product. R. C. Baines, Nematologist Emeritus, Department of Nematology, University of California, Riverside, CA 92502; L. J. Klotz(2), and T. A. DeWolfe(3). (2)(3)Professor of Plant Pathology and Plant Pathologist Emeritus, and Plant Pathology Specialist (ret.) Department of Plant Pathology, University of California, Riverside, CA 92502. Phytopathology 67:936-940. Accepted for publication 7 January 1977. Copyright 1977 The American Phytopathological Society, 3340 Pilot Knob Road, St. Paul, MN 55121. All rights reserved.. DOI: 10.1094/Phyto-67-936.

The toxicity of fumigant residues to sweet orange seedlings planted in a moist sandy loam soil 80 days after treatment with 62.4, 125, 250 μg/g of 1, 3-dichloropropene (1, 3-D) was shown to be due mainly to chloroallyl alcohol, a degradation product of 1, 3-D. When 31.2 μg/g of 1, 3-D was applied in nonsterilized soil, the chloroallyl alcohol formed was biologically degraded and was not toxic to sweet orange seedlings. However, concentrations of 62.4-250 μg/g 1, 3-D in soil interfered with the biological degradation of chloroallyl alcohol, and the fumigant residue was highly toxic to sweet orange seedlings planted 80 days after treatment. Likewise in steam-sterilized soil treated with concentrations of 31.2-250 μg/g of 1, 3-D or 40-320 μg/g of chloroallyl alcohol the residues were highly toxic to sweet orange seedlings 80 days after treatment. The 1, 3-D was more toxic to citrus nematodes and to Phytophthora parasitica than to organisms that biodegrade chloroallyl alcohol. Concentrations of 4.6 and 5.6 μg/g of 1, 3-D in a sandy loam soil were lethal to 100% of the second-stage citrus nematode larvae, and 37.2 μg/g was lethal to 100% of the P. parasitica propagules. A concentration of 40 μg/g of chloroallyl alcohol in soil was lethal to 91% of the citrus nematodes. Colonies of P. parasitica, 2 mm in diameter, were not killed after 48 hr of exposure to 1,000 μg/ml of chloroallyl alcohol, the strongest concentration tested, but new growth at the surface of the colonies was negligible (indicating a fungistatic effect) in 400-1,000 μg/ml. These data indicate that the formation of chloroallyl alcohol by hydrolysis of 1, 3-D in soil does not improve control of the citrus nematode nor of P. parasitica, and, that phytotoxic concentrations of chloroallyl alcohol may occur when high concentrations of 1, 3-D are applied.

Additional keywords: phytotoxicity of 1, 3-D and of chloroallyl alcohol.