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Oxamyl-Treated Soil Protects Tobacco Against Black Shank. P. M. Miller, Plant Pathologist, The Connecticut Agricultural Experiment Station, New Haven 06504; John L. McIntyre, Assistant Plant Pathologist, The Connecticut Agricultural Experiment Station, New Haven 06504. Phytopathology 66:221-224. Accepted for publication 16 August 1975. DOI: 10.1094/Phyto-66-221.

Oxamyl (methyl Ní , Ní-dimethyl-N[(methylcarbamoyl) oxy]-1-thiooxamimidate) at rates of 5.58, 11.16, and 22.32 kg active ingredient (a.i.)/hectare (= 1, 2, and 4 lb a.i./acre, respectively) was applied to field plots of sandy loam, pH 5.5, in May. Soil samples were removed to the greenhouse at 30-day intervals over a 4-month period, planted with tobacco Windsor Shade 117 (WS 117), and inoculated 1 week later with approximately 104 zoospores of a Connecticut isolate of Phytophthora parasitica var. nicotianae. Seedlings of WS 117 tobacco transplanted into soils that were treated up to 90 days earlier with 22.32 kg (a.i.) oxamyl/hectare did not develop black shank symptoms, while 11.16 kg (a.i.)/hectare gave intermediate protection and 5.58 kg (a.i.)/hectare afforded no protection over this time period. Results from greenhouse studies indicated that a 2-week period is required after soil is treated with oxamyl before seedlings are protected against the pathogen. Tobacco seedlings grown up to 21 days in oxamyl-treated soil and then transplanted into nontreated soil for 1 week prior to inoculation developed black shank symptoms. In vitro studies showed that oxamyl concentrations as high as 100 µg active ingredient/ml (= 548.34 kg active ingredient/hectare) are not fungicidal or inhibitory to zoosporangia production. Results suggest that protection against black shank is due to breakdown products of oxamyl.

Additional keywords: nematicide, soil-borne pathogen.