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Control of Sunflower Downy Mildew with Metalaxyl. J. M. Melero-Vara, Research Plant Pathologist, Departmento Oleaginosas y Plantas de Gran Cultivo, C.R.I.D.A.-10, Apdo. 240, Córdoba, Spain. C. Garcia-Baudin, Research Assistant, C. J. Lopez-Herrera, Graduate Research Assistant, Departamento Oleaginosas y Plantas de Gran Cultivo, C.R.I.D.A.-10, Apdo. 240, Córdoba, Spain; and R. M. Jimenez-Diaz, Professor, Departamento Patología Vegetal, Universidad de Córdoba, Apdo. 246, Córdoba. Plant Dis. 66:132-135. Accepted for publication 12 May 1981. This article is in the public domain and not copyrightable. It may be freely reprinted with customary crediting of the source. The American Phytopathological Society, 1982. DOI: 10.1094/PD-66-132.

Dressing of sunflower seeds with metalaxyl at 1, 2, or 4 g a.i./kg prevented Plasmopara helianthi sporulation on seedlings inoculated by dipping the roots into a zoosporangial suspension. Washing seedlings with water before inoculation did not influence results, suggesting a systemic activity of the fungicide in the seedlings. One or two drenches of soil in pots with metalaxyl at concentrations of 125, 250, or 500 mg a.i./L reduced symptom severity in P. helianthi-infected seedlings and allowed plants to resume normal growth. Symptom remission in infected plants was also achieved by fungicide sprays in the field. Highest incidence of symptom remission occurred with three sprays at a concentration of 520 mg a.i./L and two or three sprays at a concentration of 1,040 mg a.i./L.