Protective, Curative, and Eradicant Activity of Difenoconazole Against Venturia inaequalis, Cercospora arachidicola, and Alternaria solani. H. Dahmen, CIBA-GEIGY Ltd., Agricultural Division, CH-4002 Basel, Switzerland. T. Staub, CIBA-GEIGY Ltd., Agricultural Division, CH-4002 Basel, Switzerland. Plant Dis. 76:774-777. Accepted for publication 9 January 1992. Copyright 1992 The American Phytopathological Society. DOI: 10.1094/PD-76-0774.

The protective and curative activities of difenoconazole against Venturia inaequalis, Cercospora arachidicola, and Alternaria solani were determined in the greenhouse on apple, peanut, and tomato, respectively. In addition, the effects of difenoconazole on established, visible scab lesions and on the production of spores from treated lesions were evaluated. Spray treatments with 12.5 μg a.i/ml of difenoconazole provided 90 and 100% disease control of V. inaequalis following 3 days of protective and 3 days of curative treatments, respectively. Applications 5 or 7 days after inoculation were too late to prevent symptom appearance, but they prevented sporulation. Against C. arachidicola, difenoconazole showed excellent protective and curative activity. The protective activity persisted for up to 21 days. Curative application with 75 ?g a.i./ml of difenoconazole provided 89–100% disease control and 90–100% antisporulant activity. Eradicative treatments with 75 μg a.i./ml provided at least 80% antisporulant activity. In the few lesions that developed after protective treatments with the longest application intervals and lowest concentration, the compound had little antisporulant activity. Against V. inaequalis, with treatments 3 days prior to inoculation and a concentration of 12.5 μg a.i./ml, only 63% antisporulant activity was found. Against C. arachidicola difenoconazole worked similar to chlorothalonil, which was included as a standard. Treatment 21 days prior to inoculation with 250 ?g a.i./ml of difenoconazole and 1,250 μg a.i./ml of chlorothalonil gave 80% disease control but almost no reduction in sporulation. Against A. solani the protective and curative activity of difenoconazole was superior to that of mancozeb. Treatments 7 days prior to and 1 day after inoculation gave 83–100% disease control. Eradicative treatments applied 2 days after inoculation provided little initial control, but 10 days after inoculation they provided about 60% control. Difenoconazole is the first sterol inhibitor compound with excellent activity against A. solani. These results have an important bearing on optimal treatment schedules and the selection of suitable mixture partners for difenoconazole.