Protective, Curative and Eradicant Activity of the Strobilurin Fungicide Azoxystrobin against Cercospora beticola and Erysiphe betae

Abstract The protective, curative and eradicant activity of the strobilurin fungicide azoxystrobin against Cercospora beticola and Erysiphe betae on sugar beet was determined under growth chamber conditions. Difenoconazole and chlorothalonil were used as standard fungicides against C. beticola, while chlorothalonil was replaced by sulphur against E. betae. Fungicides were applied before (protective treatments) and after (curative treatments) inoculation at 24, 48 and 96 h intervals, respectively. An additional spray treatment was applied after the appearance of the symptoms to evaluate the eradicant activity of the fungicides tested. Applications of azoxystrobin at 16 μ/ml provided 89–94% and 95–97% disease control against C. beticola and E. betae, respectively. Curative treatments of azoxystrobin either at 8 or 16 μg/ml provided control of Cercospora leaf‐spot higher than 90% only when it was applied 24 h after inoculation of the plants. Comparatively, chlorothalonil (100 μg/ml) provided satisfactory control of C. beticola when applied in protective treatments (83–87% disease control) but showed little activity when applied after the inoculation of the seedlings (45–76% disease control). High control efficacy against E. betae was also obtained by protective applications of sulphur (600 μg/ml) but the fungicide failed to provide satisfactory disease control, particularly when applied for 48 or 96 h after inoculation of seedlings. Difenoconazole (8 μg/ml) gave excellent protective and curative activity against both pathogens. Eradicative treatments with azoxystrobin provided high antisporulant activity of 94–96% and 85–93% against C. beticola and E. betae, respectively. Similarly, high antisporulant activity was also provided by difenoconazole, while postsymptom applications of chlorothalonil and sulphur provided significantly lower antisporulant activity against C. beticola and E. betae, respectively. Such results encourage the evaluation of azoxystrobin under field conditions to determine optimal treatment schedules and to select possibly partner fungicides for use in mixtures.