Sensitivity of Cercospora beticola populations in Turkey to flutriafol, mancozeb, and fentin acetate

The sensitivity of sugar beet leaf spot disease caused by Cercospora beticola to fungicides used in Turkey was determined using a mycelial growth assay in petri dishes with 100 fungal isolates. The isolates were obtained from samples collected from 6 sugar beet production areas in 2005 and 2006. Flutriafol, mancozeb, and fentin acetate were added to Aspergillus complete medium (ACM) at the rates of 0.0, 0.05, 0.1, 0.5, 1.0, 5.0, and 10.0 µg mL-1, and then mycelial growth was measured. ED50 values of flutriafol for all the isolates from the sugar beet production areas ranged from 0.04 to >10.0 µg mL-1. Tolerance to this fungicide was very high in 2 regions (Adapazari and Carsamba) where the disease is very prevalent due to climatic conditions. In these 2 areas 74.1%, 55.5%, 81.2%, and 68.7% of the isolates grew with 5 and 10 µg mL-1 of flutriafol, respectively (1 µg mL-1 flutriafol is considered inhibitory to the growth of the fungus). In the other 4 regions included in the study, tolerance was not as high. Tolerance to mancozeb developed in all the regions; however, the percentage of tolerant isolates was lowest in Carsamba (6%) and highest in Susurluk (47.3%). Tolerance to fentin acetate varied according to the criteria used for evaluation.