BASE-LINE SENSITIVITIES OF VENTURIA-INAEQUALIS TO STEROL DEMETHYLATION INHIBITORS

A set of monoconidial isolates of Venturia inaequalis representing a wild-type population was used to determine the baseline sensitivities and sensitivity distributions for several sterol demethylation inhibitors used in the control of apple scab. Baseline sensitivities expressed as ED50 values for growth of mycelia were 0.008-mu-g ml-1 (flusilazole), 0.03-mu-g ml-1 (penconazole and pyrifenox), 0.04-mu-g ml-1 (fenarimol), 0.05-mu-g ml-1 (bitertanol and tebuconazole), and 0.07-mu-g ml-1 (myclobutanil). The resistance factors calculated from ED50 values determined for a resistant baseline isolate of V. inaequalis were variable, ranging from 15 for flusilazole to 3 for pyrifenox.