QoI Resistance in Fusicladium carpophilum Populations from Almond in California and Evaluation of Molecular Resistance Mechanisms

Disease management failures have been reported in California for almond scab caused by Fusicladium carpophilum following quinone outside inhibitor (QoI) applications. Resistance in the pathogen populations was found to be common and at high incidence in the major almond-growing regions beginning in 2003, 4 years after registration of azoxystrobin on this crop. Two levels of azoxystrobin resistance, moderate and high, were identified with 50% effective concentration (EC ) values between 0.15 and 10 μg/ml or >40 μg/ml, respectively. Reference isolates collected before resistance was detected had EC values