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Characterizing Fenbuconazole and Propiconazole Sensitivity and Prevalence of ‘Mona’ in Isolates of Monilinia fructicola from New York

July 2011 , Volume 95 , Number  7
Pages  828 - 834

Sara M. Villani and Kerik D. Cox, Department of Plant Pathology and Plant-Microbe Biology, New York State Agricultural Experiment Station, Cornell University, Geneva, NY 14456

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Accepted for publication 2 March 2011.

Demethylation inhibitor (DMI) resistant populations of Monilinia fructicola, the causal agent of brown rot of stone fruit, and the presence of the genetic DMI resistance determinant ‘Mona’ have been reported throughout the eastern United States. In this study, we endeavored to conduct a comprehensive investigation of DMI sensitivity, the prevalence of ‘Mona’, and implications of DMI use for M. fructicola populations from New York and Pennsylvania. Of the 18 orchards surveyed, only 9 were primarily composed of isolates with either resistance or reduced sensitivity to fenbuconazole and propiconazole. The DMI resistance determinant ‘Mona’ was only found in 5 orchards, present in isolates with a range of sensitivity phenotypes, and not always present in resistant isolates. These results suggested that ‘Mona’ only contributes to a portion of the quantitative resistance response to DMI fungicides. On detached blossoms and fruit, protective applications of fenbuconazole (Indar 2F) against isolates with resistance or reduced sensitivity resulted in significantly (P < 0.05) lower brown rot incidence compared to applications of propiconazole (Orbit 3.6EC) and water controls. By comparison, therapeutic applications of fenbuconazole and propiconazole against isolates with resistance or reduced sensitivity provided little to no reduction in brown rot incidence on blossoms and fruit.

© 2011 The American Phytopathological Society