Shift of Monilinia spp. and Distribution of Isolates Sensitive and Resistant to Benomyl in California Prune and Apricot Orchards. Themis J. Michailides, Postdoctoral Research Associate VI, Department of Plant Pathology, University of California, Davis 95616. Joseph M. Ogawa, and Dan C. Opgenorth. Professor, Department of Plant Pathology, University of California, Davis 95616, and Associate Plant Pathologist, California Department of Food and Agriculture, Sacramento 95814. Plant Dis. 71:893-896. Accepted for publication 10 June 1987. Copyright 1987 The American Phytopathological Society. DOI: 10.1094/PD-71-0893.

Monilinia fructicola and M. laxa are the causal agents of brown rot blossom and twig blights and fruit rot of prunes (Prunus domestica) and apricots (P. armeniaca) in California. In contrast to 1974, M. fructicola was more commonly isolated than M. laxa from diseased prunes and apricots in 1982 and 1983. All isolates of M. laxa were sensitive to benomyl. Isolates of M. fructicola resistant to 1 µg/ml benomyl were detected in prune orchards in 10 of 12 counties surveyed and in apricot orchards in all six counties surveyed. In addition, in three counties, M. fructicola isolates resistant to 4 µg/ml benomyl were found in both prune and apricot orchards. Reasons for the shift in Monilinia spp. are discussed.