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Inhibition of Mycelial Growth of Monilinia Species and Suppression and Control of Brown Rot Blossom Blight of Almond with Iprodione and E-0858. J. M. OSORIO, Former Graduate Student, Department of Plant Pathology, University of California, Davis 95616. J. E. ADASKAVEG, Research Plant Pathologist, and J. M. OGAWA, Professor, Department of Plant Pathology, University of California, Davis 95616. Plant Dis. 78:712-716. Accepted for publication 24 March 1994. Copyright 1994 The American Phytopathological Society. DOI: 10.1094/PD-78-0712.

The fungicide iprodione and the heterocyclic anilide E-0858 were compared with benomyl for in vitro inhibition of mycelial growth of Monilinia laxa and M. fruclicola, for suppression of anther infection of blossoms in the laboratory, and for control of brown rot blossom and twig blight in the field. All 100 isolates of M. laxa obtained from an orchard in Solano County, California, were sensitive to benomyl (no growth at 1.0 μg a.i./ml), whereas all 100 isolates from an orchard in Fresno County, California, were resistant to benomyl (growth at 1.0 μg a.i./ml). Effective concentrations (EC50) of benomyl in Czapek's medium for inhibition of mycelial growth of M. laxa or M. fruclicola averaged 0.09 ?g/m\ for sensitive isolates and 0.77 μg/ ml for resistant isolates. Both iprodione and E-0858 were active against benomyl-sensitive and benomyl-resistant isolates of M. laxa and M. fructicola. Iprodione incorporated into PDA or Czapek's medium was inhibitory to both M. laxa and M. fructicola, with EC50 values between 0.52 and 0.75 μg a.i./ml. EC50 values of E-0858 incorporated in Czapek's medium were 0.30-0.36 μg a.i./ml for M. laxa and 0.89-0.98 μg a.i./ml for M. fruclicola, whereas EC50 values of E-0858 in potato-dextrose agar were >450 μg a.i./ml for inhibition of either M. laxa or M. fruclicola mycclia. In laboratory studies, anther infection was suppressed when open blossoms were sprayed with E-0858 or iprodione within 24 hr after inoculation with a benomyl-sensitive isolate of M. laxa. In field studies conducted in almond orchards with benomyl-sensitive or benomyl-resistant populations of M. laxa, applications of E-0858 or iprodione at pink bud (closed blossoms) and full bloom (opened blossoms) effectively reduced brown rot twig blight. Mycelial inhibition and suppression of disease development contribute to the high efficacy of iprodione and E-0858 in control of brown rot blossom and twig blight of almond.

Keyword(s): benzimidazoles, dicarboximides, Prunus dulcis, pyridines