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Reduction of Monilinia laxa Inoculum Potential in Almond Orchards Resulting from Dormant Benomyl Sprays. Donald C. Ramsdell, Research Assistant, Department of Plant Pathology, University of California, Davis 95616, Present address of senior author: Department of Botany and Plant Pathology, Michigan State University, East Lansing 48823; Joseph M. Ogawa, Professor, Department of Plant Pathology, University of California, Davis 95616. Phytopathology 63:830-836. Accepted for publication 28 December 1972. DOI: 10.1094/Phyto-63-830.

A presporodochial spray of proprietary benomyl 50W reduced numbers and size of sporodochia of Monilinia laxa to a greater extent than did 37% sodium pentachlorophenate (SPCP) but conidial release per unit size and percent germination were about equal. Mycelium was alive in the host tissue following benomyl treatment, but thin sections from these twigs showed fewer mycelial strands than in the untreated twigs where masses of mycelium were evident. Addition of oil to the benomyl spray enhanced sporodochial inhibition by providing longer residual action although the initial deposit was less. Oil increased penetration of benomyl into the bark and provided additional activity against the fungus. In shake cultures, the degradation product, methyl-2-benzimidazolecarbamate (MBC), but not benomyl, was concluded to be the chemical which inhibited mycelial growth and caused lysis of M. laxa mycelium. Benomyl and oil applied before sporodochial development controlled blossom blight equally as well as 37% SPCP in large-scale field trials using both high volume and concentrate spray applications. Applications of benomyl and oil made after sporodochial development provided less disease control than 37% SPCP, but more than 79% SPCP.

Additional keywords: sporodochial inhibition, brown rot.