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Epiphytotics of Maize Dwarf Mosaic and Maize Chlorotic Dwarf Diseases in Ohio. Raymond Louie, Research Plant Pathologist, Department of Plant Pathology, Ohio Agricultural Research and Development Center, Wooster 44691; J. K. Knoke(2), and D. T. Gordon(3). (2)(3)Research Entomologist, Department of Entomology, North Central Region, ARS, USDA, and Associate Professor, Department of Plant Pathology, respectively, Ohio Agricultural Research and Development Center, Wooster 44691. Phytopathology 64:1455-1459. Accepted for publication 11 June 1974. DOI: 10.1094/Phyto-64-1455.

Maize dwarf mosaic (MDM) and maize chlorotic dwarf (MCD) epiphytotics were studied in southern Ohio, where these diseases occur naturally. Successively-planted field plots and 14-day-old corn plants (trap plants), exposed to field conditions for weekly intervals throughout the season, were used to monitor the development of the epiphytotics. Diagnostic symptoms of MDM included mosaic, fleck, and ring patterns; a veinbanding symptom was diagnostic for MCD. Delayed development of MDM and MCD epiphytotics was associated with early field plantings. Both MDM and MCD epiphytotics began in early June. The incidence of MDM subsequently increased and remained high throughout the season. MCD incidence increased to a peak in mid-July, then sharply declined. The potential occurrence of each disease was measured more accurately with trap plants than with successive field plantings.