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Ecology and Epidemiology

Incidence-Severity Relationships for Common Maize Rust on Sweet Corn. H. R. Dillard, Department of Plant Pathology, New York State Agricultural Experiment Station, Cornell University, Geneva 14456; R. C. Seem, Department of Plant Pathology, New York State Agricultural Experiment Station, Cornell University, Geneva 14456. Phytopathology 80:842-846. Accepted for publication 14 March 1990. Copyright 1990 The American Phytopathological Society. DOI: 10.1094/Phyto-80-842.

Incidence and severity relationships for common maize rust on sweet corn were determined using the cultivar Jubilee grown in selected commercial fields in western New York State from 1986 through 1988. The relationships between incidence (percent diseased leaves) and severity (percent leaf area diseased or number of uredinia per leaf) were similar during the 3 yr of study. Incidence was under 80% when disease severity was 1?2% leaf area diseased and about six uredinia per leaf. Severity significantly increased after 80% incidence was reached. We propose the use of the 80% incidence parameter as an action threshold for initiation of fungicide applications prior to tasseling on the cultivar Jubilee to prevent development of damaging levels of disease.