Common rust of sweet corn is caused by the fungus Puccinia sorghi. Epidemics of this disease can cause serious losses in yield and quality of sweet corn. High rust susceptibility of many popular sweet corn hybrids is a major factor contributing to rust epidemics. Another factor is that sweet corn is usually planted over an extended period from May through June for fresh and processing uses. The staggered planting schedules result in high concentrations of fungal spores in the air, originating from early planted fields, at the time when late-planted fields contain young actively growing susceptible plants.