Area of impact: Leaves
Description: Round red to dark brown pustules, found on leaf surfaces. Rust spores are cinnamon brown. In severe cases, leaf death can occur.
Pathogen involved: Puccinia sorghi (a fungus)
Timing/Conditions: Spores are introduced early to midsummer. Pustules are more common after silking. Common rust needs about six hours of moisture to germinate; it prefers cool temperatures, heavy dew and high relative humidity. Young leaves are most likely to be infected.
Contributing factors: Overwinters in the southern U.S. and Mexico and blows north on the wind into the Corn Belt in early summer.
Management practices: Use resistant hybrids and apply fungicides early when pustules are few.