Common Rust

Puccinia sorghi

Common rust infection on a corn leaf
Common rust infection on a corn leaf. Photo courtesy of Daren Mueller. Licensed under CC BY 3.0.
Common rust is a fungal disease of corn. It thrives under cool, humid conditions. It causes the most damage to younger corn and hence is particularly severe in late-planted corn.
Common rust is characterized by small brown lesions. Unlike southern rust, the lesions are found on both the upper and lower surfaces of the leaves and are not found on the husks. It can be distinguished from gray leaf spot by the presence of ruptures on the leaf surface which are visible with a hand lens.
Common rust postules on a corn leaf
Common rust postules on a corn leaf. Photo courtesy of Larry Osborne. Licensed under CC BY 3.0.
Common rust reduces the photosynthetic area of the leaves and also ruptures the leaf surface resulting in water loss. This leads to a weakened plant that may have poor kernel fill and is susceptible to stalk rot and lodging.
Fungicides can be used to treat common rust, although often the disease is not severe enough to justify treatment. They are most effective if applied at the first signs of disease.