DISEASES OF CORN - RUST

One of the most easily identified diseases of corn (or any other plant for that matter) is rust. The rust fungus produces reproductive structures (called pustules) that erupt through the surface of the leaf. These pustules produce substantial numbers of rusty-brown spores that give the disease its name. These spores are easily wiped off with your fingers.

The most common rust fungus of corn in Wisconsin is Puccinia sorghi, the cause of common corn rust. This fungus produces relatively large pustules on both the upper and lower leaf surface. Many times several pustules merge forming a long band. Puccinia polysora, a more southern rust species and cause of Southern rust, also occurs in Wisconsin occasionally. Pustules of this fungus are typically smaller than those of P. sorghi and occur most frequently on upper leaf surfaces. In addition, spores of P. polysora tend to be more yellow in color and more elongate that those produced by P. sorghi.

Rusts typically do not cause serious losses in field corn. Resistant varieties are available where needed, and for high value corn crops (e.g., seed corn or sweet corn) fungicide treatments can be used for disease control.