Southern Rust Spreads Across Missouri Cornfields

Southern rust is spreading across Missouri cornfields, causing concern among farmers. The disease produces clusters of small, orange-to-tan pustules on the upper surface of corn leaves and can be mistaken for common rust.

According to Mandy Bish, University of Missouri plant pathologist, southern rust is as aggressive as tar spot when it shows up in Missouri during persistently hot and humid weather conditions. The Crop Protection Network reported that the estimated yield loss last year from southern rust in the northern U.S. was 490.1 million bushels, with 26.2 million bushels lost in the South.

Farmers need to scout field edges first, where the fungus that causes southern rust cannot survive and spores have to move into the field. To differentiate between southern and common rust, look for pustules on the top of the leaf; if they break through the lower leaf surface, it's likely common rust.

The MU Plant Diagnostic Clinic can help determine whether a fungicide application is economically justified based on crop stage, disease severity, and weather conditions. Hot and humid weather will favor southern rust spread, making early scouting and accurate diagnosis essential to protecting yield.