First 2018 Case of Southern Rust in the U.S. Confirmed by MU Extension

The warm and humid weather conditions in Missouri have likely expedited the emergence of southern rust in 2018.
The warm and humid weather conditions in Missouri have likely expedited the emergence of southern rust in 2018.

The University of Missouri Extension has officially confirmed the 2018 growing season’s first case of southern rust corn disease in the U.S. The confirmation came on July 10 from a sample collected from west-central Missouri, according to the MU Plant Diagnostic Clinic.

Typically, the disease shows up in neighboring southern states before appearing in Missouri, but this year is an exception.

Southern rust is a “tropical” disease that overwinters in warmer climates. The disease favors temperatures around 80 degrees Fahrenheit with relatively high humidity. As the fungus multiplies in the host tissue, pustules form. Masses of spores then erupt through the leaf tissue.

MU Extension plant pathologist Kaitlyn Bissonnette says there are a few things to consider when looking out for the disease. Orange-to-tan circular or oval pustules commonly form in dense clusters on the upper leaf surface when a crop has the disease. The pustules may eventually turn to brown or black.

Rust also often initially shows up in the mid-to-upper plant canopy. It typically appears along field borders or at the ends of rows where spores can easily land on leaf surfaces. Bissonnette notes that southern rust is commonly confused with other types of leaf diseases, and proper diagnosis is essential to avoiding costly fungicide applications.

“Take note of the current distribution of southern rust in the area, the growth stage of the crop and the environmental conditions,” says Bissonnette. “These are the most important factors to consider when making decisions to apply fungicides.”

More information on southern rust and its management can be found by visiting CropProtectionNetwork.org.