Southern rust, a fungus that started affecting corn yields this summer, has been reported and confirmed, with higher concentrations in eastern and central Kansas.
“This southern rust probably typically originates in Louisiana and travels through Arkansas into Kansas in the southeast part of the state,” Doug Jardine, Kansas State Extension specialist for row crop pathology, said. “We have to verify the disease under the microscope to make sure it’s correctly diagnosed.”
A crop scout reported the first documented sign of southern rust in Labette County in late June. Jardine said southern rust normally appears in early August, but in the past several years it appeared earlier.
According to Crop Protection Network, southern rust of corn is caused by a fungus, Puccinia polysora. This corn disease is considered to be a tropical disease, spread by wind from southern climates into northern areas. Spores are also transported via clothing and other objects.
Once the fungus is established on the corn leaves, southern rust causes raised pustules and colored spores, resulting in ruptured leaf tissue. This damage negatively affects the plant’s ability to use water, according to the CPN. These pustules range from orange to tan in color and can spread rapidly from plant to plant.
The disease does die off with the arrival of colder months, as the fungus relies on a living host.
The CPN also reports Southern Rust thrives in high humid and high temperature conditions, given that it is a tropical disease.
“We can go from one extreme climate to another extreme year-to-year, so it will vary on how bad the southern rust will be,” Mary Knapp, assistant state climatologist for Kansas Mesonet, said. “This is a humidity-driven disease.”
Dan O’Brien, K-State Extension agricultural economist, said southern rust affects millions of corn bushels.
“You’re looking at about 13 to 14 million bushels of corn lost to southern rust in our local area,” O’Brien said. “Farmers have to look at marginal costs to treat the disease and make the decision to spend the money and if they will get that money back.”
Although 13 to 14 million bushels sounds like a lot, it is a very low percentage when spread over the large area affected by the disease. Farmers need to see what their loss would be before deciding on their management practices, Jardine said. He also said that while resistance is a big key in fighting off southern rust, fungicides should be a last resort.