Corn growers found an unexpected visitor in their fields last season — southern corn rust.

Southern rust spread into over 100 new U.S. counties compared to the 2023 season, catching some corn
growers by surprise. In fact, it claimed the No. 2 spot behind tar spot in terms of U.S. corn bushels lost to disease in 2024, according to the Crop Protection Network.

Key points

• Southern corn rust continues to spread into new geographies each season.
• In severe cases, southern rust can cause up to 45% yield loss and impact profits.
• Growers can fight back against southern rust and other diseases with a preventative plan.
  

What is southern corn rust?

Caused by the pathogen Puccinia polysora, the primary symptom of southern rust covers corn leaves with orange pustules, inhibiting the plant from receiving sunlight and disrupting photosynthesis.

“Without necessary photosynthesis, you start seeing some tip back on the ears and you don’t see the 100% grain fill,” says Jorge Guzman, LG Seeds agronomist. “Kernels don’t mature enough, and your yields might be affected.”

Southern rust an annual concern in the South

Guzman, who serves growers in Texas and New Mexico, says his growers are used to southern rust. The disease thrives in warm, humid conditions and wet mornings that are commonplace early in the season.

Losses were limited in his territory this season, but that’s not always the case. Southern rust can cause up to 45% yield loss in severe cases, according to the Crop Protection Network.

Southern rust versus common rust

Distinguishing between southern and common rust can be challenging, but doing so is important. While the two diseases may look similar, common rust typically does not cause yield loss — a key difference between it and its southern counterpart.

Guzman advises corn growers to scout frequently, especially during pollination, and to pay attention to the pustules’ size, color and shape to help identify the disease.

“If you spot orange pustules that are more circular than oval on your corn leaves, you may want to spray for southern rust — but don’t wait too long,” he warns. “If a week goes by without action, it’s going to be harder to control.”

An unexpected visitor in the North

Seeing first-time pressure in several counties, LG Seeds Agronomist TeeJay Hagen had a different experience with his growers.

“To have southern rust this far north is a little unique,” Hagen says. “The disease doesn’t overwinter, so spores work their way up the Corn Belt as the winds blow.” According to Corn ipmPIPE, southern rust reports were confirmed in over half of South Dakota’s counties last season; these were the first confirmed cases in the state since 2020.

“Luckily, the disease appeared late summer, so while there wasn’t enough time for a fungicide application, it was late enough to not cause significant yield loss either,” Hagen adds.

Because this disease cannot overwinter, concerns about a repeat in 2025 are limited. However, Hagen says this disease is still something to keep an eye on.

“In the Upper Midwest, southern rust is something growers need to keep on the radar, but there’s probably more concerning issues this far north, like tar spot or northern corn leaf blight,” Hagen says. “Our biggest pest is corn rootworm, so there are other issues you probably want to take care of first.”

Multiple corn disease management solutions

Regardless of geography, both agronomists stress the importance of having a preventative plan in place to fight back against southern rust and other diseases. Fungicides are a common grower solution.

“If disease is a concern, it’s always good to come in with a preventative program,” says Guzman. “A preventative fungicide application has a lot of benefits, including control of southern rust.” Fungicides also reduce the risk of infection across the whole disease lineup, targeting more than one disease, Hagen adds.

Especially when coupled with fungicides, hybrid selection can also help protect against this disease. “We have hybrids with really good resistance to southern rust,” Guzman says. “If you have any concern with hybrids or have ideal conditions for rust, it’s always good to cross-check your plan with your agronomist.”

Reach out to your local LG Seeds agronomist to optimize your seed plans for any upcoming pest pressure.