A fungus that attacks corn has spread to over 40 Iowa counties.
Southern rust creates reddish-orange patches on the tops of corn leaves. This blocks photosynthesis, which weakens the plant and can reduce yields. Severe cases in Florida reported losses up to 45%.
“It's unlikely that we would see yield losses that significant here in Iowa, but there is potential this year to see more yield loss than we would see in a usual year,” said Meaghan Anderson, an extension field agronomist with Iowa State University.
She added that this isn’t the first time southern rust has been found in Iowa. But it was detected earlier this year with reports coming in mid-July. The disease is also much more widespread.
“We’ve had so many storm systems and so much wind this summer, that we've had more movement of those spores from the Southern United States up into Iowa,” Anderson said. “But then we've also had continued activity and hot and humid conditions that it likes that appear to have allowed it to spread further.”
Dan Bjorklund, a Landus technical agronomy advisor, said his team found southern rust across the state with the help of drones that take thermal images. They flagged crops that were in distress to inspect in person.
“In 46 years that I've been agronomist, [southern rust has] only been up in Iowa a couple times,” Bjorklund said. “It's really damaging. We're not used to it up here.”
Farmers can use certain fungicides to manage southern rust, but it only protects the crop for about two weeks in high disease, he said.
Recommendations
“The best thing for any farmer is go out and look in your field,” Bjorklund said. “If it was my field, I would be out there looking, I mean, every three days.”
Anderson emphasized scouting beyond field edges to understand how much southern rust may have spread within a field.
“Most corn is getting far enough along in development that fungicide applications should be slowing down, but if this disease is prevalent and conditions continue to favor its spread, corn may benefit from applications later than we typically recommend,” she said.
Since fungicides vary in their effectiveness against southern rust, Anderson recommended farmers check the Crop Protection Network website for information.
Other corn leaf diseases
Anderson hopes that cooler temperatures will slow the spread of southern rust.
But with the heavy amounts of rainfall and humidity this summer, there’s greater potential for a “potpourri” of corn leaf diseases. She added that some corn hybrids are more susceptible to diseases than others.
“One that we've seen a lot this year, more so than in a typical year, is a disease called bacterial leaf streak,” Anderson said. “That's a disease that we can't actually manage with fungicides, like we could try to manage southern rust and some of our other pathogens.”
Bacteria enter the plant through tattered leaves or potentially the open pores on the undersides of the leaves. Heavy winds and rain help spread bacterial leaf streak, she said.
Tar spot, gray leaf spot and northern corn leaf blight are also showing up in some fields. Bjorklund said Iowa corn farmers could have a record yield this year if they can keep disease pressure at bay.
“I don't know a time when I've seen better pollination and better ear size for this time of the year,” he said.
