A new disease that kills corn is spreading across the Midwest and Great Plains
By Harvest Public Media | By Eva Tesfaye
March 20, 2023, 9 a.m. ·
Tar spot is moving across the Midwest and Great Plains according to a report from researchers at Kansas State University.
The disease, which was present in Mexico, first appeared in Indiana and Illinois in 2015. Since then, it has spread to surrounding states — farmers spotted it in Nebraska for the first time in 2021 and in Missouri, Kansas and South Dakota last growing season.
“It's spreading, I'd say, pretty quickly, throughout the Midwest in the corn production regions,” said Rodrigo Onofre, a plant pathology professor at Kansas State University.
The fungal disease attacks leaf tissue in corn and can rapidly deteriorate the plant. According to the Crop Protection Network, it is estimated that it caused farmers to lose around $3 billion in the United States from 2018 to 2021 and has the potential to be more destructive in states that are just now seeing cases.
“It's a significant disease. It can cause a significant loss to our growers, so I think that's the main concern right now,” Onofre said.
The fungal pathogen that causes the disease survives over winter, meaning that the disease won’t go away.
“Once you have it, you're not going to get rid of it. It's going to stay on that corn residue in that field,” said Mandy Bish, integrated pest management coordinator at the University of Missouri.
Since it’s still early, farmers will have to wait to see how much of an effect tar spot will have in states where it’s just appearing. It thrives in mild temperatures and wet leaves.
“We're learning some of those environmental conditions,” Bish said, “so we know that in 2018 and 2021 we had really bad outbreaks in those states that caused significant yield loss, whereas in 2020 and 2022 the environmental conditions weren't as favorable.
Both Onofre and Bish said there are ways to manage tar spot. Farmers can prepare this year by choosing corn hybrids that are more resistant. The disease can also be managed using fungicides.
“What I try to tell our farmers in Missouri is we don't want to make fungicide applications out of fear,” said Bish. “We want to scout, but we also don't want to be complacent.”
Farmers are encouraged to report any sightings to their local extension office and to save the leaves so that the extension can confirm the disease. There is also a website called Corn ipmPIPE where farmers can report tar spot and get identification from extension specialists.
Eva Tesfaye covers agriculture, food systems and rural issues for KCUR and Harvest Public Media and is a Report For America corps member.
This story was produced in partnership with Harvest Public Media, a collaboration of public media newsrooms in the Midwest. It reports on food systems, agriculture and rural issues.
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