New Corn Leaf Disease Spotted in Iowa

JEFFERSON CITY, Mo. (DTN) -- Curvularia leaf spot, a fungal disease of corn more typically associated with tropical climates, has found its way to central Iowa this season.

Alison Robertson, Iowa State University Extension field crops pathologist, confirmed the presence of the disease, which was observed in both a field trial and at a demonstration site in central Iowa on Aug. 14.

"We don't know a ton about this disease, but there are definitely differences in hybrid susceptibility to it," Robertson told DTN. "We still don't really understand what kind of impact on yield it will have, if any."

Caused by the fungus Curvularia lunata, the disease was officially reported in the U.S. for the first time in 2017 in Louisiana. Since then, it has been found in multiple states, including Delaware, Kentucky and Mississippi. The Iowa report of Curvularia leaf spot is the farthest north the disease has been observed and the first time its presence has been detected anywhere in the Corn Belt.

The disease may be more common when corn follows corn. Hot-and-humid conditions favor the disease. In addition, lesions tend to form on corn plants following rain that occurs during reproductive maturity.

"The frequent precipitation and very warm summer we have had definitely favored development of the disease," Robertson said. "Who knows if we will see the disease again unless we have summers with lots of precipitation."

The Crop Protection Network describes Curvularia leaf spot as small, tan-colored lesions with brown margins that may be surrounded by a yellowish halo. Lesions can be scattered across the leaf or in dense groups and can join into larger necrotic areas. Lesions are often observed on leaves in the mid to upper corn canopy, but they can appear at any growth stage.

Symptoms of Curvularia leaf spot can resemble those of eyespot. However, Robertson noted that disease is favored by cool, wet weather and generally observed early in the growing season prior to pollination.

While Curvularia leaf spot causes yield loss in tropical areas, its effect in the United States is not yet known. The disease is considered one of the most important diseases of corn in China. According to a 2022 article published in the journal ACS Omega, Curvularia leaf spot has become the third most serious leaf disease in China, following northern leaf blight and southern leaf blight. The percentage of yield loss in China ranges from 1.7% to 36.9%, with an average of 15.4%, based on two types of yield loss estimation models used by the researchers.

Crop rotation and tillage reduce the survival of the fungus. At present, foliar fungicides are not labeled for the management of Curvularia leaf spot.

"The next step for Iowa is to see how widespread it is this growing season," Robertson said. "Then, we will be monitoring it over the next few years just to see whether it will become an issue. The big question here in Iowa is, 'Will it survive our winters?'"

Curvularia leaf spot is one of the diseases for which the National Predictive Modeling Tool Initiative is developing models, Robertson shared. It will be one of the diseases eventually included in the Crop Disease Forecasting Tool available on the Crop Protection Network website.

That tool can be accessed here: https://cropprotectionnetwork.org/….

University of Kentucky Extension offers a publication on Curvularia leaf spot: https://plantpathology.ca.uky.edu/…

Jason Jenkins can be reached at jason.jenkins@dtn.com

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