Nathan Kleczewski has been fielding phone calls and Twitter mentions, sometimes more than a dozen a day, from farmers asking him if the black flecks and lesions on their corn plants are symptoms of a new disease: tar spot.

Kleczewski, professor in ACES, has been trying to unravel the causes of tar spot, which is a fungal disease that can reduce corn harvests by more than 30 percent.

As of last Friday, Kleczewski has used the responses from farmers and growers to identify 18 Illinois counties in 2018 that have been hit by tar spot, including Champaign County.

“There’s a lot of concern out there because we don’t know a lot in terms of what the pathogens are doing, how to control it and what people’s options are,” he said.

The black spots and accompanying brown lesions likely result from a combination of two fungi and can spread rapidly through the leaves and husks, killing the plant quickly, Kleczewski said.

“It’s in virtually every cornfield in northern Illinois,” said Jim Donnelly, technical agronomist for DeKalb Brand Corn and Asgrow Seed Company. “It’s worse mostly because of its ability to spread pretty rapidly as well as the fact that the vast majority of hybrids out there are fairly susceptible. That combination has allowed that disease to move and increase very quickly.”

Donnelly said he typically sees a 10 percent reduction in yield, but expects to see a few cases where farmers lose almost half their harvest to the disease.

Kleczewski said tar spot, common in damp tropical climates, was first identified in Illinois in 2015, when heavy rainfall likely caused its explosion across the U.S.

Kleczewski said tar spot is the most severe corn disease in Latin America, and with persistent rainfall this year, the disease has erupted across Illinois and the midwest.

Kleczewski hopes to be able to develop a corn plant resistant to tar spot. If tar spot proves uncontrollable, he said the team may develop online maps to help farmers identify whether their crops are at risk of contracting the disease.

Far from identifying a cure for tar spot, Kleczewski said the researchers are still trying to identify what’s causing the lesions.

Farmers have applied fungicide to their crops in the hopes of preventing tar spot with mixed results. Despite applying the same product at the same time, some fields became infected with tar spot, while others did not. Kleczewski said he thinks the reason is because the spores arrive in the fields at different times, but doesn’t understand what causes the spores to be released, or how far they travel.

“Especially after this year, people in the northern part of the state are concerned about it. The industry is asking questions every day. There are a lot more questions than answers,” Kleczewski said.

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