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Tar Spot covers more Midwest fields this season

Tar spot, a fungal disease of corn, has spread to more Midwest fields this year. Jim Donnelly is an agronomist for Asgrow/DEKALB in Northern Illinois,

“With respect to my territory, I have a geography essentially from Interstate 80 North to Wisconsin. Every county has it, every field has it, every corn plant has it and probably every corn leaf has it.”

Donnelly says Tar Spot was found in the U.S. in 2015 and has been spotted in Northern Illinois fields the past three years, but the effects of the disease are worse this year since symptoms occurred earlier in the season and are more widespread. He says there is no treatment for the disease and now that crops have reached maturity, fungicides won’t help.

“Obviously for this year, you know, what’s done is done.”

Donnelly tells Brownfield that yield loss from Tar Spot has not been recorded in previous years, but some fields are expected to see significant yield loss this year. He says diagnosing the disease is simple, but there is still a lot to learn about controlling it.

“You can differentiate it from other diseases by taking the leaf and rubbing your finger over it. It will feel a little bit bumpy and other diseases may actually rub off whereas this one will not come off.”

Donnelly says because fields have the disease does not mean growers will suffer economic losses, but they should identify fields with Tar Spot and contact researchers to determine prevention plans for next year.

The University of Illinois is asking growers to send samples of Tar Spot to the Plant Disease Clinic to help with prevention research.

 

Audio: Interview with Jim Donnelly