Black spots appear in Kansas corn fields – what are they?

TOPEKA (KSNT) – Officials are monitoring the spread of a disease that is hurting corn production in Kansas.

The Kansas State Research and Extension Office posted a publication on June 30 regarding the spread of a disease that is causing black spots to appear on corn stalks in some parts of the state. The fungal disease, known as tar spot,

is established in some parts of the state and has been found in three northeastern counties in 2025 so far.

• Doniphan County – June 11.
• Brown County – June 17.
• Jefferson County – June 25.

Tar spot appears as small, dark, raised spots on infected corn and can appear on the leaves, sheaths and husks, according to K-State. The disease can cause crop losses if left unchecked.

“I think we have learned a lot in the last (few) years in terms of distribution and management,” said K-State Row Crop Pathologist Rodrigo Onofre. “It is one of the corn diseases that we see survive in corn residue, so folks that have seen this spot before are going to be dealing with this disease for a long time.”

Onofre said there are some hybrid varieties of corn that are especially vulnerable to tar spot and that early detection of it is crucial for crop management. He said it can be difficult sometimes to tell whether tar spot is in a corn field.

“For me, what really helps is you know if you get a wet cloth and try to clean that leaf,” Onofre said. “If it’s tar spot, it’s not going to rub off, but everything else will clean off.”

Onofre encourages corn producers to be vigilant for tar spot in their fields and take action by applying the right kind of fungicides. You can learn more about tar spot and other corn diseases by clicking here.

“The best thing that we could do for next year is start to think about more resistant hybrids, early scouting and a good herbicide management program,” Onofre said.

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