Iowa tar spot map

A map shows the counties where corn tar spot has been found. Red marks a county with a positive report of tar spot, while yellow indicates a probable identification. 

Despite the rain and delays in planting, farmers may have dodged a bullet in some areas this year.

While the crops still have a way to go, some crop advisors in Iowa are saying disease has not been as prevalent in their coverage areas.

“I can’t think of anything we are finding in our area,” said Charles Smith, agronomy manager at Smith Fertilizer and Grain in south central Iowa. “We have guys north of us spraying for bugs, but I’m not sure how much they are spraying for to be honest.”

In northwest Iowa, Hal Tucker of Tucker Consulting said they are dealing with a few issues, primarily physoderma brown spot and stalk rot in corn.

“That seems like it’s having an impact on the ear side,” Tucker said. “It’s very common in the field.”

Frogeye leaf spot has been found on some of the northwest Iowa soybean crop, but Tucker said it “hasn’t been an epidemic.”

He said the past prevalence of the disease has led to changes in his area, where people are planting different varieties to get ahead of the problem.

“I think people are thinking about it when they look at their variety lineup,” Tucker said. “The seed companies are thinking ‘there’s a frogeye issue in the area, and we have a fungicide that doesn’t work very well. We aren’t getting much success with control over it.’”

Iowa State Extension reported multiple instances of corn tar spot, with 15 Iowa counties reporting at least one positive identification, most near the Mississippi River in northeast Iowa.

Frank Moore, from Three Rivers Consulting in Cresco, Iowa, said he has not heard about tar spot being too much of a yield issue. He said stand issues are popping up in northeast Iowa, but otherwise he hasn’t seen too many problems with the crop this year.

His main concern is the maturity of the crop to start September.

“We have to try and get this in before freeze comes,” Moore said. “It’s probably a month out. We are starting cover crop seeding tomorrow, and normally you want to do that when the crop is starting to turn color and you can get some light penetration in the canopy. Everything is still green here.”

Moore said he planted corn on June 2, the latest he has ever planted aside from replant situations, and said he is still seeing some white kernels.

“If we get an early freeze, there’s a potential there’d be zero yield on that particular farm,” he said.

His early yield checks have been “disappointing,” Moore said. He is expecting between 170-180 bushels per acre. Moore added that he does not foresee any combines moving until after the calendar flips to October.

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