Tar spot disease continues to damage Indiana's corn crop

78 counties are now dealing with active tar spot. The disease is expected to result in significant yield loss for growers this year.

Posted: Oct 11, 2021 10:35 AM
Updated: Oct 11, 2021 10:46 AM

TIPPECANOE COUNTY (WLFI) — Tar spot disease is continuing to cause extensive damage to Indiana's corn crop.

In News 18's previous Indiana Farm Report in July, 11 counties in Indiana reported positive cases. But now, 78 counties are dealing with active tar spot. 

“Tar spot is a new disease here in Indiana,” said Purdue Field Crop Extension Pathologist, Darcy Telenko. “We first found the disease in 2015 and the problem is it’s causing significant issues in corn here in Indiana.”

Telenko said growers saw big issues in 2018, but now we’re seeing bigger issues in 2021.

"We did see a couple of new counties that we found it in this season,” said Telenko. “So if you look at our map you can see that most of that state has turned yellow where we have an active tar spot.”

Telenko says the conditions were favorable for the disease to rapidly spread this year. 

"For tar spot, it's moisture," said Telenko. "It requires a long period of leaf wetness to get started and those continual wet conditions will cause the disease to really ramp-up within the crop canopy."

Telenko says growers in Northern Indiana have seen the most damage. 

“We had a lot of issues up in northern Indiana and then there’s some pockets around the state where they right the right moisture conditions that the disease took off,” said Telenko. “Where the center part of the state kind of was droughty tar spot really isn’t causing problems but it’s there, it’s probably in most fields if we looked hard enough we would be able to find it.”

Telenko says once tar spot is found, it’ll continue to spread and affect the crop. The disease causes the crop to shut down early. Because of this, Telenkso says the crops are not getting to black layer before they shut down.

“We’re still trying to understand the epidemiology of this pathogen,” said Telenko. “We know it takes little time for the first infection to occur, but then those multiple cycles it just seems to ramp-up once it gets in the corn, especially if we have those wet conditions.”

As News 18 previously reported, the USDA is forecasting record breaking yields for corn this year. However, Telenko believes tar spot may change the outcome. 

"So tar spot will significantly have a big impact in what happens in particularly northern Indiana in those pockets," said Telenko. "The problem is it's an obligate pathogen. It really likes living green tissue so our best fields are the ones that this disease likes to infect and cause problems." 

Tar spot disease was first identified in the United States, esspecially Indiana and Illinois, in 2015 where it mainly impacted the Midwest.

At this time 12 states have confirmed cases, including Georgia.

“Right now from what we’ve seen and what I’ve seen rotation and tillage really isn’t going to help reduce the disease in future seasons,” said Telenko. “It may help the initial start but what we’re seeing is it could’ve been soybeans last year and the field may have had tar spot two years ago and it’s still really bad this year.”

Tar spot is something Northern Indiana Farmer, Eric Wappel, has been dealing with for a few years.

"In 2018 we found a few spots here and there but in 2019 it was the first year we started doing things about it and trying to figure it out," said Wappel. "Then last year it wasn't a perfect weather event year we had it widespread last year and it didn't affect us near like this year. This year it was like a freight train. It just plowed on through."

Telenko says tar spot is a fairly new disease, but from what she's seen so far rotation and tillage really aren't helping reduce the disease for future seasons.

"It may help reduce the initial start," said Telenko. "But what we're seeing is it could've been soybeans last year and it may have had tar spot two years ago and it's still really bad this year."

Once you identify tar spot, Telenko says it's important to keep field records of what the disease looks like. 

"I would say that if it was my farm I would be going out and looking at how the different hybrids on your farm reacted to the disease."

Keeping an eye on how the hybrids is exactly what Wappel has done.

"We're seeing a huge difference in hybrids this year," said Wappel. "As far as how long they stayed alive and how they fought the tar spot off."

One thing Telenko says they've learned from this year's outbreak is timing for fungicide applications was critical.

"This year probably we should've gone out with fungicides earlier in the late vegetative stages and then possibly add a second fungicide application to maintain disease control," said Telenko. 

Moving forward, Teleko says this winter she will be collecting the data and trying to determine what fungicides worked best.

 "Moving forward you just need to understand if the disease on your farm and did it really cause problems this year," said Telenko. "If you have a few lesions it probably didn't cause significant yield losses but the disease is now there."

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