Tar Spot Reduced Corn Yield Significantly in 2018; What Will 2019 Bring?

Tar Spot Reduced Corn Yield Significantly in 2018; What Will 2019 Bring?

Purdue Extension Field Crop Pathologist Darcy Telenko

Chances are, if you’re a farmer, you’ve heard about tar spot in corn by now. Hopefully, though, you haven’t had to deal with it yet like some Northern Indiana farmers. Purdue Extension Field Crop Pathologist Darcy Telenko says this is still a new disease, popping up in the US for the first time in 2015, with little research done. But after last year, Telenko wants more data after finding that it can lead to severe yield loss.

“What we’re trying to do is just gather that information to really understand a bit about this pathogen and how do we manage it. At the end of the (2018) season, we estimate that we saw 20-50 bushel yield losses in some of those hard hit fields.”

11 counties up near the Indiana/Michigan state line have fields with a positive test result for tar spot. Telenko says it’s easy to spot tar spot as it looks like someone splattered the leaf with tar from a paint brush.

“The unique thing about this is if you touch that leaf, it’s almost like a raised bump, and if you scratch at it that spot is not going anywhere. If it’s an insect or some other issue, it generally will rub off. Some of the other diseases may be sporulating, you might get some of those spores on your fingers, but again the tar spot, it’s a raised bump, looks like a black spot, but it could be anywhere from a spot to an elongated lesion and there may be hundreds a little spots there.”

Telenko said that last year was the “perfect storm” for tar spot and it exploded early in the canopy causing those significant yield losses. What about this year?

“As of 2-3 weeks ago, we are starting to see more activity. We have research plots up at Pinney (Purdue’s research farm on the Porter-LaPorte county line) and it’s moved in the lower canopy and it’s slowly making its way up, but I’ve been in fields this past week that have 100 percent infection and the corn is infected all the way to the top. That being said, most of our corn is reaching R5 maturity, so I don’t know the yield impacts will be as bad as we saw last year, but we do have some severely infected fields.”

You can learn how to submit a crop disease sample here.

Listen to the full interview with Telenko below for more info on tar spot and other diseases impacting corn and soybeans across the state.

Purdue Extension Field Crop Pathologist Darcy Telenko

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