Tar spot

Statewide disease levels low (so far)

The 2022 Ohio Crop Tour is made possible by Ohio Field Leader — a project of the Ohio Soybean Council and soybean checkoff.

By Matt Reese and Dave Russell

While there was plenty of concern heading into 2022, tar spot has not been showing up on any large scale in Ohio’s corn fields.

“Tar spot is the big concern but I have not been able to verify that in any field I have been in yet this year. Last year is the first year we had it in Allen County and it didn’t come in until mid- or later-August,” said Clint Schroeder, Ohio State University Extension Educator, Agriculture and Natural Resources in Allen County. “Then we had the fall armyworm. That all came in county fair week last year. We do not have a ton of experience with tar spot. It is a relatively new foliar disease for us. We have to understand how to identify it and manage it if you do have it. We have a lot of Extension resources on making decisions, timing and the products to use. We could make the case that it can certainly take off top end yield and we have to be vigilant about keeping an eye on that.”

Tar spot is a foliar disease that really has not been on the radar for Ohio up until just the last few years. In 2021, it became a more widespread issue in Ohio. According to plant pathologists Pierce Paul and Jorge Valle with Ohio State University Extension, tar spot is relatively easy to diagnose based on visual symptoms, though other diseases can look fairly similar. Tar spot is characterized by raised, black tar-like spots, but southern rust, common rust and insect frass can have a similar appearance. 

“Tar spot stromata do not rupture the leaf or have a split on the top. In addition, they cannot be easily broken or rubbed away with your fingers like rust or insect frass. Rust telia usually break or rupture the upper surface of the leaf tissue, and if rubbed, the spores are released, leaving your finger with a dark-rusty to blackish tinge,” Paul and Valle wrote in a 2022 CORN Newsletter.

Beyond tar spot, Ohio’s crops seem to be facing consistently low disease pressure statewide, in spite of the warm, wet conditions.

“The corn is very clean. I’ve been looking GLS, tar spot and NCLB. I have been very impressed with how clean the corn is, but we’re going to continue to keep an eye on those diseases,” said Nick Eckel, Ohio State University Extension Educator, Agriculture and Natural Resources in Wood County. “With soybeans it is pretty much the same story. We really haven’t seen much frogeye. For the most part we have been pretty good on the insect and disease front.”

Further to the south and west in Darke County the story is much the same. 

“Most of the fields I would rate as good to excellent. So far I think we have some fairly promising yields for the amount of stress they’re had this summer. In most of the corn fields I have been in, I haven’t seen a lot of disease or insect pressure. Normally you have a little NCLB and GLS pressure by now. I have seen it here or there and really only in the lower part of the canopy. I think the dry weather we had earlier really helped back off the later season disease pressure we would normally have. We had a couple of fields in Darke County last year, but I have not seen tar spot in Darke County this year. I had a couple of scares in the county but nothing confirmed as tar spot so far,” said Taylor Dill, Ohio State University Extension Educator, Agriculture and Natural Resources in Darke County. “The soybeans had a really rough start but most of them are starting to look really good. I am pretty optimistic on soybeans. They also have fairly low disease pressure. I haven’t seen any frogeye out there. There is a little insect pressure in soybeans, but we have some really resilient crops and that shows this year.”

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