Identify yield-limiting factors

JOHNSTON, Iowa — Every year is different in farming, but each year can also be a learning experience.

“We have to keep our eyes on using all of the tools that we can,” Michael Fosdick, Pioneer field agronomist in southeastern Iowa, said at the recent Corteva Summer Media Day.

“A good agronomy key is trying to identify yield-limiting factors, whether that’s nitrogen loss, mitigating risk, and talking to our growers about how we manage that nitrogen component.

“It’s not always about the nitrogen rate. It’s how do we split those applications up so we can mitigate risk, utilize a stabilizer like N-Serve or Instinct to help keep that nitrogen in the root zone, and how do we manage disease, whether that be with genetic tolerance in hybrid selection, as well as foliar protection with a fungicide?”

A large swatch of the “I” states experienced similar scenarios this growing season, ranging from dryness to significant rain events, then back to dryness.

“Every year has its challenges. June was a wet month and kind of dampened some spirits, but really the crop has transitioned out of that fairly well, and as long as we continue to finish this growing season with some timely rains, I’ve got some good prospects in the crop,” Fosdick said.

Heavy June rains did seem to hamper early soybean development.

“Those yellow pockets in poorly drained portions of the field did look pretty sad initially. They have rebounded out of it, and I’m cautiously optimistic,” the agronomist said.

“That variability is still going to exist out there, but certainly they recovered probably better than I anticipated in some regards with the weather we had to follow up with that.”

Fosdick was asked if the variable weather extremes, followed by high temperatures in July, impacts disease pressure, particularly tar spot.

“We’ve been seeing tar spot in eastern Iowa since 2021 in some way, shape or form, at some time throughout the season at different,” he said.

“When it does get hot in July, that’s not a real conducive environment for tar spot. It likes kind of more moderate temperatures. Leaf wetness is key. And we’ve had some of those hot temperatures kind of intermixed within our forecast to where it has kind of stalled out the tar spot.

“I do still anticipate probably seeing it to some degree, and then there are some isolated cases of it, but certainly it hasn’t been a perfect season for tar spot to progress so far.

“The key thing we tell our customers is when it comes to managing tar spot, it comes down to genetic selection. That’s the No. 1 thing to consider. We encourage farmers to look at what that genetic tolerance is to a disease like tar spot that can really be pretty significant if not managed.

“Secondly, with fungicide protection. We’ve got to use all of the tools in the toolbox to manage that disease.”

Keep Looking

Crop monitoring should for diseases should continue.

“Southern rust was a very significant disease for us in 2025. It’s been much slower this year, so I don’t anticipate that being near as significant for sure as last year, and thus far, with as late as southern rust is coming on, I don’t expect it to have that significance,” Fosdick said.

“On the soybean side, as we move into August, especially in those areas where we had a wet spring, that’s when sudden death syndrome tends to infect those plants. Usually if we have a perfect setup for that, we can start to see some of those symptomatologies as we move into August through that grain-fill period. So, we’ll keep an eye on that and identify those plants, and we certainly wanna make sure we can react accordingly.”

Nitrogen Availability

Among the concerns is the impact June’s heavy rains had on nitrogen in fields.

“I do have some concerns, depending on management practices, that the crop has enough nitrogen to finish strong,” Fosdick said.

“I think it’s a good year for growers to evaluate what their practices were this year to help mitigate risk for the future years. It’s not always about how much nice we put on, but how can we apply that in an efficient manner in multiple passes throughout that season to make sure we can mitigate that risk.

“When we think about heavy moisture in June, one of the big agronomic challenges this year on the eastern side of the state is nitrogen management. That’s probably going to be one of our potential yield-limiting factors in some cases this year, depending on drainage, soil class and that sort of thing.

“It’s been a tale of two growing seasons. In the eastern side this year, we dealt with a tremendous amount of rain in the month of June. We usually think about June being a drier month, which isn’t a bad thing as far as getting those roots down deep to weather the storm for the rest of the season.

“Fortunately, July has treated us a little bit better. We’re moving into that reproductive phase now where we’ve got to focus on disease pressure.”