Harvest reveals past, potential weed issues

SOUTH BEAVER DAM, Wis. — With harvest rolling along, revealing the good, the bad and the ugly, it’s an ideal time to evaluate weed pressure and plan for 2027.

“The combine is not the best scouting tool,” said Nick Groth, Syngenta agronomic service representative.

“What I’ve seen at the end of the season, maybe you have some weed escapes in cornfields, you tried to clean it up, but a lot of those plants are still there. They maybe got twisted up or beat up by the combine, but they came back, and now they’re putting on a little bit of seed. It’s something that we’re going to have to deal with next year and for years to come.

“It can be a hidden issue in corn where the crop is tall enough that whatever waterhemp escapes that are out there, they don’t get above the crop. You don’t see them.

“You don’t realize they’re there until combine time. Sometimes you don’t know at all because you’ve had a frost or something that happens before the combine goes through and you don’t realize all the weed escapes you had and the seed production that follows.”

Waterhemp

Waterhemp continues to be the No. 1 weed farmers are struggling to control due to herbicide resistance.

In late 2025, several populations of glufosinate-resistant waterhemp were confirmed in northern Illinois by the University of Illinois. Waterhemp populations have now been found to be resistant to seven post-emergence herbicide groups of products.

“Strong residuals is the place to start with waterhemp management. I think we’re all moving more to higher rates of more robust products, but we did have a few challenges in areas with activating rainfall, which is always another challenge,” Groth said.

“If you get these strong residuals out and you don’t quite get it activated perfectly, you can have some escapes from that. It certainly was not as bad as last year, but that was part of the challenge.

“What I see now as the biggest challenge in waterhemp management is whatever escapes we have, whether that was too light of a pre-emergence or poorly timed post-emergence applications, it just seems like escapes that we have when we make a rescue application or a plant post-emergence application are really difficult to knock down.

“Relying on a few ounces of Callisto like we used to in the past or a dicamba-based product just hasn’t been enough to really knock down waterhemp populations once they get some size to them, especially if there’s any density out there, if there’s a number of them or if they’ve got size. Our post-emergence options are so limited for controlling these.”

Looking Ahead

The combine pass reveals if the weed management strategy was adequate that year.

“That’s the time where we’re going across all the acres. We get to see it all. It’s an opportunity to look at which fields had successful programs where the weed control is good and which fields had some challenges,” Groth said.

“What should I do in the future to just know that, OK, this field has escapes and there’s going to be more seed production here. What I did this year wasn’t exactly performing the way I had hoped. It’s going to only be harder next year. What can I change in my program to make sure that we’re able to have a successful weed control program next year?

“In a lot of cases, it means moving to a robust program, introducing more effective sites of action, and/or increasing rates to try to build a more robust program that really deliver weed control in these variable environments that we face.”

Start Clean, Stay Clean

Groth stressed the need to start clean and stay clean in terms of weed control for a couple of reasons.

“A weed is much easier to control when it’s in a seedling stage than it is once it has size. We just have much more higher success rates out of residual chemistry than we do out of post-emergence chemistry,” he said.

“But there’s an added value in the yield preservation component, as well, because that corn crop, or any crop, sees the weed competition around it, and it wants to grow above that weed competition. So, it sacrifices root growth, it tries to get taller and stay above those weeds, and you really inhibit that plant’s ability to recover from that early-season stress.

“So, now it has a poorer-developed system. The weeds have already taken water and nutrients from the soil. Poorer roots get less water and nutrients from the soil, and that impacts yield.”

Tight Budgets

In times such as this, with high input costs and volatile commodity prices, Groth was asked what farmers should consider when looking at ways to reduce costs.

“A key piece of the equation when margins are tight and growers need to examine every piece of their budget is what are critical components of their operation and where they can maybe pull back a little bit and try to save a little bit of money,” he said.

“I think crop protection is a place where guys tend to look, both fungicide and herbicide. Specifically on the herbicide space, there are good options that may be cheaper, but they’re probably not the premium option. They don’t come with the very best chance of success and they lack in other areas, not just in the active ingredients and the active ingredient loads.

“You take a product like Storen where we have multiple effective sites of action. We spent a lot of time getting the rates right, getting the crop safety component rights and matching this flexibility of use, ease of use, crop safety and performance.

“Going away from these kind of premium pre-mix products, trying to mix your own and trying to find just the right key components, maybe in the generic space, for example, it’s possible to make a successful program, but it definitely gets to be a challenge. You just don’t have the formulation stability.

“You don’t have all the science and the research behind it to back up that this is a product that has the correct modes of each effective active ingredient. Also, that it’s formulated in a way that you’re going to deliver that effective load, and it’s been tested, and you can assure that it’s going to be safe to the crop.

“It’s just something that you give up when you go away from a premium pre-mix. It’s just the full robustness of these premixes and all the value they offer.”