3 Weeds Causing In-season Headaches in Corn This Summer

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Sometimes, despite our best efforts, weeds can escape herbicide applications and other control measures, causing headaches throughout the growing season. And depending on the species, when they appear and how big the populations get, these weeds can have a negative impact on yield and make harvest more difficult.

Luckily, there are steps you can take to mitigate the issue now and in the future to help ensure good yield potential. Two Corteva Agriscience market development specialists have insights into the weeds they’re seeing in-season and advice to control them.

Weeds We’re Seeing in Corn

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Jeff Moon and Nate Wyss are market development specialists working in the Midwest. Moon works in Wisconsin and Minnesota, and Wyss covers Indiana. They say there are three weeds in particular that are making trouble in their territories this time of year.


“Giant ragweed and waterhemp are a continual concern in the geography I cover,” Moon says.

Wyss is seeing the same, with one addition: “The three toughest weeds we face across Indiana are waterhemp, giant ragweed and marestail. These weeds have been the predominant species that we’ve struggled with in Indiana for five-plus years.”

“The three toughest weeds we face across Indiana are waterhemp, giant ragweed and marestail.”



Giant ragweedmarestail and waterhemp can be yield-limiting, and they’re all difficult to control for a number of reasons. Chief among those reasons is herbicide resistance.

“All three are commonly glyphosate-resistant. Waterhemp has potential to be resistant to seven different herbicide groups,” Wyss says.

Moon adds, “They certainly can be and likely are resistant to multiple modes of action.  I think we need to assume they are when we prepare a weed control program.”

This resistance can lead to populations of the weeds escaping pre- and postemergence herbicide applications and remaining in cornfields or showing up later in the season.

“They certainly can be and likely are resistant to multiple modes of action. I think weneed to assume they are when we prepare a weed control program.”


Controlling Corn Weeds Now

The first step toward controlling these weeds is finding any escapes. Then, if you find them, you can make a plan to keep the situation from getting out of hand.

“The best thing to do after a postemergence application is to intensively scout fields to see if any weeds were missed by the application and decide on next steps if there are any weeds present. This can involve another herbicide application, hand-spraying weeds in the field, or physical weed removal to lower populations of weed seed,” Wyss advises.

Large weed populations can make corn harvest difficult by getting tangled up in machinery. Harvest can also spread these weeds’ seeds, adding to the seedbank and making weed control harder in the future.

To avoid these issues, Wyss and Moon advise talking with your retailer to see if it makes sense to make another application preharvest. There are some solutions with relatively short plant-back requirements that can be applied to at least desiccate weeds, drying them down and making harvest easier.

“If there are trouble spots, a preharvest or postharvest strategy may be needed. This is also a good planning exercise for the following year. Knowing your weed problems and knowing where the trouble spots are will keep you on the right track,” Moon says.

“Knowing your weed problems and knowing where the trouble spots are will keep you on the right track.”


Controlling Weeds Next Year

Moon and Wyss advise noting what weed escapes you’re seeing now and where they are and then using that information to create a good plan for 2022. They say resistant weeds like giant ragweed, marestail and waterhemp call for a full weed control program approach.

“They require a long-term, sustainable approach to see the best results. A two-pass program with multiple modes of action will give us the best shot at exceptional weed control and protect yield. We have some really good options in our portfolio of products at Corteva Agriscience,” Moon explains.

A few of those options include a preemergence application of SureStart® II herbicide, followed by a timely postemergence application of Resicore® herbicideResicore® XL herbicide will also be a good choice to control these weeds when it becomes available. The new product is currently on track for registration from the U.S. Environmental Protection Agency in 2022.

And Wyss says it’s important to remember to give your weed control program a strong start. “Ensuring an effective burndown application or utilizing tillage to start the season is key,” Wyss says.

A strong weed control program approach can lay the groundwork for a successful season and good yield potential. Part of that program should include regular scouting for weed escapes and making any necessary changes to control those weeds, both in the present and the future.

Resicore® XL has not yet received regulatory approvals; approvals are pending. The information presented here is not an offer for sale. Resicore and SureStart® II are not registered for sale or use in all states. Resicore and SureStart II are not available for sale, distribution or use in Nassau and Suffolk counties in the state of New York. Contact your state pesticide regulatory agency to determine if a product is registered for sale or use in your state. Always read and follow label directions. 

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