How Powerful Corn Weed Control Pays at Harvest

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Fall is the time when corn farmers are able to see the fruits of their labor from the rest of the year and get an idea of how successful their management programs were. As you watch the yield monitor count up during harvest this season, you’ll likely be evaluating what went right – or possibly wrong – so you can see where to make changes in future seasons.

One area that has a major impact on how high the monitor goes is weed control. If your weed control program wasn’t as successful this year, your corn yield will likely suffer. That’s why it’s so important to reflect on how weeds can rob yield — and how keeping fields clean throughout the season can really pay at harvest.

Weeds Rob Corn Yield

Nick Burke is the U.S. product manager for corn herbicides at Corteva Agriscience. He says weeds act as competition to corn and other crops when it comes to resources like sunlight, water and nutrients.

“As an example, weeds can be particularly competitive if they’re already emerged when corn plants are still seedlings. They can crowd out young corn, blocking out necessary sunlight, in addition to simply competing for nutrients and water,” Burke says. “And in cases where water may be limited due to drought or nitrogen is limited because of loss, corn plants will be under additional pressure, making the opportunity for growth — and yield production — even more difficult.”

Burke says yield loss due to weeds is heavily dependent on a number of factors, “including the varieties of weeds present, the growth stage of those weeds and the timing of herbicide applications, to name a few.”

But, as an example, let’s look at the numbers based on waterhemp. According to the Iowa State University Extension, waterhemp can reduce corn yield by anywhere from 5% to 20% depending on weed density. If you’re growing 200-bushel-per-acre corn and you have a waterhemp problem, that could mean 10 to 40 fewer bushels per acre. If corn is $6.75 per bushel, that’s between $67.50 and $270 lost per acre. If you grow 500 acres of corn, you could be looking at up to $135,000 lost.  

Control Weeds Early

Burke says clean fields are essential to maximizing corn yield potential. However, weed control timing is incredibly important.

“It may be possible to get clean cornfields a number of ways. Maybe you can get weeds cleaned up with a postemergence application only, or maybe you need a full program that includes multiple passes with several modes of action and residual activity for clean rows,” Burke says. “However, there does seem to be a vast difference in yield potential between cornfields that are clean throughout the growing season versus fields that are cleaned up later in the year.”

According to this article on, weeds can start reducing corn yield if they’re present as early as the V2 growing stage — and the risk to yield potential grows exponentially from there.  

“The height of the weeds present also has an impact on corn yield potential,” Burke says. “The taller the weeds when they’re controlled, the more likely they are to have a negative impact on yield.”

Going back to the Pioneer article, you’ll see 2-inch weeds, for example, can cause up to 7% corn yield loss, whereas 12-inch weeds can cause up to 22% yield loss.

“Knowing this, it’s in corn farmers’ best interest to control weeds early and often with a full program approach,” Burke says. “I recommend starting your weed control program with a burndown application, making a preemergence application that includes multiple modes of action and residual activity, and following that with a timely postemergence application that also includes multiple modes of action and residual activity.”

Burke says using a program that includes powerful solutions will help control weeds when they’re small — and the residual activity will help keep new weeds from emerging. He says this ultimately helps maximize corn yield potential.

To find the right solutions to control weeds and maximize your corn yield potential, visit the corn herbicides portfolio page on   


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