Fighting waterhemp, a weed 'born for the 21st century'

Pigweed, a general category that includes the increasingly worrisome waterhemp and Palmer amaranth, requires bold ideas and determination to control, a weed scientist said.

waterhemp seed head ndsu.png
A waterhemp seed head. (NDSU Extension)

Upper Midwest farmers are accustomed to battling weeds. But the battle will be especially difficult with waterhemp and require bold ideas, a weed scientist said..

"Producers need to consider extraordinary action as they prepare for 2021 to beat pigweed including waterhemp. So far, we have learned waterhemp is different from other weeds; a formidable foe requiring producers follow a different script for control," one that requires "bold ideas," said Thomas Peters, extension sugarbeet agronomist and weed control specialist for North Dakota State University and the University of Minnesota.

Peters spoke Dec. 10 at the annual Prairie Grains Conference in Grand Forks, N.D. The event, hosted by a number of North Dakota and Minnesota commodity and general farm groups, was held online this year, with all the sessions on one day instead of the normal two.

Peters noted that many of the people attending the event raise wheat and soybeans. He emphasized the need for an integrated weed control system that covers all the crops they raise and that controlling pigweed in wheat and soybeans is "crucial."

Pigweed, a multistemmed summer annual in the Amaranth family, is a rising concern in the Upper Midwest. Waterhemp and Palmer amaranth are among several pigweed species. Palmer amaranth has drawn considerable attention in the past few years, and Peters said waterhemp warrants the same level of concern.


"If we don't get aggressive (in dealing with waterhemp) in the next two to three years, I believe the next generation of farmers are going to change their practices because of waterhemp. That's how important waterhemp is to us," he said.

"We can't rely on herbicides alone. If we do, waterhemp will be our No. 1 production problem. Not our No. 1 weed problem, our No. 1 production problem," Peters said.

Peters compared fighting pigweed to college football teams being fully prepared to play games.

"Pigweed will be prepared to play once spring comes. It's critical that we use our winter meeting season to learn as much as we can about waterhemp (and) to consider various options and to be prepared to take decisive action. because that's what it takes to manage waterhemp," he said.

Why is waterhemp so difficult to manage? "It's a weed that was born for the 21st century. It fits perfectly into modern-day agriculture," Peters said.


  • Initially, there were only a few plants, in scattered fields, that led to early misidentification.
  • It germinates and emerges all summer, "which is pretty unique."
  • It grows very rapidly, especially in an environment where climate is changing and that features weather hotter and wetter than normal.
  • It's well adapted to conservation tillage.
  • Farmers use a lot of post-emergence herbicides, which plays into waterhemp's ability to germinate and emerge all summer.


Peters gave five recommendations on how to fight waterhemp.

The first is developing a weed control program for each crop that's based on cropping history, weed pressure and what will be planted on the field. "Farming by the averages, where we do the same thing over and over, doesn't work for waterhemp. You need personalize control for each field."


Planning crop sequences is the second. "Map out each crop you plan to crop and what your herbicide options are."

Third, "If you have to, bury the (waterhemp) seed" by plowing it deep into the soil.

Four, "Tailor your programs," which means picking out nozzles and water volume on your sprayer for specific weeds.

Finally, "Attack, attack. Don't rely on herbicides alone. Use an integrated approach."

Peters also said every field should have a rotation of at least three crops, with four even better. More variety makes it harder for weeds, especially waterhemp, to get established, he said.

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