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‘Know Your Enemy’ is a big draw

By Staff | Aug 25, 2015

-Farm News photos by Michele Linck A GROUP GATHERS on a slight rise to listen as Iowa State University Extension crops specialist Joel DeJong explains more about the ongoing trials involving weeds, including this soybean field’s infestation of volunteer weeds, at the experimental farm at Sutherland.


SUTHERLAND – Keeping the weeds from stealing moisture, nutrients and sunlight from the crops is a major chore for farmers throughout the growing season.

“Know Your Enemy,” a weed-fighting field day held Aug. 5, drew 33 farmers to the Iowa StateUniversity Northwest Iowa Experimental Farm to learn more about dealing with weeds, along with field conditions and the timing of herbicide applications.

The turnout for the morning session for farmers was twice what ISU Extension field agronomists Joel DeJong and Paul Kassel said they had expected.

DeJong said the attendance showed how serious farmers are about combating weeds and the yield losses they cause.


Producers have to be prudent in how much they spend to kill or deter weeds and still come out with a profit, DeJong said. Proper timing and the right product on specific weeds are crucial to the cost effectiveness of any weed program.

Prior to touring the farm’s weed plots, which were planted with soybeans, but not treated for weeds, DeJong and Kassell issued a form and asked farmers to record what chemicals/herbicides they used, the active ingredient in each, the amount they used, its application rate and its active ingredient rate for each of the past two planting seasons.

The sheet included examples of the algebra needed to do the comparisons.

Few attendees dug right in to record their data.

It was a bit of a gotcha moment.

DeJong said the point was that a farmer can tweak, or abandon, any weed program, but not if they don’t recall the program’s data.

In effect, heysaid, farmers start over each year.

Keeping detailed written records is the only way to know and remember that information.

“So, write it down,” DeJong said. “It yields invaluable guidance over the years, to know what worked and what didn’t, and how it performed in the predominant weather conditions of each year.”

Field trip

By late morning, Kassel, DeJong and farmers were walking among several of the farm’s weed plots in which soybeans faced competition from a spectrum of naturally occurring weeds.

With no herbicide progrm, the weeds dominated bean fields, growing unevenly dense in each plot, challenging the soybeans throughout the patch.

The plots’ slightly lower corners had collected the most weed seed, including tall, thick clusters of Palmer waterhemp.

A single waterhemp plant can produce more than a hundred thousand seeds, and huge losses for crops. The right herbicide is vital, DeJong said.

“Five years ago,” he said, “we had people who doubted we had a (waterhemp) problem.”

Kassel noted that waterhemp is resistant to herbicides in groups 2, 3, 5, and 22 – so what is left?

“There is no magic bullet,” DeJong said, “so we have to keep these groups working.

“Do we want to ride that horse until it’s dead?” he said of RoundUp.

Richard Nedved, who farms near Pocahontas, said he attended looking to learn more about waterhemp’s herbicide resistance.

“I learned how to attack (waterhemp) with more than one mode of action,” he said, “to use two or three.”

Steve Wachtel, of Melvin, said he farms only grain on his farm, founded in 1887, and that waterhemp resistance is giving him trouble.

“Paul and Joel did a wonderful job, excellent handouts,” he said of the field day.

And, Scott Engelke, of Paullina, said he still includes cultivation as a way to keep the weeds at bay.? Giant foxtail: not resistant to RoundUp.

  • Barnyard grass: all kinds of resistance.
  • Common cocklebur: some resistance to glycosphate.
  • Velvetleaf: used to cause fear (leaves as big as a pie pan).

Other include: snakegrass, ragweed and nightshade.

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