Wallaces Farmer

How water impacts herbicide performance

How to seek alternative water sources as a herbicide carrier.

Gil Gullickson, editor of Wallaces Farmer

June 6, 2024

3 Min Read
Crop sprayer in action
READ THE LABEL: A herbicide label provides specifics on water temperature and products to add to mitigate such concerns as water hardness.Courtesy of Corteva Agriscience

Early growing-season discussions often center on scant or excessive water for crops. This year, though, talks about water and herbicide applications are intertwined.

That’s because some Iowa communities earlier this year restricted water usage. This may spur farmers and applicators to use alternative water sources for herbicide applications. Subbing treated rural water for untreated surface or well water may raise concerns about how debris or suspended solids in water and water hardness may impact herbicide efficacy.

“Something as simple was pouring water into a Mason jar can be used to check for debris or suspended solids,” says Meaghan Anderson, Iowa State University Extension agronomist.

There’s an old joke about well water being so hard you can almost hear iron chunks coming out of the pump. Seriously, at-home kits and laboratories can reveal water pH and water hardness, depending upon the preciseness of data needed. Retailers that sell swimming pool supplies offer at-home kits that are fairly inexpensive. Download this Purdue publication for more information on testing options.

When to use AMS

Much confusion reigns in the marketplace regarding AMS (ammonium sulfate), nitrogen replacement water conditioners and other additives that are marketed to mediate water hardness, says Mark Storr, BASF technical service representative. If a herbicide label says to use AMS to curb water hardness, use AMS, Storr says. In Liberty’s (glufosinate’s) case, AMS not only mediates water hardness, but also helps improve herbicide performance.

“The ammonium ion that's in AMS is actually responsible for some of the weed control that glufosinate provides,” Storr says. “When you add AMS, you provide a source of ammonium nitrogen within the weed itself and helps it kill the weed. That cannot be provided by a nitrogen replacement water conditioner.”

Glyphosate’s label also specifies the use of AMS to manage water hardness. “Glyphosate is certainly the poster child for weak-acid herbicides that can be negatively affected by water hardness,” Anderson says.

Use ‘Goldilocks’ water temperatures

Remember the children’s story “Goldilocks”? A portion of it concerns Goldilocks finding porridge that was initially too hot and later, too cold before finding a bowl that was “just right.”

In a sense, that applies to the temperature of water used as a herbicide carrier. Purdue University researchers found two Goldilocks temperatures out of four they tested that include:

  • 41 degrees F

  • 72 degrees

  • 102 degrees

  • 133 degrees

They discovered that the coldest and hottest temperatures reduced herbicide performance. Meanwhile, the two middle temperatures — 72 and 102 degrees — did not negatively impact performance. Read more in the Purdue University Extension publication “Water Temperature and Herbicide Performance: A First Look at New Research,” available as a free download.

Be careful cutting water volume

Take care when cutting water volume, because volume provides more herbicide coverage. “Bear in mind that with the postemergence products that we use nowadays, more volume is generally our friend, to an extent,” Anderson says. “When we rely more heavily on contact herbicides, coverage [through sufficient water volume] is critical to getting good control.”

In the contact herbicide Liberty’s case, use at least 15 gallons per acre, Storr says. “Twenty [gallons per acre] is better,” he adds.

What should I do if I’m still unsure?

Read the label, Anderson says. “Some labels recommend use of specific products to address certain water quality concerns, while others will prohibit certain products,” she says.

Pay particular attention to mixing order of herbicides and accompanying products, such as adjuvants and water conditioners, Anderson says. Mixing them in the wrong order can create a cottage cheese-like concoction in a spray tank.

About the Author(s)

Gil Gullickson

editor of Wallaces Farmer, Farm Progress

Gil Gullickson grew up on a farm that he now owns near Langford, S.D., and graduated with an agronomy degree from South Dakota State University. Earlier in his career, he spent 13 years as a Farm Progress editor, covering Minnesota and the Dakotas.

Gullickson is a widely respected and decorated ag journalist, earning the Agricultural Communicators Network writing award for Writer of the Year three times, and winning Story of the Year four times. He is a past winner of the International Federation of Agricultural Journalists’ Food and Agriculture Organization Award for Food Security. He has served as president of both ACN and the North American Agricultural Journalists.

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