Mixing Ag Chemicals with Poor Quality Water Can Be a Costly Combination
May 30, 2023 Take a moment to mentally run through your planning process prior to making a herbicide application. Chemical selection, equipment setup, and field scouting are all essential to effective weed control.
But where does water quality rank on your list of pre-application priorities? Ideally, it’s near the top, given the detrimental effect that mixing poor quality water with costly chemicals can have on equipment efficiency and herbicide efficacy. Water hardness, bicarbonates, salinity, and pH can influence how effective and economic you are in combatting a waterhemp or Palmer amaranth invasion.
“There is growing awareness that certain herbicides, and glyphosate in particular, can have reduced efficacy when mixed with poor quality water,” says sprayer expert Tom Wolf, co-founder of the website Sprayers101.com.
We’ll explore effective testing methods and treatments in my next post, so stay tuned. But let’s start by understanding what causes poor water quality and how it can cost us yield and equipment efficiency.
Mixing hard water with herbicides can soften their effectiveness in controlling invasive weeds. But glyphosate is particularly sensitive to hard water rich in iron, calcium, magnesium, potassium, and sodium ions. The positively charged cations in hard water bind with the negatively charged glyphosate molecules, which weakens the weed-killing ability of the chemical.
Given that many of us have paid at least twice as much for glyphosate during the last few years, the thought of investing more money for less return due to poor water quality is concerning.
“In the past, farmers with hard water problems often spent more on glyphosate and increased the application rate as a solution,” Wolf says. “Today, farmers can’t afford the same approach, and in some cases, have reduced their rate of glyphosate application because it’s been too expensive.”
While some might save a few dollars on front-end weed control, ultimately, Wolf says they could end up paying the price in lost yield and persistent weed problems. “Allowing heartier, more tolerant weeds to survive may speed up development of polygenic resistance,” he says. “This means that subsequent weeds of the same variety will become more and more established and herbicide resistant over time.”
The problems that poor water quality can create aren’t only in the field. For example, hard water can make some herbicides more difficult to mix or leave a “gummy” residue in the sprayer tank, says Wolf.
“Think of it like shampoo. You want to get a good lather going which can be difficult with hard water,” he says. “It’s the same with your tank mix, where hard water will make it more difficult to get a complete mix.”
One problematic scenario Wolf sees is when farmers mix cold water high in bicarbonates, with Liberty and clethodim plus Amigo, the registered activator in Canada. The combination can create an oily residue.
“If you’ve got pulse width modulation (PWM) solenoid valves, that residue may require you to physically take apart and clean each of those,” Wolf says. “An average sprayer has 72 of those valves, so poor water quality can cost you a lot of maintenance time and sprayer performance.”
Mixing turbid water containing clay particles or other suspended solids with herbicides like glyphosate can also reduce potency and create dust in the sprayer tank.
Now that you know the effects that poor water quality can have on your farm, next month we’ll look at proven methods for testing sources and treating causes.
Until then, I’ll leave you with a few figures compiled by Wolf and the Sprayers101 team on water quality thresholds to consider before your next chemical mix:
- Water with a pH between six and eight is safe to use in your spray tank.
- Total water hardness should be below 350 ppm for low rates of glyphosate (the equivalent of a half-liter per acre), and below 700 ppm for the higher rates, according to Bayer.
- EC values less than 500 µS/cm are considered safe. For values above 500, a hardness test is necessary to confirm the presence of antagonizing cations.
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