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Water quality can change after a drought — and that can affect the efficacy of your herbicides.

“It’s well known that there are certain things in water — chemicals, salts, metal cations — that can antagonize the spray,” said well-known spray expert Tom Wolf. “With much lower water levels, it’s conceivable that those antagonists will have possibly increased in concentration.”

Not only could herbicides be less effective due to water changes, producers are also facing a potential shortage this spring.

So book water tests as soon as possible, advised Wolf, a partner in Agrimetrix, a Saskatoon company focused on agricultural spraying.

“First thing we do, is we take a water sample and look at it,” he said. “We’re just looking for clarity.”

Turbid water, or water with solids in it (usually clay), can antagonize glyphosate — a process where a herbicide is rendered less effective.

“The herbicide is so highly polar that it is attracted to those little tiny soil colloids. They tie it up, they don’t want to release it,” he said.

Hard metal cations are the best-known antagonists, and can be measured by using electrical connectivity. Electrical connectivity meters are reasonably inexpensive but unfortunately, they can’t tell you what is in the water.

Tom Wolf.

photo:
Supplied

“We’re looking for a number that might be cause for further investigation,” said Wolf. “If it’s a number of 500 or less, it really isn’t a problem.”

But if the reading is higher than 500, Wolf first looks for bicarbonates.

“Bicarbonates are parts of most waters that can bind to some herbicides and they get less active,” he said. “The most important group of herbicides involved are the Group 1 herbicides, which include grass killers, wild oat herbicides in cereals and all sorts of oilseeds.”

If bicarbonate levels are high, the solution is to add some ammonium sulphate, he said.

Hardness is another issue, and there are five hardness cations (which have a positive charge) that can bind to weak acid herbicides.

“Almost all of our herbicides are weak acid,” said Wolf. “The degree to which they are interfered with depends on the herbicides. Glyphosate, the most commonly used herbicide in Canada, is most susceptible to it.”

The most common hardness cations are calcium and magnesium, followed by sodium, potassium, and iron.

“All five of those antagonize the herbicide at different degrees,” he said.

With a hardness measurement of 500 parts per million or more, “you should probably condition the water,” said Wolf.

However, hardness is calculated from just calcium and magnesium but other elements, such as sodium or iron, could also be present in significant concentrations.

They “don’t figure into this equation, and yet they contribute to hardness, or antagonism. And so that’s why we look at each of these ones individually,” he said.

What to do

With a parts-per-million reading, “we can pretty much predict how much damage they might do and how much conditioning the water needs,” Wolf said.

Herbicides are designed to fit into enzymes and make them inactive, but when a cation interferes with the herbicide, it stops that process.

If your lab test comes back with evidence of hard water, there are several things you can do.

“If it’s too hard, you can look for a better source of water,” said Wolf. “If it’s surface water like a pond or dugout, it probably won’t be hard water and will probably have other kinds of issues, like turbidity.”

Hard water is more common for subsurface water, such as wells.

“Different aquifers in the province have different hardness. Even on the same farm, if you drill a different well, you may tap into different aquifers and get two different water qualities. I’ve definitely seen that on farms.”

If a better water source isn’t available, it’s possible to condition the water with a chemical additive — or increase the herbicide rates.

However, Wolf doesn’t necessarily recommend increasing herbicide rates (especially when there are shortages) because it’s costly and there are conditioning options.

“Ammonium sulphate is a well-known water conditioner that helps cure the hard water problems,” he said. “Basically, there are recommendations for different water hardness and how much ammonium sulphate you should add to the water.

“You fill your tank half full of water, you add ammonium sulphate, agitate and it dissolves quite readily and then you add your herbicide and then you top it up to finish.”

Using a formula developed at the North Dakota State University, a producer can determine how much ammonium sulphate is needed. (For more info, see this article at Wolf’s Sprayers 101 website: www.tinyurl.com/4mb779sy.)

“If we know the parts per million, we can pretty much predict how much damage they might do and how much conditioning the water needs,” he said.

There are some other products available, but Wolf doesn’t recommend them. For example, citric acid can be used, but it changes the pH of the water.

“You can get a real mess if you don’t know what you’re doing. Acidifying the spray mixture can help some herbicides, but it can really hurt others and you have to know which is which.”

When there’s a shortage or when the cost of a herbicide skyrockets, the temptation is to reduce the application rate.

But don’t do that blindly, said Wolf.

“When you shave rates, it’s really important to look after water quality,” he said. “It’s really a concentration issue. Your water quality is constant and it’s a molecular ratio. If you put fewer herbicide molecules in there, the molecules in the water will overpower that.”

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