You’ve got the sprayer ready and brought the right chemical home. Now make sure your water is right for the job
Before filling up the sprayer, you may want to check your water quality.
Dr. Les Henry says some farmers might not know that hard water is affecting herbicides because they’re still getting a kill. But it may be that the chemical is “a lot less zippy than it could be if they were using good water.”
Henry is a former University of Saskatchewan professor and extension specialist and a longtime Grainews contributor. “The big thing is just keep away from the hard water,” he says.
Hard water, with high magnesium and calcium levels, is common in Saskatchewan because many wells tap into glacial deposits. Glyphosate binds to magnesium and calcium and becomes inactive.
Farmers, custom sprayers and crop consultants can purchase Hach kits from water well supply stores to measure hardness in well water, dugouts, and sloughs. A water well analysis should assign a value to hardness as well.
As a guideline, water with 20 grains per U.S. gallon is too hard to use with low glyphosate rates, and 40 grains per gallon isn’t recommended for high glyphosate rates. Water with 35 grains per gallon also renders 2,4-D amine nearly useless. But 2,4-D ester isn’t affected by hard water.
Finding an ideal water source to mix with glyphosate isn’t always possible.
“If you have shaky water, the less volume you use the better. Now, if you’re in some kind of situation where coverage is important or something like that, that might be another issue. But the higher volume results in more antagonism,” says Henry.
Farmers using hard water should not cut glyphosate rates.
Water and ammonium sulphate
Mixing ammonium sulphate fertilizer (21-0-0-24) with tank water is also an option to neutralize hard water. The ammonium sulphate binds with minerals in hard water, allowing glyphosate to do its job. Henry says the Saskatchewan Wheat Pool used to sell ammonium sulphate to use in sprayers. But he doesn’t recommend using sulphate fines, as they may contain other materials that would cause problems.
Henry says the practice doesn’t seem to have caught on.
“It’s another fussy thing to do. You’re probably better off to look for a better source of water. But if you don’t have any of that, that’s an option.”
Ken Sapsford is a research assistant at the University of Saskatchewan’s department of plant Sciences. He says if farmers are going to use ammonium sulphate, they should add it to the water before mixing in glyphosate so it can bond with the minerals.
Before glyphosate resistance was an issue, farmers were told to add more glyphosate to their tank mixes. The extra glyphosate tied up the minerals, letting the remaining active glyphosate do its job.
“And then as the price of glyphosate came down, it was cheaper just to add more glyphosate than to mess around with the ammonium sulphate. So therefore that basically overcame any issue with hard water, by just increasing the rate of glyphosate that was in the mix,” says Sapsford.
Using ammonium sulphate would allow farmers to use less glyphosate, but Sapsford cautions that ammonium sulphate won’t help with glyphosate-resistant weeds.
Farmers in the United States routinely add ammonium sulphate to herbicide mixes to break down the wax coating on leaves and get better herbicide infiltration. But Sapsford says these additional benefits haven’t been completely proven scientifically.
Some products do require ammonium sulphate in the tank mix, Sapsford says.
Other water quality issues
Although hard water is one of the most common water quality problems affecting herbicide applications, it’s not the only one.
Wells that tap into bedrock aquifers usually contain soft water, but that water might contain bicarbonate. When water contains high bicarbonate levels but low levels of other anions such as sulphate and chloride, it can interfere with the following herbicides:
- 2,4-D amine (but not ester)
- Tralkoxydims such as Achieve
- Sethoxydims such as Poast
- Clethodims such as Select and Centurion
Bicarbonate levels as low as 500 parts per million can interfere with herbicide effectiveness if herbicide rates are low, if it’s applied late, or in poor growing conditions.
Farmers who can’t avoid using water with more than 500 ppm of bicarbonate should use the maximum rate of herbicide. Herbicide should be applied when weeds are at the optimum growth stage.
Henry says bicarbonate water is rare in Saskatchewan, but there is some in the Unity and Judith River area. Southeastern Saskatchewan has the most bicarbonate wells. Manitoba doesn’t have much bicarbonate water, either, but wells in the Interlake region and southern Manitoba might hit fractured shale aquifers with high-bicarbonate water. High-bicarbonate wells are common in Alberta.
Slough and dugout issues
Sloughs and dugouts can have water quality issues, too.
“The problem with sloughs, they can be anything. They can be really pristine, or they can be a real mineral-laden thing,” says Henry.
Suspended silt and organic matter can inactivate several herbicides, including:
- Diquats such as Reglone and Reward
- Paraquats such as Gramoxone
Farmers should only use clean water when mixing these products. Dust flying up during spraying, and covering plant surfaces, can also reduce control.
Dugouts aren’t always filled with run-off, either.
“Any time a borrow pit is cut below the water table, you’re going to have water in the dugout that’s groundwater,” Henry says.
Generally, farmers should avoid using water from sloughs or dugouts ringed by salt. Water with nothing growing in it might be too salty to use in tank mixes. Water bodies that fill up without rain, and stay full through the summer and through dry periods, are likely drawing on groundwater and should be avoided as well.
Eyeballing a dugout or slough’s salinity isn’t an easy task. Water that looks fine may be too salty. Farmers who rely on crop advisers can ask them to measure the electrical conductivity to get an idea of salt content.
Electrical conductivity, measured in microsiemens per cm, can also reveal how hard water is. If the water only runs through glacial deposits, dividing the electrical conductivity by two produces hardness in parts per million. Dividing electrical conductivity by 35 yields hardness in grains per gallon. Water with less than 500 microsiemens per cm isn’t likely to affect any herbicides.
Henry says if a farmer has been using a dugout for a while and it’s working ok, it probably doesn’t need to be tested.
“But if they’re starting in a new dugout, just because it’s clean doesn’t mean that it might not have a lot of minerals in it.”
For more information, check out Saskatchewan Agriculture’s Water Quality and Herbicides fact sheet. This article also references Les Henry’s Henry’s Handbook of Soil and Water. †
— Lisa Guenther is a field editor with Grainews at Livelong, Sask. Follow her @LtoG on Twitter.