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Oats not affected by pre-harvest glyphosate

Despite buyers’ concerns, variety and environment have more impact than glyphosate

In the spring of 2015, Grain Millers announced they wouldn’t buy oats that had been treated with pre-harvest glyphosate. Christian Willenborg was alarmed.

“I was alarmed because I really hadn’t heard of an issue. I hadn’t seen an issue,” said Willenborg, assistant professor at the University of Saskatchewan and editor-in-chief of the Canadian Journal of Plant Sciences.

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“So I kind of dug into the data and I can tell you the literature’s silent on this, folks.”

That knowledge gap inspired what Willenborg called a “look-see” experiment.

The experiment

Willenborg and Nancy Ames, cereal researcher with Agriculture and Agri-Food Canada (AAFC), presented findings from a preliminary experiment examining pre-harvest glyphosate treatments on oats.

The study was done at two locations near Saskatoon, with four replications at each site. Researchers used two cultivars, CDC Dancer and AC Pinnacle.

Researchers measured the results of three different harvest systems:

  • swath at 35 per cent seed moisture;
  • direct harvest, no glyphosate; and,
  • direct harvest with a pre-harvest glyphosate treatment. It was applied at 30 per cent seed moisture at the label rate.

Researchers then measured the effects of different harvest systems on everything from test weight to milling quality. They also worked with the Canadian Grain Commission to test glyphosate residue.

Effects on yield, kernel size

The harvest systems’ effects were consistent with both oat varieties.

The swathing system saw an 18 per cent yield drop, Willenborg said. He explained they used a plot swather, which tends to lay down a poor swath in cereals. They won’t use that swather next time, he added.

“I don’t expect your yield reductions will be as great (with swathing).”

Willenborg said there was no adverse effect on yield with the glyphosate application. In fact, they saw a slight yield bump and significantly greater test weight, he added.

Researchers also found 40 per cent fewer thin kernels in the glyphosate system relative to the swathed oats. Both direct harvest systems produced more plump kernels than the swathed oats.

Researchers did detect glyphosate residue in the oats that received a pre-harvest treatment. But it was only four parts per million, which is well below allowable levels.

Willenborg noted the Canadian Grain Commission now has a glyphosate residue test for oat samples. “And we’re going to work with them and continue to send these samples in.”

While the results are preliminary, researchers found that harvest systems do affect physical quality.

“But in no instance did we see that the pre-harvest application of glyphosate had any negative influence on physical quality, relative to a well-timed swath or direct cut,” said Willenborg.

Effects on miling quality, flake quality

Ames said that in her lab “we tried to look at those quality characteristics that we thought would matter to grain millers, to others. Will this affect our marketability eventually?”

None of the harvest systems affected nutrients such as beta-glucan and protein, Ames said. But, unsurprisingly, growing location and variety did.

“These are different varieties. We expect beta-glucan to be different. These are different locations. Protein is always affected by location. Beta-glucan is affected by location,” said Ames.

Researchers also looked at oat pasting viscosity. A lower score means the oat flour will be less desirable for puffing and extrusion, Ames said. “The glyphosate treatment is no different than the straight combining. It’s exactly the same. But the swathing is considerably lower.”

All three harvest systems produced oats with similar groat breakage metrics, Ames said. The glyphosate treatment produced oats that were slightly better for milling yield, she added. Milling quality was similar in the glyphosate treatment and the other direct harvesting system.

Ames said they’d anticipated a difference with water absorption, which is one measure of flake quality.

“We do see some differences in flake quality with respect to the varieties and location, but not with the harvest treatments,” she said. Flake colour was also the same across harvest systems.

The bottom line is that variety and environment affected quality more than pre-harvest treatments, Ames said. Using glyphosate before straight combining resulted in milling quality similar to straight combining alone, she added.

Ames said they need to do more studies to see what happens when glyphosate is applied at different moisture stages.

Future work

Willenborg said they have a much larger project planned for the future. That project will look at weed control in oats and quality. Over the next two years, researchers will again examine three harvest systems; applying glyphosate pre-harvest in a direct cut, direct cutting without glyphosate, and swathing.

Each of those harvest systems will be tested at various seed moisture contents. Researchers will measure how timing affects functional quality, particularly with glyphosate treatments.

Willenborg said they also plan to measure stand uniformity. The goal is to see whether green tillers are a factor. If there’s an issue, they’ll look at whether higher seeding rates can reduce problems, he added.

The work around these studies has been funded by the Saskatchewan Oat Development Commission, the Prairie Oat Growers Association, and the Agriculture Development Fund.

A few caveats

Both Chris Willenborg and Nancy Ames noted the study was preliminary. “I caution the interpretation, because it is done just in a single year,” said Willenborg.

It’s also important to remember that research- ers followed the label when applying glyphosate before harvest.

If farmers go off-label, “that’s a black hole,” Willenborg said. “We don’t have data on that. We’re going to work on it. But at this point, if you’re doing everything by the book, so far we don’t have any indication that suggests there would be an issue there.”

The Prairie Oat Growers Association’s website also reminds farmers to follow the label when applying glypho- sate. If it’s applied pre-harvest when kernels are green (30 per cent moisture or better), farmers risk residue in the kernels that tops the limits. Farmers can avoid this by making sure the least mature parts of the field are below

30 per cent moisture. The association also notes that some customers have their own restrictions on pre-harvest glyphosate.

Willenborg also noted that the World Health Organization has declared glyphosate a possible carcinogen. Farmers and industry need to be aware of that designation, and consumer perceptions, going forward.

And finally, Willenborg reminded farmers that each additional use of glyphosate carries risks. “Most of our quarter sections are probably seeing two applications minimum per year.”

The United States has seen a 10- to 12-fold increase in glyphosate use over the last two decades, Willenborg said. Some States have 10 to 12 glyphosate-resistant weeds. And Western Canada is now seeing glyphosate-resistant weeds as well, he noted.

About the author

Field Editor

Lisa Guenther is field editor for Grainews based at Livelong, Sask. You can follow her on Twitter @LtoG.


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  • Yes Maam

    Only 4 ppM of glyphosate residue on oats? It only takes 0.1 ppB to destroy gut bacteria, which is where 70% of the immune system lies. It took only 0.1 ppT of glyphosate to stimulate the growth of breast cancer cells. It take very tiny amount to cause endocrine disruption which can lead to sperm death, birth defects, infertility, sterility and miscarriages. If you care about babies, about life, you will trust in God and Nature and stop using glyphosate based herbicides.
    The FDA found 1.67ppm of glyphosate residues on oat baby food. If a baby ate just 3 oz of that food, 4 x a day, it would be consuming 15,000 more than the rats in Antoniou’s study which contracted non alcoholic fatty liver disease, in one day. 1 in 10 Americans now hove NAFLD.
    Farmers have been told glyphosate based herbicides are safe, but they are not. Please stop believing the lies. Trust your farming ingenuity. Stop using toxic chemicals. Farm organically.

    • P_B

      Since your name doesn’t imply scientific credentials, can you please provide links to the actual studies you are citing? Specifically “.1 ppB to destroy gut bacteria” and “FDA found 1.67 ppm of glyphosate residue.” And I want links to the actual studies not links to environmental/mommy blogging websites, as these tend to be circular. My googling isn’t coming up with what you are citing. In fact “Antoniou” connects to a pizza parlor and in three pages never got to a scientist so I quit looking.

      • Yes Maam

        Yes. has scientific studies from Carrusco and Kruger showing destruction of guy bacteria. And there is an article by Carey Gillam which reveals that the FDA tested baby oat meal and found 1.67 ppm.
        Look up Michael Antoniou UK scientist and liver disease, NAFLD.
        If you are one to automatically discredit mom blogger websites, consider that you are being mysogenistic. Without mom’s instinct to protect their family, none of us would be here. Our ancestors would not have survived harsh weather, poison foods, illness, and migration. Listen to the moms. They are the experts in our children’s health, and our children literally are our future. You want a powerful, success country? Listen to the moms.

        • P_B

          When I was in high school I got a lot of red ink on a paper for making assertions where I had no expertise without citing a reference. That is called opinion. I wasted a half-hour this morning chasing these rabbits, continuous ending up with an authorative sounding citation, but without merit. So, the Moms Across America has a leading citation of a study by Newcastle College that is really a compilation of other studies purporting that organic is more nutritious for a couple of reasons. One of their citations to that information dead ends. Another citation goes to this study and that one says “there is no significant difference in nutrition but their might be to pesticide exposure!
          So, Ma’am, if you are going to throw out scientific sounding facts and want to be taken seriously by farmers, then YOU provide the links to provide scientific backing for what you asserting, don’t make us do it. Otherwise it is just your opinion.

          • Yes Maam

            I have over 60 studies…There are hundreds more on GMOFreeUSA which show harm from Glyphosate and GMOs. If you are in the business of growing food I would expect that it would be in your interest to research and read the latest info on food and pesticides you spray on our food. If you need to criticize a mom for not doing your work for you that’s not my problem. You don’t need toxic chemicals to grow food. Period. Farmers have been growing food for THOS

          • P_B

            You are the one who initiated the comments using “facts.” All I am asking for is that you provide the appropriate citation link for each of your “science facts.” Even scientists do that out of respect for each others work.

  • P_B

    I suspect the biggest problem is the use of glyphosate in pre-harvest applications. I have never been in favor of this in any grain because of the problem of residues. And the problem of honesty. We self-govern the pre-harvest interval and if it looks like rain is coming there are too many farmers that will say “screw it” and combine the field.
    My frustration with this is that No-Till depends heavily on glyphosate and this misuse of the chemical means we farmers may lose one of the best and cheapest tools we have as a burn-down chemical.

  • neil

    Gluten intolerance rates and use of preharvest glyphosate is an example of correlation, not causation, unless there has been scientific studies done that show a link of one causing the other. The same is true with your last two comments on cancer and autism. Unless there is evidence to show one is causing the other it is just an opinion not supported by facts. I agree with P_B below that I think the biggest problem is rolling land that leads to uneven crop maturity and farmers not waiting long enough on the greener less mature areas before they spray. I also agree that we farmers are overusing glyphosate.