80 percent mature heads ideal time for pre-harvest glyphosate

Standing crops were barely standing Sept. 9 in the Pincher Creek, Alta., region after wet snow fell across the southwestern part of the province. | Tracy Glen photo

Standing crops were barely standing Sept. 9 in the Pincher Creek, Alta., region after wet snow fell across the southwestern part of the province. | Tracy Glen photo

I had an interesting question from a grower this week. The question was “What is the operation that if I screw up, costs me the most money?”

Basically, he was asking for an evaluation of his practices and suggestions on how he could improve. This is different from most questions from farmers.

Most want to know ‘What more can I do?’ rather than ‘What can I do better?’

I had to step back and give the question a little thought. The answer that would have rolled off my tongue, had I not known this grower would have been “Spraying herbicides too late.”

However, I have worked with this grower for a number of years and we had been down this road a number of years ago.

He sprays in a timely manner and, barring adverse, weather, completes his cereal herbicides by the four leaf stage and has both canola applications done before the cabbage stage.

So what other practices could he improve?

The number one place where farmers have hurt their yields over the past 10 years is, from my vantage point, preharvest glyphosate timing.


Early application will cause yield reduction, reduce bushel weight, kernel weight, protein and in extreme cases, reduced grades.

Early applications may also result in residues in the seed. Maximum residue levels (MRLs) usual target is to apply glyphosate at 30 percent moisture.

So what does this look like? Generally, the wheat crop must be in the hard dough stage. This is when the kernel has become firm and hard and a thumbnail impression re-mains on the seed. It is also the stage when the final weight of the kernel has been determined.

The other way of determining the proper staging is when the wheat reach physiological maturity. This stage can be determined when the peduncle changes from green to tan.

So this seems quite straight forward. However, there are a couple of complicating factors.

First, many fields are uneven this year. In many situations, one area of a field may be ready for pre-harvest application and other areas still immature.

The second factor is tillers. De-pending on growing conditions, planting density and varieties, tillering can be extensive. Tillers may come later in the season when some rain follows a dry period.


So how do you determine when the proper stage has been reached? The key is to get a representative sample of a field. I sample 10 areas of a field. I walk into a field past the headlands, double seeding and double fertilizer may give misleading information, and grab a handful of stems.

I examine each head and determine if it is physiologically mature. I then note the total number of heads examined and the number that are mature, for example 33/28.

After repeating this in the other nine areas, I tally the numbers and come up with a percentage of mature heads.

The number that I look for is 80%.

If there is a large area in a field that is immature, you may wish to spray only the most mature area and follow up in a week or so to pre harvest the remaining area.

Remember, you can’t rely on the colour of the field as an indicator.  Walk the field and sample representative areas to determine pre-harvest staging.


Thom Weir is an agronomist with Farmer’s Edge. He can be reached by emailing thom.weir@farmersedge.ca.

  • Dayton

    Great, let’s be sure at least 80% of the wheat is chemically laden prior to milling it into bread. Who says it’s 100% gone? You wonder why breakfast cereals are taking a backseat to yogurt and other organic products?

  • We get no protection from Health Canada. This practice should be banned. We are on own. The best thing you can do is get educated on the harmful effects these pesticide -laced grains have on your autoimmune system ( eg.Celiac disease and gluten intolerance) and your brain (Alzheimer’s disease) It is even in babies formula, for gawd’s sake. Be a conscientious consumer. Don’t buy GMO Roundup Ready grains.

  • Daeran Gall

    It is news like this that fuels the demand for organics. Is this practice damaging to the marketing of wheat with high glyphosate residues.


  • Neil

    it is unfortunate the three responses above do not do more research before jumping to conclusions. Glyphosate translocates to the roots of the plant and the author is telling producers not to spray too early so there isn’t unsafe residues left in the grain. Not only does Health Canada test this practice before it was allowed in Canada but so does Agriculture Canada, Environment Canada and Fisheries and Oceans department. We producers don’t use a practice unless it has been scientifically proven to be safe in the food supply.There are no GMO grains (wheat, barley, oats, rye, etc.) or pulses, only canola, soybeans, and corn in Canada. Lastly the practice doesn’t leave high glyphosate residues. It doesn’t hurt our wheat marketing because it is approved all around the world, including Europe (where it was first used) who is known as the most safety conscious consumers. Please don’t believe all the fear mongering that you are spreading.

  • Dean

    Excellent article Thom. I am so sick and tired of these uneducated, tree hugging fools who never quit about “harmful chemicals” that us farmers are using. A connection between glyphosate and all those GI diseases? That’s rich. Let’s see the evidence based medicine on that one. You won’t, because it doesn’t exist. Producers don’t use these products because we “want” to. They are very expensive. Without them our fields would be ridden with disease, weeds and insects. There would be no yield not to mention the very poor quality. Maybe the above authors would be happy going into a grocery store and paying 20 or 30 times more for the food they buy. The best thing they can do is get educated, maybe set foot on an actual farm for once and talk to producers. The rest of the 99.9% of consumers in Canada and the world are very happy with Canadian Ag Products. Perhaps the answer which is just as intelligent as the above comments, is to just quit eating all together.

  • richard

    You will notice that the “church” never promotes the use of glyphosate on barley? That is because roundup destroys the viability (lifeforce) in the seed….If you can’t sprout barley, you can’t make malt. The maltsters wont touch it…..Wheat and durum…. who cares….the “great unwashed” will eat everything, agrotoxins included…..and so goes the dizzy decline of critical thinking…..and oh yeah….our healthcare system…..

  • Dirk

    I think the only reason I’ve turned slightly towards being pro gmo is because activists drive me crazy. Spraying glyphosate in the fall helps me have clean fields, glyphosate and many other chemicals are and important part of my intergrated pest managent and also my to feed more people safely. I would like to start an anti organic movement but I have not time for that.

  • richard

    Interesting when critical thinking is forfeited to blind faith in technology how certain glib platitudes get continually rolled out like mantras…..”scientifically proven safe”, “organic fields ridden with disease weeds and insects”, “feed the hungry planet” and so on….ad naseum. The simple reason organic food is a $60Billion USD international trade is because educated people dont believe agribiz dogma. Reality speaks to watersheds contaminated by the hubris of industrial agriculture, disease and insects being perpetuated, not mitigated by technology……and the “world being fed” delusion, looking a bit like a dog chasing its tail……The consequence to society is a collective “unhealth”….but of course that has nothing to do with the air we breath, the water we drink or the food we eat…..Better living through denial is the order of the day….

  • neil

    That is a new one, bringing religion in to justify why an agriculture practice is wrong. Not sure why a religious person cares about malt but that is another story. In fact researchers are looking at preharvest glyphosate on malt barley. Its all about timing as the story author explained. If “agrotoxins” are in our food why are there no reported deaths from it, why are we living longer and why does our health care system work so well for our society?

    • richard

      I guess you miss the point…..Agriculture has become largely a faith based religion, the production technix of which are almost entirely proprietary and passed on to producers at great cost in the “faith, hope and belief” that profitability will follow….When it works the results are spectacular…..when it fails the proponents run for the hills (BST, BSE, CWD, CJD, herbicide and pesticide and disease resistance, watershed contamination with nitrates ,phosphates, pharmaceuticals, and pesticides)… and society is left to clean up the mess. The WHO has predicted that if current trends continue that in next twenty years the cost of administering healthcare will break governments. And the largest cost of healthcare is not hospitals or even doctors but what? Pharmaceuticals… If your world view is simply the success of glyphosate on your wheat it is understandable why the big picture eludes you…..It requires a colossal suspension in critical thinking to believe there is no connection between agriculture, the environment and a hundred new degenerative health disorders prevalent in modern culture…..

  • Agrichemical companies and the biotech industries have done an AMAZING job of selling their products to North Americans. By lobbying government officials, with all kinds of deals, they get approval, with their half-baked studies, to release their latest and greatest GMO seeds and more potent pesticides into OUR environment.
    Many farmers tend to believe the “scientifically proven to be safe”propaganda and tend to use and overuse these products. They are caught up on the chemical treadmill. It is wildly profitable for the agrichemical companies and biotech industry. Meanwhile, the farmer is, quite literally, losing fertile ground.
    On the other side of the world, the truth is coming out about the harmful effects of GMOs and glyphosate from unbiased (not on the payroll of Monsanto et al.) reseachers.
    Even in America, there are scientists trying to get the truth out but are often subverted by the moneyed major players.
    Consumer are increasingly questioning this method of food production and are looking for more healthy options. We don’t care how weed-free a crop is or how much easier it is to harvest a dessicated (Roundup Ready) crop, we just want to be able to buy nutritious,chemical- free, healthy food for our families.
    “Chinese and International Experts Slam GMOs and Glyphosate Beijing Conference” in July 2014 explains the OTHER side of the story. Who should we believe, agro-giants or independent researchers?
    Google: Chinese and International Experts Slam GMOs and Glyphosate at Beijing Conference – Sustainable Pulse.webarchive

  • Dayton

    Producing more Feed and Fuel does not constitute extra food production or an excuse to use more chemicals. That’s Chem/Corps way of telling you to increase their bottom line. Don’t get sucked in. More production equals less profit (supply and demand), sorry if you don’t understand that concept. Stay on the treadmill it will always produce the same results.