If I were asked to choose a favourite old adage about farming, I’d make up any excuse to avoid doing so. If pressed further, I’d offer up a classic such as “The cure for high prices is high prices.”
As adages go, that one has it all: a caution to make hay while the sun shines, shaped by the old saying that what goes up must come down, wrapped up in the fable of killing the golden goose, all in the glow of 20-20 hindsight.
Read Also
Beef demand drives cattle and beef markets higher
Prices for beef cattle continue to be strong across the beef value chain, although feedlot profitability could be challenging by the end of 2025, analyst Jerry Klassen says.
To be sure, high commodity prices can also be “cured” by market forces outside of farmers’ ability to foresee or control, not just by a surge of supply that leaves flooded markets and broken crop rotations in its wake. But as narratives go, a victim of his or her own success is much more irresistible.
For me, that’s what made great reading out of a new data-mining study led by researchers from the U.S. Department of Agriculture’s Agricultural Research Service (ARS) and published last month under the title “The silver bullet that wasn’t.”
The study goes deep into herbicide evaluation data gathered between 1996 and 2021 at university soybean and corn plots in nine U.S. states and southern Ontario. It re-crunches all that data to chart the level of control glyphosate showed over time against seven weed species: Palmer amaranth, tall waterhemp, ragweed, giant ragweed, lamb’s quarters, Canadian waterweed and velvetleaf.
You’ve already guessed where this is headed, but here goes: the study further breaks out the data to show the level of weed control over time from a treatment plan that includes a single in-crop application of glyphosate after a soil-residual application of another herbicide. The study then compares those numbers against the level of weed control provided by just a single in-crop hit of glyphosate.
The result? More charts than we have space to show here. In summary? The sites that relied solely on foliar applications of glyphosate show significant decreases in weed control over that time span. The sites that had pre-treatment with another herbicide, followed by in-crop glyphosate application, showed more consistent control over those same years, and even slight increases in control in some cases. The weighted regression charts for weed control relying solely on glyphosate pointed generally downward. Not straight down, mind you, but in most cases, the downslopes on those charts are steep enough for a nice afternoon of sledding.
More charts in the same study show the variability in weed control provided by those treatments — that is, how much the weed kill count deviated from the mean. Again, the sites relying solely on in-crop glyphosate for weed control showed increasing variability over time; the pre-treatment/in-crop combo sites showed little to no variability. And the upward slopes on the charts for the glyphosate-only sites over time are even more impressive from a tobogganing perspective — that is, if you were to start in 2021 and ride that sled back through time.
As the researchers put it, “when used alone, glyphosate efficacy decreased and became more variable” and “the adaptation of seven key weed species to a single, widely adopted management practice in North America was rapid.”
It goes to show, they said, that “the short-lived success of glyphosate for weed control in North American corn and soybean production systems is a testament to the importance of incorporating diversity into current and future weed management systems.”
Indeed. I could be smug and say I saw all this coming — or I could be much less smug and say I saw people who saw it coming — back in the late ’90s, when Roundup Ready cropping systems were introduced. Those new systems were certainly a boon for adopters of reduced- and zero-till — and the ability to control weeds with a quick hit of a broad-spectrum herbicide, rather than multiple applications of selective chemistries with heavier environmental impacts, looked like a no-brainer.
But as it became clear how ubiquitous the RR systems would be, I heard from farmers who feared the resulting increase in glyphosate use — rather, its sole and/or continuous use and abuse — would render glyphosate obsolete sooner or later. On the other hand were enthusiasts assuring us glyphosate resistance was a non-issue — because unlike the selective herbicides that weeds were already adapting to resist at the time, glyphosate would kill everything.
Seeing as the Roundup Ready system’s existence is based on plants that glyphosate will not kill, that was a peculiar assurance at best. But what did I know?
See, in its defense, back then if anyone were to have put money on the herbicide least likely to face resistance over time, it would have been glyphosate. In the 22 years before Roundup Ready crops came along, no one knew of any plants with adapted or natural resistance to that herbicide. Plus, given glyphosate’s specific mode of action and its non-selective nature, the chance of weeds mutating to beat it was believed to be extremely remote.
But beat it they have. The International Herbicide-Resistant Weed Database today shows 59 species of Group 9-resistant weeds worldwide. Of the 59, eight have been seen in Canada. Of the eight, two — kochia and downy brome — made their Canadian debut on the Prairies.
The new study’s authors say continuous use of glyphosate over time “exerted intense selection pressure on weed communities to adapt” to the product. Put another way: the effectiveness of glyphosate-tolerant cropping is gradually being cured by its commercial success.
New tactics
How do we cure the cure? As the study’s authors say, “incorporating diversity” back into these cropping systems is certainly a start. Slowing the rate of weed adaptation calls for more “biological, cultural, and mechanical tactics,” along with changing up our herbicide choices. We’re also now well acquainted with the stacked-trait herbicide-tolerant seeds meant to expand growers’ spraying options — but those aren’t the focus in this study.
“Rather than exclusively seeking the next silver bullet product to solve weed control issues, these results illustrate the need for additional weed management strategies in order to protect the efficacy of current herbicides and provide higher and more consistent weed control,” the study says.
To all that I can only add: who’d use an actual silver bullet anyway? How did that become the term for a cure-all favoured by people seeking blunt instruments against complex problems? Because it works on werewolves and vampires in movies and comic books?
Pfft. That just presupposes those legendary creatures of folklore wouldn’t learn to reduce their risks over centuries of evolution — and that’s the sort of detail one misses when one leans too heavily on quaint clichés.
Which is why you don’t want to ask me to choose a favourite old adage about farming.
