Well, let’s start out with: What’s Roundup®?
You can read more about Roundup® HERE.
“Roundup Ready®” is Monsanto’s trade name for crops (soybean, maize, cotton & alfalfa, e.g.) that have been genetically engineered to tolerate glyphosate.
Simply put, a bacterial gene (or genes) coding for an enzyme that promotes the breakdown of glyphosate has been transferred to these plants. (You can see how HERE.)
Thus, farmers can spray Roundup® on Roundup Ready® crops, and they don’t die, because they can detoxify the herbicide.
“Glyphosate-resistant soybean was the first crop launched and marketed under the Roundup Ready brand in the USA in 1996.” (from Ref. 1 below)
Secondly, What Is A “Superweed”?
“Use of superweed has snowballed in recent years, along with considerable misinformation that isn’t supported by scientific facts. Most online dictionaries, for example, associate superweeds with herbicide resistance caused by the suspected transfer of resistance genes from crops to weeds. To date, there is no scientific evidence to indicate that crop to weed gene transfer is contributing to the herbicide resistance issues faced by farmers.”
And the official definition, from the WSSA:
“Superweed: Slang used to describe a weed that has evolved characteristics that make it more difficult to manage due to repeated use of the same management tactic. Over-dependence on a single tactic as opposed to using diverse approaches can lead to such adaptations.”
“The most common use of the slang refers to a weed that has become resistant to one or more herbicide mechanisms of action (www.weedscience.org) due to their repeated use in the absence of more diverse control measures.”
OK, I’ll go with this definition.
But the WSSA is careful to point out that so-called “superweeds” can arise not only from the overuse of a herbicide, but also ““Dependence on a single mechanical, biological, or cultural management tactic….“
So, if a single herbicide is used, year-after-year, to kill “weeds”, then this selection pressure promotes the proliferation of individual “weeds” that resist, even tolerate, the herbicide, eventually leading to populations of so-called “superweeds”.
But why are Roundup Ready® crops often blamed for a rise in “superweeds” in recent years?
Cause: Predominance of Roundup Ready® Crops
The estimated annual agricultural use of glyphosate in the USA for 2014 equaled over 250 million pounds, over 10 times more than in 1994.
Why this massive increase?
I think the graph below provides pretty good clues for answering the question. (“HT” = “herbicide-tolerant” & “Bt” = Bacillus thuringiensis. By the way, the “HT” crops are mostly Roundup Ready® crops.)
Effect: Relatively Rapid Appearance Glyphosate-Tolerant “Superweeds”
It seems to me that the evidence that the excess and wide-spread use of Roundup®, due primarily to the huge increase in the adoption of Roundup Ready® crops in the past twenty years (see above graph), have led to the current problems with “superweeds”. But I’m no weed science expert.
What do the experts say?
“…herbicides exert a high selection pressure on weed populations, and density and diversity of weed communities change over time in response to herbicides and other control practices imposed on them. Repeated and intensive use of herbicides with the same mechanisms of action (MOA; the mechanism in the plant that the herbicide detrimentally affects so that the plant succumbs to the herbicide; e.g., inhibition of an enzyme that is vital to plant growth or the inability of a plant to metabolize the herbicide before it has done damage) can rapidly select for shifts to tolerant, difficult-to-control weeds and the evolution of herbicide-resistant weeds, especially in the absence of the concurrent use of herbicides with different mechanisms of action or the use of mechanical or cultural practices or both.” (from Ref. 2 below)
And from the USDA plant physiologist Dr. Stephen O. Duke: “Just as with overuse of certain antibiotics in medicine, overuse of a superior technology has been a recipe for accelerated evolution of resistance. Nature abhors a vacuum, and even though evolution of resistance to glyphosate was thought to be unlikely, or at the most, to occur very slowly and only to low levels, the massive selection pressure caused by the world’s most-used herbicide, has resulted in weeds evolving often novel and unpredicted mechanisms of resistance that can impart resistance to glyphosate doses far above those that are recommended.” (from Ref. 3 below)
OK, now what are farmers to do?
The Road To Nowhere?
In response to increasing number of agronomically-significant glyphosate-tolerant “superweeds”, the chemical companies have developed GMO crops with tolerance to multiple herbicides.
Though this may be a really bad idea, these GMO crops have recently been approved (e.g., see here and here) and are currently being propagated in the fields, already with some unintended consequences.
Will this approach be the ultimate solution to weed control?
Likely not. (Please see here, for example.)
1. What Do We Really Know About Roundup Weed Killer? by Elizabeth Grossman, National Geographic
3. Selection Pressure, Shifting Populations, and Herbicide Resistance and Tolerance by University of California, Riverside
4. Why Roundup Ready Crops Have Lost their Allure, by Jordon Wilkerson, Harvard University
1. Dill, G. M. (2005) “Glyphosate-resistant crops: history, status and future.” Pest Management Science, Vol. 61, pp. 219–224. (Full Text PDF)
2. Vencill, W. K., et al. (2012) “Herbicide Resistance: Toward an Understanding of Resistance Development and the Impact of Herbicide-Resistant Crops.” Weed Science, Vol. 60, pp. 2-30. (Full Text)
3. Duke, S. O. (2015) “Perspectives on transgenic, herbicide-resistant crops in the United States almost 20 years after introduction.” Pest Management Science, Vol. 71, pp. 652–657. Abstract
4. Keim, B. (2015) “Monsanto’s Newest GM Crops May Create More Problems Than They Solve.” Wired, (Full Text)
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