Posted: March 2014
Increasing Weed Resistance to the Herbicide Glyphosate
In the 1970s farmers began spraying the herbicide glyphosate to kill
weeds. Glyphosate, which was developed by Monsanto Company and is sold
under the name Roundup, proved to be an effective broad spectrum
weed killer. Any time such a poison finds widespread use, the likelihood
that the target organisms will develop resistance grows, since organisms
adapt to the changing environment (Délye et al. 2013).
In two decades of moderate use, no weeds were detected that had become
resistant to glyphosate. During this time, Monsanto scientists developed
the first glyphosate-resistant genetically modified (GM) crops—corn,
soybeans, cotton, and canola. These crops do not die when they are sprayed
with Roundup. In a 1997 article—one year after the first commercial
planting of these crops—Monsanto scientists stated that because in 20
years’ use of glyphosate no weed resistance had been found, “it is
reasonable to expect that the probability of glyphosate-resistant weeds
evolving will not increase significantly over that considered with current
use” (Bradshaw et al. 1997). They stated that broader use of glyphosate
with the advent of glyphosate-resistant crops would be a means to “reduce
the potential for further spread of herbicide resistance” (by killing
those weeds that had become resistant to other herbicides).
Nothing could have been further from reality. Weed resistance to
glyphosate has risen dramatically since 2000, when farmers and weed
scientists in the U.S. began noticing that some weeds in fields planted
with glyphosate-resistant crops were becoming resistant to glyphosate—they
didn’t die when sprayed. This problem has increased, and a total of 28
species of weeds show resistance to glyphosate (Heap 2014). The resistant
weeds can be found in 23 different countries (fourteen species are
resistant in the U.S., mainly in fields with GM crops).
The evolution of weed resistance was furthered by the widespread planting
of glyphosate-resistant crops on millions of acres of farmland (mainly the
commodity crops: corn, soybeans, and cotton). While 15 million pounds of
glyphosate were sprayed on corn, cotton and soybeans in 1996, in 2012 159
million pounds were sprayed—a 10-fold increase (Food & Water Watch, 2013;
based on USDA/NASS data).
Before herbicide-resistant crops were available, “weed control required a
higher level of skill and knowledge” (Mortensen et al. 2012). Then farmers
were offered one simple method to control weeds—spraying glyphosate—and
they began planting the same crops year after year on the same fields. The
monocultures of industrial agriculture became more and more pronounced.
Farmers are therefore facing a huge problem and, as an expert on herbicide
resistance recently warned, “U.S. farmers are heading for a crisis” (cited
in Service 2013).
Confronted with weed resistance, farmers first began spraying more
glyphosate and then started to use additional herbicides to try to kill
the resistant weeds. Farmer expenses for herbicides have risen
significantly; for example, farmers who used to pay $25 per hectare for
herbicides are now paying $160 per hectare (cited in Service 2013; see
also Food & Water Watch, 2013).
But this is no long-term solution, since already some glyphosate-resistant
weeds have become resistant to additional herbicides, making them even
more difficult to kill (Heap 2014). The problems will only get worse; they
resemble those the medical profession faces with infectious bacteria that
are resistant to multiple antibiotics.
The biotech industry’s answer to this problem is more of the same. They
have created new GM plants with resistance to multiple herbicides. They
would like to bring more onto the market, and crops resistant to the
herbicides 2,4-D (Dow Chemical Co.) and dicamba (Monsanto) are currently
being reviewed by the USDA in connection with the potential negative
It is hard to imagine how scientists at Monsanto and other biotech
companies can keep a straight face when representing their new
technologies as the solution to problems that their previous technology of
the same kind helped create. Crops with multiple resistances will only
encourage the spraying of more and multiple herbicides and further the
evolution of more weed resistance, not to mention the environmental and
health impacts that accompany increased herbicide use and industrial-scale
monocultures. “This trend would move us in the opposite direction of the
reduced chemical inputs that scientist in sustainable agriculture have
long advocated” (Mortensen et al. 2012).
Bradshaw, L. D. et. al. (1997). “Perspectives on Glyphosate Resistance,”
Weed Technology, vol. 11, pp. 189-98.
Délye, C. et al. (2013). “Deciphering the Evolution of Herbicide
Resistance in Weeds,” Trends in Genetics vol. 29, no. 11, pp. 649-58.
Food & Water Watch (2013). “Superweeds: How Biotech Crops Bolster the
Pesticide Industry,” Food and Water Watch. Available online:
Heap, I. (2014). “The International Survey of Herbicide Resistant
Weeds” (Mar.11). Available online: www.weedscience.org/doc/Superweeds.pdf
Mortensen, D. A. et al. (2012). “Navigating a Critical Juncture for
Sustainable Weed Management,” BioScience vol. 62, pp. 75-84.
Service, R. (2013). “What Happens When Weed Killers Stop Killing?”
vol. 341 (Sept. 20), p. 1329.