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In our second backgrounder on the Stoa Team Policy resolution, we examine one of the most controversial tools farms use to control those pesky weeds: herbicides.

Ever since the creation of the first modern herbicide, 2.4-Dichlorophenoxyacetic acid (or 2,4-D), scientists have continually aimed to develop herbicides that balance potency, safety, and cost. These herbicides fall into two categories: selective and nonselective herbicides. While selective herbicides are engineered to target specific weeds, while nonselective (sometimes referred to as broad spectrum) herbicides are more potent and often indiscriminately affect plants when applied.

Enter herbicide resistant (or HR) crops. As a paper in Environmental Sciences Europe pointed out, “The emergence of herbicide-resistant genetically engineered crops in 1996 made it possible for farmers to use a broad-spectrum herbicide, glyphosate, in ways that were previously impossible.” This dramatically changed the way farmers protected their crops from weeds, and by 2011, “an estimated 94% of the soybean area planted, 72% of corn, and 96% of cotton were planted to HR varieties”

One of the purported benefits of this new kind of crop has been a reduced amount of herbicide usage overall, due to the fact that the crops themselves are immune to the effects of the herbicide. This has not been the case. In fact, the opposite has proved true, and usage of the most popular herbicide, glyphosate, has risen dramatically. According to The New England Journal of Medicine, “In the United States, glyphosate use has increased by a factor of more than 250 — from 0.4 million kg in 1974 to 113 million kg in 2014.”

In addition, the prevalence of herbicides like glyphosate and 2,4-D are due to a few other factors. These herbicides are flexible and cheap, allowing farmers to grow their profit margins by spending less on weed control and use them in conjunction with other herbicides to avoid weeds developing resistance to a specific herbicide (we’ll get back to this later). They are also valued highly because of how effectively they absorb into the soil, leaving less residual herbicide and reducing their effect on future crops. Lastly, herbicides like glyphosate are used “to provide an alternative tool for the management of weeds that have already evolved resistance to particular herbicides”

As with many cases in which cheap solutions are used in lieu of safer option, the current pattern of herbicide usage has some serious problems.

The first of these is the rise of herbicide-resistant weeds, or “superweeds.” These weeds jumped into the public spotlight in 2014 when Dow Chemical, the company that manufactures HR crops and herbicides, admitted that the magnitude of the superweed infestation had doubled from 2009 and that the damage caused by the plants had amounted to $1 billion. The effects of this were especially dire in agriculturally centered states like Georgia. In 2004, strains of herbicide-resistant crops were found in only one county. By 2011, that number jumped to 76. Jay Holder, a farming consultant in Ashburn, Georgia, articulated the magnitude of this when he told Nature Magazine that  “It got to the point where some farmers were losing half their cotton fields to the weed,” How did this happen? Well, it’s a little complicated.

Essentially, when one herbicide is used consistently and at high volumes, it exerts a high “selection pressure” on the plant life in the area. Without getting into the weeds here, (heh heh heh) a high selection pressure means that plant life there begins to grow resistant to whatever is causing the pressure. As the Food and Agriculture Organization (FAO) put it, “When glyphosate is sprayed 2-3 times annually at high rates it imposes a high selection pressure on the weed flora. In 5-8 years this may cause shifts in weed composition towards species that naturally tolerate glyphosate” Furthermore, the concern was raised as far back as 1992 that this resistance could spread via cross-pollination to other plant life, growing the problem.

This is why most researchers recommend that these herbicides be used as part of a more diverse strategy, to avoid the kind of selection pressure that creates these superweeds. Unfortunately, this hasn’t happened. As that previously mentioned Nature Magazine article explained, “Farmers had historically used multiple herbicides, which slowed the development of resistance. They also controlled weeds through ploughing and tilling — practices that deplete topsoil and release carbon dioxide, but do not encourage resistance.” But it gets worse. The article goes on to explain that farmers have responded to the proliferation of resistance by using more glyphosate. Sounds like it would work out great, right? This increase in application is expected to raise the the total herbicide usage in the US from 1.5 kilograms per hectare in 2013 to 3.5 kilograms per hectare in 2025.

This increased herbicide usage has resulted in a growing concern for public health. While glyphosate is largely considered to be one of the safer herbicides, the volume in question raises serious concerns about how the increase in application changes public health considerations. As usage increases, the possibility of herbicide residue left on food and in the air rises. As Environmental Sciences Europe found “Two-thirds to 100% of air and rainfall samples tested in Mississippi and Iowa in 2007–2008 contained glyphosate.”

Should we be worried about the possibility of herbicide residue? Well, there’s a lot of disagreement about that. In 2000 and 2004, the National Academy of Sciences found the genetic modification of crops needed to make HR crops posed no risk no public health. The risk, in reality, comes not from the genetic modification of the crops, but from the resulting overuse of glyphosate and 2,4-D. In 2015, the International Agency for Research on Cancer (IARC) classified glyphosate as a “probable human carcinogen” and 2,4-D as a “possible human carcinogen”  (in case you didn’t know, a carcinogen is a substance capable of causing cancer.) In addition, studies have found that inert ingredients in Roundup (a very common herbicide produced by Monsanto that contains glyphosate) can cause serious problems for pregnant women. Granted, the tests found that these risks were only significant when Roundup was used in huge amounts, the exponential increase in herbicide usage does make this a serious concern. (Although this, like a lot of things, is certainly up for debate.) Some think this problem will solve itself – as farmers continue to use more herbicide to deal with herbicide resistance, the argument is that eventually it will cease to be cost-effective and they will have to use other measures.


So why should you care about this? For two reasons.

  1. The pattern of herbicide -> herbicide resistant weeds -> more herbicide does pose a real risk to the environment and to public health, and certainly warrants at least a consideration of a change in federal regulation.
  2. Enlist Duo. In 2014 the EPA approved a new herbicide manufactured by Dow Chemicals called Enlist Duo. This herbicide, which is designed to combat herbicide resistance, uses a combination of glyphosate and 2,4-D. After its approval, however, concerns were raised about the studies done on the effects the herbicide might have on the environment and public health, and whether the combination of the two chemicals might pose unique risks not present in either one alone. In addition, some farmers have complained that usage of 2,4-D has a tendency to affect crops outside of where it was meant to be applied, damaging other crops. This caused the EPA to attempt to revoke its approval of the chemical.


Based on the issues surrounding herbicides presented here, a few possible case ideas have come to mind that debaters competing in Stoa might want to consider.

Regulation of specific herbicides.Some herbicides could be considered too harmful to public health and to the environment. Cases regulating their use could have strengths.

Mandate Herbicide rotation. As I discussed, a contributing factor to the growth of superweeds was the lack of diversity in measures used to attack weeds. Overreliance on one herbicide leads to resistance. A case  mandating diversification is one worth looking into.

Delay Enlist Duo (until further studies are done). This one is a bit more squirrely, but there is definitely support for the idea that given the concern of many farmers and the concerning findings of the IARC, further studies need to be done on the chemical before it’s allowed to be used on so much of the nation’s crops.









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